Aircraft Starter FAQ & Troubleshooting

For repair information of Hartzell Engine Technologies starters use the OE-A2 (Latest Revision). Make sure you review our new product lines of Aircraft Starters.

I recently installed a new aircraft starter. It engages but cranks very slowly. Sometimes it takes several attempts to start. What could be the problem?
I recently installed an aircraft starter and when I engaged it, I hear only the motor running. What is the cause?
After starting several times with a new starter, I noticed that some damage was evident on the starter ring gear. Please explain?
The starter drive will not engage every time, when it does the start is normal. What is the reason?
I've been told that the starter drive needs to be lubricated. Does the starter drive need to be removed from the starter to do this? How often should I lubricate and what product is best to use?
I have a broken gear on my aircraft starter, what could be the causes?
I have been told I have a bad starter. While it is easy to replace, I would like to know some of the things that are found bad?
I recently installed an E-Drive aircraft starter and it stays engaged for three or four propeller rotations and then disengages. What could be the problem?
You say there is a circuit board inside the starter? What is it's purpose?
On the E-Drive starter I've noticed the starter drive gear does not stay engaged with the flywheel if the engine does not start as in the older Prestolite style starters. Why??
Will the E-Drive and X-Drive aircraft starters fit any Lycoming installation?
Speaking of X-Drive, what makes that starter unique?
I just installed an X-Drive starter, hooked up the starter cable, turned the key and nothing happened. What's the problem?
I am installing an X-Drive aircraft starter and cannot install the one bolt used on most starter installations due to clearance issue between the pinion and the solenoid. What should I do?

Q: I recently installed a new aircraft starter. It engages but cranks very slowly. Sometimes it takes several attempts to start. What could be the problem?
Check the obvious things first. A weak battery will cause this condition. If you engage the aircraft starter and the propeller moves but stalls, feel the starter solenoid and battery cables quickly. If they are cold the battery is most likely bad but if they are hot, suspect corrosion in the in the electrical system and check further.

A poor ground at battery box is a very common condition causing slow starter performance. Any resistance to starter causes heat. If the connection is warm then you need to clean the connection to reduce the electrical resistance. Battery terminals once removed should be made bright and shiny. Even a half ohm resistance in the ground circuit can cause a significant reduction in power to the starter.

While the same conditions above can occur for Continental engines, the most likely cause is slipping starter adapter. This requires replacement or overhaul of the starter adapter.

Another area to inspect would be the ground cable that attaches between the engine and the engine mount and/or airframe. Many of these ground cables are a braided strap that is manufactured to allow movement but unfortunately, is sometimes connected to the engine mount with a clamp. Make sure the clamp is tight to the mount and the area under the camp has been scuffed off to provide a good grounding surface, especially if the mount has been recently painted after an overhaul.

There were some aircraft that were manufactured using aluminum wiring from the battery to the master solenoid. If these cables have not been replaced, they would be very suspect as a source of high resistance.

Q: I recently installed an aircraft starter and when I engaged it, I hear only the motor running. What is the cause?
If the starter end plate containing the brushes was installed 180 degrees out, the starter will run backward thus causing the starter drive (Bendix) to slip. This condition can be incorrectly diagnosed as a defective aircraft starter drive. There are markings on the end plate CW/CCW (L & R on the Prestolite style) pertaining to the direction that the starter should rotate the engine.

This condition could also be the starter drive not engaging because it is stuck or the teeth have been damaged. Drive teeth on the Bendix come based on how many teeth are on the starter ring gear. An incorrect match can wear some teeth down.

If this condition happens on a Continental engine it is most likely the starter clutch slipping.

Q: After starting several times with a new starter, I noticed that some damage was evident on the starter ring gear. Please explain?
Incorrect pitch on starter drive (Bendix) or incorrect pitch on ring gear part of the engine installation. On Lycoming engines there are two different starter ring gears. One has 122 teeth (10/12 pitch) and the other has 149 teeth (12/14 pitch). The shape of the teeth can also identify them. The 122-tooth have squared-off valleys between the teeth and the 149-tooth have rounded valleys between the teeth. Of course to be certain, count the teeth. The starter drive gear (Bendix) must match the starter ring gear or damage will occur by wearing down the teeth on the ring gear. The 122-tooth ring-gears were mostly on early Lycoming powered airplanes. Later aircraft were manufactured with 149-tooth ring gears. However, this only remains true if the engine or the ring gear has never been changed. Sometimes the engine or even the ring gear has been changed to the later 149 tooth version. Diametral pitch pertains to the number of teeth per inch of gear diameter. The first number indicates the number of teeth, and the second number indicates the height of the teeth. The starter drive and the starter ring gear must have gear teeth with the same diametral pitch. Always count the teeth on your engine's ring gear to assure the proper starter/ring gear combination will be installed.

Another factor may be the starter solenoid contact bouncing closed during flight causing starter to engage. Gear damage may also be caused by the new Lightweight type starter being engaged while engine still turning. (Although less common, this can be caused by any type of starter not just the lightweight.)

Q: The starter drive will not engage every time, when it does the start is normal. What is the reason?
There are really two suspects here. If the starter drive (Bendix) sticks intermittently it is probably in need of lubrication. The starter drive is a mechanical device which has only the initial lubrication to allow smooth operation and sometimes a considerable speed. The gear must move in and out and also rotate. If it becomes dry of lubrication it can sometimes stick and fail to engage or disengage. The starter drive must be lubricated when the airplane reaches each fifty (50) hours of operation. If this condition has occurred after the starter has been in service for some time without maintenance or at any time severe environmental conditions, immediately lubricate or replace the starter drive .

The other likely factor for intermittent engagement would be a faulty starter solenoid. If you want to check a solenoid, it is best to do so with a load applied. Resistance in the solenoid, even a fraction of an ohm is enough to produce poor, or no operation due to the high current field. In a 12 volt starting circuit drawing 60 amps, for example, the addition of 0.2 ohms of resistance due to an oxidized connector or carbonized contact may drop the current to the load to 36 amp. This is a 40% loss in starter operating power caused by a 0.2 ohm resistance!

Checking the circuit without a load would require that a lot of resistance be placed in line. The best method of checking the solenoid is to disconnect the lead from the starter and connect it to a battery load-meter tester. Activate the relay and check the voltage on each side of the relay. A 0.1 volt drop is normal for a new or near new relay. If you find any more than 0.3 volt drop, replace the relay.

Q: I've been told that the starter drive needs to be lubricated. Does the starter drive need to be removed from the starter to do this? How often should I lubricate and what product is best to use?
The starter drive (Bendix) is originally lubricated with Lubriplate 777 at Hartzell Engine Technologies. This is recommended, however if the drive is being cleaned and re-treated an aircraft quality silicone spray may be used as well. Oil or common greases should not be used as they will attract and retain dust and grit causing the starter drive to stick or wear rapidly.

Q: I have a broken gear on my aircraft starter, what could be the causes?
In some cases engine kick back will fracture starter drive gears. Kick back is related to engine set up and can be anything from incorrect timing to problems with the fuel system. If kick back is noticed as a common occurrence on the airplane, diagnose and repair the problem or the replaced starter drive may fracture again. The New E-drive Aircraft Starter is completely immune to Kick-backs and has an unlimited 2yr warranty. This may solve your problem.

This condition can also be related to the starter drive extension and retraction. If during the normal extension, the gear is not inserted all the way, stress will be placed on the drive gear. If the starter drive is not removed from the start, the engine will tend to drive the gear placing stress on the gear. In either case, the gear will rapidly wear or fracture. If the starter drive is engaged all the way but does not retract, the ring gear will drive the starter motor and quickly over speed and destroy the motor. If no damage is apparent but the drive has failed to extend or retract, lubricate or replace the starter drive.

Q: I have been told I have a bad starter. While it is easy to replace, I would like to know some of the things that are found bad?
You have bad starter is a catch phrase for many conditions. It can mean just the need to replace brushes. On most of the Delco or Prestolite styles you can remove the cover and inspect the brushes and commutator. The brushes should be making good contact and have plenty of brush spring tension. Inspect the commutator for dirt, burns, or high mica. The mica should be undercut to a depth of 1/32 inch. If you see burned bars on the commutator, you may have an open armature which will prevent proper turn over. If the starter has low speed but high current draw, then you could have an armature dragging, a shorted armature. (Check armature on growler), or a grounded armature or field. If the starter has high current draw and no speed then this most likely is a direct ground or frozen shaft bearings. If there is no current draw from the starter then it is likely you have an open field circuit or open armature coils. If you find the starter has low speed and low current draw then this may indicate an open field winding or a high internal resistance caused by defective leads, dirty commutator, or poor connections. Finally, if the starter runs at high speed with no load but has little torque when load is applies the fault is probably a shorted field. There is no easy way to detect shorted fields since the field resistance is already low.

Q: I recently installed an E-Drive aircraft starter and it stays engaged for three or four propeller rotations and then disengages. What could be the problem?
Early production models of the E-Drive were susceptible to excessive aircraft system voltage drop, resulting in pinion hold in issues. A revised circuit board and solenoid coil have resolved this issue. The following checks can help determine if the starter should be replaced with an upgraded unit. First, verify the voltage at the battery. Next, verify the voltage drop at the starter is not more than ½ volt less than the system voltage. If these two voltages are within acceptable limits, there may be a problem with the circuit board located within the starter. As this is not a field replaceable component, the starter will need to be replaced.

Q: You say there is a circuit board inside the starter? What is it's purpose?
The circuit board inside the starter is installed to control the operation of the internal solenoid. The circuit board senses the aircraft system voltage during the starting cycle and engages/dis-engages the starter accordingly.

Q: On the E-Drive starter I've noticed the starter drive gear does not stay engaged with the flywheel if the engine does not start as in the older Prestolite style starters. Why?
The E-Drive starter is unique in that it uses an internal solenoid to control the engagement/dis-engagement of the drive gear into the ring gear. Gone are the days of a Bendix drive hanging up in a ring gear because it did not disengage when the engine was started. In addition, because the starter drive gear disengages after each starting attempt, the engine is much easier to hand prop should the battery be too low to provide normal starting voltage. Though we do not recommend had-propping an engine, it does occasionally still happen in the field.

Q: Will the E-Drive and X-Drive aircraft starters fit any Lycoming installation?
Excellent question as it is one that anyone in the field has stumbled over at one time or another. All of our starters are manufactured to fit, operate and meet certain engine requirements as specified and manufactured by Lycoming. However, when these engines are purchased by the airframe manufacturer, certain modifications may be made with regards to baffling, oil cooler and fuel line installations and other installed components that may not be part of the original engine design. Consequently, a starter that is a PMA'd replacement for another starter may not always fit the actual installation of the engine in the airframe. That is one of the reasons we offer a variety of models in our "E" and "X" drive series starters.

Q: Speaking of X-Drive, what makes that starter unique?
Our X-Drive aircraft starter is an external solenoid starter that is offered in both left-hand and right-hand models (as viewed from the pilots seat). The external solenoid offers a shorter overall package without sacrificing any starter power as the motor on the "E" and "X" drive are the same.

Q: I just installed an X-Drive starter, hooked up the starter cable, turned the key and nothing happened. What's the problem?
It sounds as though the solenoid is not being energized when the starter system is being engaged. I would recommend checking to verify there is a 16 gage jumper wire between the power terminal where you connected your starter cable and the small spade terminal between the two large terminals. This will supply power to the solenoid which will close the contacts, allow battery power to flow to the motor and mechanically engage the drive gear into the engine ring gear.

Q: I am installing an X-Drive aircraft starter and cannot install the one bolt used on most starter installations due to clearance issue between the pinion and the solenoid. What should I do?
The bolt as specified in the Lycoming parts manual will not fit in the clearance provided between the solenoid and the pinion housing. The best cure for this is to install a fourth stud in that location using the same part number as the other studs already installed.

Fuel Pump FAQ & Troubleshooting

I bought a fuel pump from one of your distributors, installed the fittings and then installed the pump on my engine. I find it works fine at higher RPM's but won't support the engine at idle speeds without the boost pump on. What's going on?

Q: I bought a fuel pump from one of your distributors, installed the fittings and then installed the pump on my engine. I find it works fine at higher RPM's but won't support the engine at idle speeds without the boost pump on. What's going on?
Our biggest problem with low pressure at idle speeds is pump contamination. Debris lodged between the valve and seat of the relief valve assembly is the single-most cause of pump failure. The smallest speck of contamination can effectively reduce fuel output pressures or cause the pump to operate in an erratic fashion at lower RPMs. Sediment in the form of rust, scale, lint, sealant, aluminum compounds, have all been known to cause pumps to lose their pressure. It is strongly recommended that fuel lines be flushed prior to installing them to the pump. Furthermore, installation of pump fittings can introduce unwanted Teflon® paste, tape, or material pulled from the fitting or housing itself. Be certain to clean the fittings and pump threads thoroughly before installing the fittings to the pump. Avoid using a vise to hold the pump when installing or repositioning fittings, as this can permanently damage the assembly. If possible, mount the pump to the engine prior to making any fitting changes.

On occasion, fuel-borne contaminants can actually be purged from the relief valve seat. The procedure is simple. First, remove the safety wire that secures the 9/16-in. jamb-nut to the valve housing and turn it one-half turn to loosen it. Next, using a straight-bladed screwdriver, turn the relief valve adjusting screw counter-clockwise until it no longer turns. The screw has an internal stop that prevents it from falling out. It's important that you count the amount of turns required to fully release tension on the relief valve spring. Now, with the throttle in the wide-open position and the mixture at full rich, engage the boost pump for a few moments. Before attempting to restart the engine, be certain to return the adjustment screw to its original setting and safety-wire the nut. About 30 percent of the time this effectively flushes the contaminant from the seat. The odds aren't great, but it's worth trying before removing the pump and sending it out to a reputable Repair Station to be repaired.

Proper fitting installation procedures, including proper use of thread sealants is critical to proper pump operation. In addition, many operators who receive pumps with fittings installed move those fittings to accommodate their installations. In some cases, the loosening and re-tightening of those fittings creates a sliver of metal cut from the cast pump housing threads by the steel fitting or pipe sealant or delaminated plating from the fittings to migrate to the relief valve seat within the pump. Extreme caution and care must be taken when installing fittings and fuel pumps on engines in the field.

Magneto FAQ & Troubleshooting

Remember, any actual repair activity must be done in accordance with the appropriate maintenance or service manual from the applicable source. (manufacturer/airframe and/or engine to latest revision). Read more about our Aircraft Magnetos.

I recently installed an overhauled magneto. The engine seems to start better if the battery is low. What could be the problem?
I am having trouble starting and I don't seem to hear the impulse coupling "click" from the magneto. Any ideas?
I have hard starting sometimes but not always. Am I looking at a potential magneto problem?
During a cold start I seem to have trouble starting and sometimes I get a backfire or two. Should I suspect the magneto or timing?
I have some time on my airplane engine and it is hard starting all the time. Some suggestions please?
I have a shower of sparks magneto and after some difficulty in starting, it now just won't start. What's up?
I have a shower of sparks magneto and it appears to be totally dead. What's the best place to start?
I just returned my airplane from maintenance and I am experiencing "kick back" during start which has not happened before. Some suggestions please?
I have discovered I have a dead left magneto. What should I look for as the cause?
My airplane has been rough running more as the altitude is increased. Any thoughts on this?
On the initial flight of the day, the engine runs smoothly until twenty or thirty minutes into flight. The engine starts to get rough. If I fly again the next day, the engine operates fine for the first twenty or thirty minutes and gets rough again. Any thoughts on this?

Q: I recently installed an overhauled magneto. The engine seems to start better if the battery is low. What could be the problem?
In most cases this is related to the impulse coupling. The engine is firing too early in the stroke. Magnetos are timed to the engine to provide the spark at 20 to 25 degrees before top dead center of the piston compression stroke. This timing is designed to provide the best engine efficiency at normal operating speeds. Since starting occurs at a low engine RPM, the magneto timing must occur closer to top dead center to fire the piston. The job of the impulse coupling is to delay magneto firing from 20 degrees before top-dead-center to near 5 degrees BTDC by building in a 15 degree lag into the impulse coupling. The degree of impulse coupling retard is directly related to crank speed. The retard angle is determined by the impulse coupling not cranking speed. If the cranking speed is too high it will disconnect the impulse coupling. This same condition may also appear as a start-up when the starter switch is released. When troubleshooting, keep in mind that the impulse coupling may not be at fault but the combination of starter and magneto. A typical hard starting problem may occur if you change to a lightweight starter that cranks faster. You must look into whether the impulse coupling is correct for the new starter.

Q: I am having trouble starting and I don't seem to hear the impulse coupling "click" from the magneto. Any ideas?
First, be sure that your magneto has an impulse coupling. Many engines have the Shower of Spark's system. This is noted by a buzzing sound in the cockpit whenever the starter switch is engaged. Be certain the magneto off and turn the prop through to listen for a click. The absence of the click (or snap) in an impulse coupling requires action as the coupling is probably bad. To check impulse coupling in the field you will need to remove magneto with impulse coupling (usually left magneto). Rotate the aircraft magneto in proper direction by hand and observe that the flyweights in the impulse coupling contact the stop pins. If they do not, then flyweight axles are excessively worn and impulse coupling must be replaced. If flyweights are in good condition, rotate magneto several times to snap the impulse coupling and determine that the impulse spring is not weak or broken.

Q: I have hard starting sometimes but not always. Am I looking at a potential magneto problem?
Not necessarily, in most cases this is a starting technique. Analyze your conditions. The presence of a strong fuel smell after an aborted start may indicate a flooded engine. For most airplanes, crank engine with throttle full open and mixture in idle cutoff. (Always refer to the Flight manual or POH for specific procedure.) Also, letting the engine sit for a short period also helps get rid of excessive fuel.

Follow the airplane procedure for throttle valve setting. Generally a nearly closed throttle for cold starts and a somewhat open throttle for warm engine starts. A closed throttle allows the idle fuel tubes to flow fuel and limits the air. This is a rich mixture, which is easier for the ignition system to fire. Opening the throttle reduces the amount of fuel and increases the air to the engine creating a lean start mixture. If you have a warm engine you may wish to open the throttle slightly to allow a little less fuel and a little more air to enter the engine.

Q: During a cold start I seem to have trouble starting and sometimes I get a backfire or two. Should I suspect the magneto or timing?
The most likely cause is either too much prime or not enough. Make sure primer is not leaking. A leaking primer will sometimes cause backfiring or popping due to ignition in the induction. Check to be sure that the primer nozzles are not clogged. Many primer nozzles are close to the intake valve and will clog with carbon. Since some cylinders are hotter than others, all of them will not carbon up equally, so one cylinder may get all the primer fuel. Make sure that the primer nozzle has the proper diameter orifice. If the hole is too large too much fuel is pumped into the cylinder. This can cause difficult starting in cold weather. Some engines like the Continental TSIO-360 take a what seems to be an excessive amount of prime to start, thus giving them a bad reputation for starting in cold weather.

Q: I have some time on my airplane engine and it is hard starting all the time. Some suggestions please?
Start with the magneto internal timing adjustment. If proper adjustment of the "E" gap seems to be drifting, it is most likely because of point or follower wear. This is a common problem with magnetos that have not had routine maintenance. Check for cam wear.

The cam follower is the cam on the rotating shaft that bumps open the points twice per revolution. As this wears, the points open later and do not open as much. This changes magneto to engine timing and makes a weak spark. It is especially critical that dual magnetos be checked. The cam will have two points wearing on the cam. In most cases the wear will be the same since maintenance or original installation occurs at the same time. The cam follower wear will weaken both magnetos and could cause both to falter at the same time or near the same time.

Bendix magnetos use a porous iron cam. By design, the porous iron will tend to absorb lubricant. When inspecting the cam, look for a shinny surface. This is a sign that the cam is worn out and can not longer absorb oil.

Other faults for hard starting could be an incorrect magneto installed on the engine causing incorrect impulse coupling lag angle. A bad magneto capacitor which may develop internal faults or faulty connections. If the magneto has been overhauled or parts replaced, check for incorrect distributor cam on the magneto rotor checking "E" gap timing.

Q: I have a shower of sparks magneto and after some difficulty in starting, it now just won't start. What's up?
Check the voltage before replacing parts. If you have low voltage at vibrator input you might not get a start. Measure voltage between vibrator terminal marked "in" and ground terminal while operating starter. It must be at least 8 volts on 12 volt system, or 13 volts on 24 volt system. If voltage is acceptable, listen for periodic buzzing of the vibrator during start cycle. If no buzzing is heard, either vibrator is defective or the circuit from the output terminal on the vibrator to the retard contact is open. Check both switch and retard circuit for continuity and good electrical ground. You should hear the vibrator tone change as the magneto breakers open and close. If the tone doesn't change, check out the wiring to the magneto. Also check the contact springs in the magneto breaker cover to assure solid contact.

Q: I have a shower of sparks magneto and it appears to be totally dead. What's the best place to start?
Start by checking the magnetos retard contact assembly to see if it is operating or has fouled contacts. If the retard breaker points do not close, you may be starting with a full advanced spark that may cause a kickback. A broken wire to the retard breaker or a poor connection at the magneto may be the cause. You could also be looking at improper adjustment or a bad electrical connection in the circuit.

Another likely cause would be that the magneto and/or vibrator is weak or failed. A quick way to check for this is to disconnect starter and all spark plug leads. (Observe all maintenance manual precautions before trying this.) Rotate the prop in the normal running direction until retard point opens at the number one cylinder firing position. Using one gloved hand, hold the number one plug lead slightly over one quarter inch from ground. Energize the vibrator by turning the switch to start. Plug lead should throw a shower of sparks to ground. Check to be sure the internal timing in the magneto is correct. The shower of sparks will continue over several degrees. The duration may be checked by holding switch in "start" position, and hand turning prop until sparks stop.

Q: I just returned my airplane from maintenance and I am experiencing "kick back" during start which has not happened before. Some suggestions please?
Several things may be the cause here. If the other items in the FAQ have been checked try this one. The starter switch may be wired backwards with the Start occurring on right magneto instead of left. The left magneto is usually the impulse magneto, so if the starter switch is wired in such a way that the magneto without an impulse coupling is grounded during start. Engine will kick-backwards due to the early firing of the non-impulse magneto. The engine will kick backwards due to the early firing of the non-impulse magneto. On aircraft engines with Bendix type starter drives, this condition has the potential to break the drive gear or even the starter housing.

Q: I have discovered I have a dead left magneto. What should I look for as the cause?
Dead or rough running aircraft magnetos. If anything interferes with voltage production in the magneto's primary circuit it will prevent it from firing. Some common faults are a bad condenser, bad ignition filter, improper "E" gap setting, and "P" lead problems. A common problem is the "P" lead wire. If this wire is chafed so that it intermittently grounds, it intermittently turns the magneto off. Also check to make sure the "P" lead is attached to the correct starter switch position, i.e. left mag to left mag position. To field check the magneto condenser or ignition filter, consult the magneto or airplane maintenance manual. On Lycoming 540 series engines, if unable to time left magneto on engine, inspect magneto adapter bearing for failure.

Q: My airplane has been rough running more as the altitude is increased. Any thoughts on this?
The first thing to look for is carbon arc tracking inside magneto. The spark developed in the magneto will take the path of least resistance to ground. The spark should occur across the spark plug gap but if the resistance there is higher than at some other point in the high voltage path, the spark may occur somewhere else resulting in a rough running engine. This could due to worn out spark plugs, a dirty or improperly timed magneto. The high voltage charge jumped to ground inside the magneto rather than at the spark plug gap. A magneto may have a good mag check but when full power is low takeoff power was experienced due to the internal mag arcing. As engine power goes up the voltage required to jump the gap at the spark plug increases.

On the outside of an internally arcing magneto, you will most likely see white deposits and removed paint on the upper end. This will be a good indication that something bad is happening inside the magneto. Check the spark plug terminals. They should be clean and the terminal screw clean. If it appears burnt then suspect that the harness contact spring is bad and needs replacement or that the resistance inside the spark plug is bad and the plug requires replacement. Make sure you clean and inspect the terminal end as well as you do the electrode end of the spark plug. Do not use contact cleaners as they may leave deposits that may break down into corrosive compounds. Clean with MEK (Methl Ethyl Ketone) Acetone or Alcohol.

Q: On the initial flight of the day, the engine runs smoothly until twenty or thirty minutes into flight. The engine starts to get rough. If I fly again the next day, the engine operates fine for the first twenty or thirty minutes and gets rough again. Any thoughts on this?
The most likely cause for this would be a faulty magneto coil. When magneto coils start to fail, they usually break down when hot. The engine runs smoothly until around thirty minutes into a flight before it gets rough. The next day, when the coil has cooled down, the engine will operate normally when first started. The magneto also will test OK on a bench test most of the time. If you suspect this problem, heat the magneto in an oven to 140 degrees F for an hour and then run a bench test. Most magnetos will perform the best when the air temperature in the engine compartment around the magnetos are around 125 degrees F. Magnetos should not be exposed continuously to temperatures above 160 degrees F. Airplanes which have higher engine compartment temperatures will install air blast tubes to keep the temperature down, make sure that they are properly installed and clear of obstructions. It should be noted that capacitors are also heat sensitive.

OEM Aircraft Alternator FAQ & Troubleshooting

For repair information of Hartzell Engine Technologies alternators use the OE-A2 (Latest Revision). Also make sure you review our Factory New Aircraft Alternator product lines.

I purchased a replacement engine from the factory, it has a Hartzell Engine Technologies alternator installed. If I have a problem with it, do I return the unit to Hartzell Engine Technologies directly?
I removed my aircraft alternator after many hours of operation, installed your overhauled unit, tensioned the belt properly but after starting the engine the alternator will not work?
During flight, my alternator dropped off line and would not reset. I installed one of your overhauled units. On ground run-up the alternator worked fine but once in flight the alternator dropped off line and would not reset?
I have installed a new unit to replace a worn out alternator, during flight the alternator will drop off line but cycling the switch will reset it every time. What can be done to eliminate this?
After installing an overhauled gear driven aircraft alternator, I am experiencing a loss of power (observed on my ammeter). What are the possible causes?
After installing a new belt driven alternator, I am experiencing a loss of power (observed on my ammeter). What are the possible causes?
During flight, I am experiencing an increasing amount of radio noise. The alternator has been installed for years. Any suggestions?
Upon changing an alternator, it was determined that it had an open (burnt) stator. What could cause this? Before installing another alternator what should I check in the airplane to avoid another possible problem?
Shortly after changing an alternator, the rotor shorted out (burnt up). What could cause this? Before installing another alternator what should I check in the airplane to avoid another possible problem?
I suspect the rectifiers (diodes) are going bad in my alternator, what is the best way to check for this condition before removing from the airplane?
With considerable time on my alternator, I am considering having my mechanic change the brushes. How do I know if this is necessary and is it an easy process?
After installing your overhauled aircraft alternator, the belt keeps coming off the pulley. What is wrong?
My ammeter shows a steady oscillation back and forth. How can I cure this?
I recently replaced the alternator on an old airplane that had been out of service for awhile. The new alternator has higher voltage but lower than specified current output. Before I reject the alternator, what other things can I check out?
How do I check for a bad rotor?
How do I check for a bad stator?
I am performing an annual (100 hr) inspection. Is there any preventative measures or things I can check to assure long life of the alternator?
I recently installed an overhauled alternator on my twin engine airplane. I have not been able to parallel the two alternators. What is the most likely cause?
I paralleled the alternators on the ground successfully but the pilot reported after the first flight that the electrical load balance shifted to imbalance after a short period? Why might this occur?

Q: I purchased a replacement engine from the factory, it has a Hartzell Engine Technologies alternator installed. If I have a problem with it, do I return the unit to Hartzell Engine Technologies directly?
No, the "engine factory" purchased the units from us so they are responsible for this activity. File a claim with the company you purchased the engine from. There are several reasons for this. Many times the engine manufacturer will offer warranties longer than we do. Also since you did not purchase it separately, you will not know the exact installation date which will determine the term of our warranty. This answer also applies to new aircraft, file a claim through them directly, in most cases they have a significantly longer warranty period as well.

Q: I removed my aircraft alternator after many hours of operation, installed your overhauled unit, tensioned the belt properly but after starting the engine the alternator will not work?
Make sure the aircraft wiring is correct. Most of the Prestolite style alternators have two field terminals. One of these has to be grounded either through the regulator or directly to airframe. The next thing to check is to make sure you have power to the field. With the engine not running and the system turned on you should have about battery voltage at the field. If you have voltage at the field and the field is properly wired the alternator should work.

Q: During flight, my alternator dropped off line and would not reset. I installed one of your overhauled units. On ground run-up the alternator worked fine but once in flight the alternator dropped off line and would not reset?
High resistance in the field circuit causing the over-voltage relay to trip can develop. Check terminal connections and make sure the field wire was not secured too tightly as stress on the wiring can result in intermittent contact. Do not rule out a defective voltage regulator.

Q: I have installed a new unit to replace a worn out alternator, during flight the alternator will drop off line but cycling the switch will reset it every time. What can be done to eliminate this?
Check the voltage drop in the field circuit. If the voltage differential between the airframe buss and the field terminal is more than 1/2 volt you probably have a bad field circuit breaker, bad alternator switch, bad wiring connections or a combination of the three. Note: The average airplane age is in excess of twenty years and few have had the circuit breakers replaced, corrosion, using the breaker as a switch, and moist conditions tend to allow the contact points of the breaker to acquire resistance, which in turn will change the voltage and current values in the airplane's electrical system.

Q: After installing an overhauled gear driven aircraft alternator, I am experiencing a loss of power (observed on my ammeter). What are the possible causes?
Although there are many possibilities, most likely this is caused by the coupling gear slipping. TCM (Continental) has several service bulletins addressing the slippage torque on coupling gears. (M89-5 and SB95-3A are two)

Q: After installing a new belt driven alternator, I am experiencing a loss of power (observed on my ammeter). What are the possible causes?
The primary thing to look at is the belt tension, especially if you are noticing loss of power in precipitation. Consult the aircraft or engine service maintenance manuals for precise instructions. If the tension is proper, make sure the aircraft wiring is correct. Check that the field terminals are not loose at the ground through the regulator or at airframe. The next thing to check is to make sure you have power to the field. With the engine not running and the system turned on you should have about battery voltage at the field. If you have voltage at the field and the voltage regulator is suspect.

Q: During flight, I am experiencing an increasing amount of radio noise. The alternator has been installed for years. Any suggestions?
This can be a simple condition or very difficult. All alternators will make a little electrical noise as this in inherent in their design. If the problem just suddenly appeared (no new radio or antenna installs) you could be looking at a break down of the alternator rectifiers (diodes). This will appear as AC voltage on the airframe's DC buss. You can check this by oscilloscope or a simple voltmeter. In either case, probe the output terminal on the alternator while running and look for less than one volt of AC. (If using a voltmeter, be sure you select the AC scale.) If you see more than one volt, this is most likely what you are hearing over the radio and the alternator should be repaired for bad or leaky diodes or replaced. If you do not see AC above one volt then let the alternator warm up for a short period and probe again. If you do not see it then, the alternator is not at fault.

The next most likely cause is the battery terminals, check and make sure they have clean and bright surfaces. Inspect the cable attached to the terminals looking for corrosion creeping under the insulation. With cables removed from the battery, check to assure that no more that .2 ohm exists to ground. If you have an older airplane, check that the power and ground cables to the battery and alternator are not aluminum. (There are Service Bulletins and instructions from many manufacturers regarding the replacement of these cables.) Aluminum battery cables are very hard to inspect in some airplanes, the corrosion can form inside the cable with no noticeable defects on the outside. Radio noise, hard starting and dimming lights are among the troubles these cables present. It is recommended that they be changed. Of course along with the corroded battery cable comes corrosion in alternator circuit breakers and switches.

Beyond this, radio noise can become complicated. Note the sound of the "noise" before blaming the alternator. A whirring sound, which can be varied at lower rpm, will generally be alternator related but can also be related to other continuously running electrical motors as affected by the buss voltage going up and down. If the noise is steadier and appears to increase with airspeed, the most likely culprit would be static electricity.

Many aircraft manufacturers and avionics installers will install radio noise filter as a "cure all". These are essentially capacitor networks and should they not be installed properly or fail, they can create troubleshooting problems. Look for wire routing changes in any area especially if an antenna has been moved or with new avionics installs, around power buss connections and at grounds. Most all shielded wire must be grounded at either end or they will not be effective for outside noise rejection.

Q: Upon changing an alternator, it was determined that it had an open (burnt) stator. What could cause this? Before installing another alternator what should I check in the airplane to avoid another possible problem?
Generally, burned stators are caused by the wires in the stator shorting to each other. This can be caused by excessive vibration either from imbalances within the alternator or externally. Over temperature can also create this condition. Other than heat and vibration, it is unlikely another fault can cause this condition. For vibration check to see if the belt tension is correct and the pulley is straight. Observe the belt while running there should not be a lot of movement of a properly tensioned belt. For heat, check that the alternator fan is installed and rotating. If there is a blast cooling set up, check that there are no obstructions or kinks in the inlet or hose.

Q: Shortly after changing an alternator, the rotor shorted out (burnt up). What could cause this? Before installing another alternator what should I check in the airplane to avoid another possible problem?
In most cases, the rotor will short-based on manufacturing or assembly reasons. However, over heat will cause the same condition. For heat, check that the alternator fan is installed and rotating. If there is a blast cooling set up, check that there are no obstructions or kinks in the inlet or hose.

Q: I suspect the rectifiers (diodes) are going bad in my alternator, what is the best way to check for this condition before removing from the airplane?
If you have access to an alternator test set, select "ripple voltage" and check. More commonly, you can check this by oscilloscope or a simple voltmeter. In either case, probe the output terminal on the alternator while running and look for less than one volt of AC. (If using a voltmeter, be sure you select the AC scale.) If you see more than one volt, this is most likely what you are hearing over the radio and the alternator should be repaired for bad or leaky diodes or replaced.

Q: With considerable time on my alternator, I am considering having my mechanic change the brushes. How do I know if this is necessary and is it an easy process?
The brushes should be checked every 500 hours regardless of condition. If they do not meet the minimum length specified in their respective manual they should be changed. Time between brush changes can be affected by many things. Dusty or gritty environment outside coming through the fan or blast tube, consistently high loading, excessive vibration, poor grounding, or variables in brush composition are a few common factors. The typical precursor to brush replacement comes in the form of increasing radio noise or occasional tripping of the alternator off line with light loads. Either of these conditions should alert to a brush wear check.

Most of the popular alternator types, Prestolite or Chrysler have brush blocks that can be changed with very little effort. Ford type, however must be disassembled and are much more difficult to replace.

Q: After installing your overhauled aircraft alternator, the belt keeps coming off the pulley. What is wrong?
If it is a Lycoming installation it probably is belt alignment. If it is a Continental installation on the back of the engine it could be belt alignment or de-tuned counterweights on the crankshaft (Lycoming to a lesser extent). If the alternator installed came with a pulley assembly, check to assure that it is the correct one as belts have certain angle and depth requirements. Observe the belt while running, there should not be a lot of movement of a properly tensioned belt.

Q: My ammeter shows a steady oscillation back and forth. How can I cure this?
This condition in normally related to older airplanes. If you airplane has an original style voltage regulator which is low frequency. These older style regulator operate at a frequency at or near the alternator frequency because of this, the alternator and regulator will tend to "follow" one another causing the meter to oscillate. Most all new designed voltage regulators operate and a much higher frequency eliminating the oscillating needle. Along with this, high frequency regulators often offer ground fault protection that will keep a short on the field circuit from damaging the regulator. Many of the most popular airplanes have kits that will allow you to upgrade your airplane. Consult the airframe manufacturer for applicability.

Q: I recently replaced the alternator on an old airplane that had been out of service for awhile. The new alternator has higher voltage but lower than specified current output. Before I reject the alternator, what other things can I check out?
Corrosion, corrosion, corrosion, in most cases this is the problem. Check the common places like battery cables, terminals, ground terminals, connectors, circuit breakers and switches. Some airplanes have the battery located in the tail or far away from the alternator. These should be checked carefully for grounding. If the battery is grounded at the battery in the tail, corrosion in the airframe joints can add up to resistance since most likely the alternator ground is in the engine compartment. There should not me more than 0.2 ohms on ground.

Q: How do I check for a bad rotor?
Using an ohmmeter will give you a good idea whether the rotor is open or not. If you have the rotor out of the unit you can check the resistance per the aircraft alternator manual.

Q: How do I check for a bad stator?
It takes an analog ohmmeter to test the stator for condition. Put the + (plus) lead on ground and the - (minus) lead on the output terminal. The reading should be between 30 & 60 ohms. This test cannot be done with a digital meter! Use the ohms reading for reference only, any repair must be according to the alternator overhaul and repair manual.

Q: I am performing an annual (100 hr) inspection. Is there any preventative measures or things I can check to assure long life of the alternator?
There are many simple checks to help assure the life of an alternator. Start with the connections, make sure each connection is corrosion free, tight and the insulators (as installed) are not cracked and in good shape. Observe the outside of the alternator, shaft and pulley, there should not be a lot of corrosion and rust apparent. If black carbon dust accumulates between inspections more than a simple dusting, the brushes should be removed and checked for wear. Most alternators utilize through bolts to hold the unit together. These through bolts should be checked for torque at each 100 hours of operation or sooner if any distress at the bolt are noted. Replace the alternator belt regularly and check alignment. Old and worn belts can cause undue vibration and may separate or come off in flight.

Q: I recently installed an overhauled alternator on my twin engine airplane. I have not been able to parallel the two alternators. What is the most likely cause?
In most cases, a mismatch between alternators has occurred. All alternators have output tolerances. Generally 10% to 15% of the total output would be a normal tolerance. For twins typically 10 amps split is common. When installing an alternator on a twin, your best bet is to install a new rather than an overhauled unit. New spec's are much tighter than overhauled or repaired units. The fact that an overhauled unit may have been used several times prior to the current overhaul will dictate that service tolerances exist for that purpose. Things like air gap or rotor efficiency will always make for the possibility of a greater variance than on new units. In the perfect situation two new alternators will be installed but realistically, using one existing and one new will give the best results. Of course other things may plague the effort to parallel units.

Q: I paralleled the alternators on the ground successfully but the pilot reported after the first flight that the electrical load balance shifted to imbalance after a short period? Why might this occur?
The most likely reason in this case would be temperature. Most paralleling activity occurs quickly and with a cold airplane. Once the airplane is in operation and the systems are warm, both the alternators and regulators will change slightly. Many times the tight tolerance will be exceeded and one alternator will "take over". When paralleling, the airplane should be brought up to operating oil temps prior to adjustment. While running, place a moderate to high load on the system for several minutes to heat up the system. Then follow the airplane manufacturer procedure for paralleling.

Turbocharging System FAQ & Troubleshooting

Turbochargers, turbo valves and controls are not typically field repairable. Please review our Hartzell Aircraft Turbos for more information.

I notice some small nicks in the compressor blades when inspecting my turbocharger. Can these be dressed out and is there a tolerance?
My airplane acts like I have no turbocharger. I loose power as I go up, but take off power seems normal. What might be happening?
The turbocharger controller seems to be very slow in operation. Any ideas why?
I have noticed some white smoke coming from the exhaust of my turbocharged airplane. I have been told it is probably the turbo. Can there be other causes rather than a bad turbo?
My airplane has a turbo with a wastegate and controller. I am loosing power before critical altitude. What is the most likely cause?
I have noticed high manifold pressure and the engine is easy to overboost. What are the possible reasons?
Sometimes when I pass through precipitation or visible moisture and again occasionally when I adjust for cruise flight I experience a loss in MAP. Any ideas why?

Q: I notice some small nicks in the compressor blades when inspecting my turbocharger. Can these be dressed out and is there a tolerance?
No, due to the very high speed of the turbine/compressor wheel, balance is very critical. Even the smallest bits of damage to the blades can set up an imbalance causing a vibration which will at best reduce the life of the turbo and at worse, cause turbo operation to cease.

Q: My airplane acts like I have no turbocharger. I loose power as I go up, but take off power seems normal. What might be happening?
The most likely cause is the oil supply to the wastegate. Look first to determine engine oil pressure, assure the pressure reading is accurate and is well in the green. This can be in the form of blocked oil lines, or restrictions in the wastegate capillaries. Check oil lines for kinks or blockage. If the condition persists and the oil has been (or previously been) contaminated by any event, the wastegate is suspect and should be replaced or overhauled.

Q: The turbocharger controller seems to be very slow in operation. Any ideas why?
On Lycoming or Continental powered airplanes there are several things to check before changing a controller. First, be sure the oil temperature is in the green (warm), cold oil temps will cause sluggish operation. Check for leaks in the air pressure sensing lines. Look for oil leakage at the compressor outlet air sensing line to the controller. A loose line, corrupted seal or cracked fitting may be to blame. If the oil is dirty or has had some event contaminate the oil, particles may cause the poppet valve (internal) to stick open. Perhaps the most common fault is proper adjustment. Carefully review the airplane maintenance manual and check all adjustment.

Q: I have noticed some white smoke coming from the exhaust of my turbocharged airplane. I have been told it is probably the turbo. Can there be other causes rather than a bad turbo?
There can be many reasons related to the core engine as well as the turbocharger. Many times a turbo will smoke when new due to excessive preservative. However, if the smoke is light and continual, the best suspect is a weak or failed scavenge pump. This would flood the turbo with oil as the scavenge pump is what assists in removing the oil in turbo operation. It should be noted that this same condition can be caused by a blocked or kinked scavenge oil line as well. Continental engines use a check valve in turbocharger oil drain line, should it fail the turbo will flood with oil. (Refer to Continental service information to inspect the check valve.) The scavenge pump condition is best observed by noticing a drop or two of oil out the exhaust pipe after shut down and heavier white to blue smoke each start up.

If the turbo is truly on it's way to failure, several conditions can be noted as precursor. Oil spots or puddles from the exhaust pipe on the ground increasing in size after each flight or run. Heavier white or blue smoke with a failure to maintain low idle condition. (Turbo blades stop turning due to friction.) Continual light smoke due FOD damage to compressor or turbine wheel blades or other internal damage due to contaminated oil. Any of these conditions should mandate immediate attention with the turbocharger replaced or sent for overhaul.

Q: My airplane has a turbo with a wastegate and controller. I am loosing power before critical altitude. What is the most likely cause?
Unless extreme loss of power is experienced, slight reductions of horsepower are hardly noticeable on single engine airplane. On twin engine airplanes, single engine climb, even slight loss of power can be noticed. The first thing to look for is the adjustment on the wastegate. Many wastgates come pre-adjusted to a nominal setting. Depending on the aircraft, the adjustment can be as simple as one setscrew or very complex linkage. Not reaching critical altitude will often show up after a wastegate or other turbo component is replaced.

Many times "power loss" translates into an indication loss, especially if the loss can not felt. Basic airframe instrumentation such as MAP, oil press, TIT and others should be checked for proper reading. If a true loss is suspected, the lines carrying air or oil to the controller or wastegate should be examined for leaks. Loss of manifold pressure in climb on turbocharged engines can also be caused by the butterfly valve in the wastegate is not closing completely. This can be a carbon build up or a wear related condition. Also remember that leaks in the intake and exhaust system may dramatically affect turbocharger operation.

For more extreme or unusual reductions in power as seen in MAP other things should be looked at. Check the compressor impeller for damage. In some cases FOD, including large ice particles will not only nick or dent the impeller but alter the blade contour reducing efficiency or interfering with the housing. Although more difficult to inspect, the turbine (exhaust side) can also suffer from FOD. Should anything pass through the combustion chamber and exit through the exhaust they have the potential for damage. Engine manufacturers have service information regarding the inspection and detection of this subject.

Q: I have noticed high manifold pressure and the engine is easy to overboost. What are the possible reasons?
Although each turbocharged airplane is a little different, the likely causes revolve around the pressure relief valve or the exhaust bypass valve. The relief valve aneroid bellows may be faulty or out of calibration. The exhaust bypass valve is faulty either due to blockage of oil pressure or a mechanical failure. A poppet type (ball) exhaust bypass valve will sometimes stick on its seat leaving it in the closed position. A malfunctioning rate controller can cause the same conditions if it fails to properly sense a rapid increase in compressor discharge thus leaving the valve closed.

Q: Sometimes when I pass through precipitation or visible moisture and again occasionally when I adjust for cruise flight I experience a loss in MAP. Any ideas why?
Both conditions may relate to the same cause. Many turbocharged airplanes utilize alternate air doors that can "suck open" should restrictions block the normal inlet. Many of these suck open doors are held shut with magnets and the pilot lever simply overcomes by pushing in on the door. In the case of precipitation or visible moisture it most likely that some ice is forming and the door is opening. When open the intake air to the turbo comes from within the cowling where the flow is hotter that outside and has no ram effect so the MAP will change. If the magnet has become weak or the opening lever is not adjust properly, even the slightest inlet blockage will open the door. This can also apply to the cruise set up. If the magnet has become weak or the opening lever is not adjust properly, airflow in the cowl or changes in MAP may be enough to open the door. Of course many airplanes have conventional alternate air doors controlled by linkage. Wear or improper adjustment can allow the door to creep open.

Keep in mind that engine air filters can be the problem for either of the above conditions as well. Paper and pleated air filter may collapse with airspeed or may swell with moisture. Of course is always a concern. Pleated air filters that may otherwise look clean may appear "fuzzy" after a few times being cleaned or blown out. This fuzzy texture provides ample area for very small water droplets to form causing a quick icing condition and filter blockage. If the inlet system is tight and there is a mechanical alternate air door, the inlet hoses or tubes can collapse especially if they have not been changed recently. (As pressure drops, the hose or tube contracts and expands aging them.)

Frequently Asked Questions (FAQ)

Aircraft Starter FAQ & Troubleshooting

Fuel Pump FAQ & Troubleshooting

Magneto FAQ & Troubleshooting

OEM Aircraft Alternator FAQ & Troubleshooting

Turbocharging System FAQ & Troubleshooting

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