|
Aircraft parts |
|
Home | Software | Knowledge Base | Customer service | Products |
|
Home> Continental & Lycoming TroubleShoot
Hard Starting. Difficult starting. Won't start. Slow starter. Lycoming or Continental aircraft engine
Slow / Fast cranking speed. The magneto impulse coupling lag angle varies with cranking speed of the engine. If the starter cranks the engine too slow or too fast, magneto firing could occur too far from Top Dead Center for effective starting. Installing a faster cranking starter may require changing the impulse coupling lag angle If the engine has a tendency to start when you let go of the starter switch or if the engine starts better with a low battery; then the engine is firing too early in the stroke. Magnetos are timed to the engine so as to provide the spark at 20 to 25 degrees before top dead center of piston compression stroke. This timing is designed to provide engine efficiency at normal operating speeds. Since starting occurs at very low engine turning speeds, magneto timing must occur closer to top dead center to push the piston down. The objective of the impulse coupling is to delay magneto firing from 20o before top-dead-center until about 5o before Top-Dead-Center by building in a 15o lag angle into the magneto impulse coupling. This happens only in theory. The degree of impulse coupling retard is directly proportional to crank speed. Take for example the Lycoming O-235-L2C engine. The original starter cranked the engine too fast. Lycoming Service Instruction 1362 changed the lag angle of the impulse coupling from 15 degrees to 5 degrees to compensate for the fast turning starter and greatly improve starting on this engine. (with the 5 degree lag angle the engine may have a tendency to kick-back during hand propping. Don't hand prop!) A later starter (Prestolite MMU-4001R) was specifically designed to turn the engine slower. But be careful now, this slower starter works with the original 15 degree impulse coupling so the magneto impulse coupling lag angle should remain at 15 degrees. Now lets say you purchase a starter or magnetos for your O-235L2C engine. To get optimum starting performance you need to match the starter with the impulse coupling. The same hard starting problem may occur if you switch to a faster turning light-weight starter and don't change the impulse coupling on any impulse coupling magneto. 1. Magneto Impulse coupling not engaging. The engine with an impulse coupling will have a snapping sound while starting. The engine with a Shower of Sparks system will have a buzzing sound in the cabin whenever the starter switch is activated.
The absence of the clicking in an impulse coupling engine denotes a
problem with the impulse coupling. Snap impulse coupling. To check the timing
of the impulse coupling bump propeller to see where the impulse snaps.
To field check impulse coupling; Remove magneto with impulse coupling (usually
left magneto) from engine. Turn the aircraft magneto in proper direction by hand and
observe that flyweights in impulse coupling contact stop pins. If they
don't then flyweight axles are excessively worn and impulse coupling must
be replaced. If flyweights are in good condition, rotate magneto several
times to snap impulse and determine that impulse spring is not broken.
Impulse couplings used on Bendix magnetos are of two types: older style
riveted impulse couplings and newer snap-ring impulse couplings. Snap ring
type impulse couplings should have full engagement at 0- 125 RPM minimum
(D6LN-3000, D6LN-2031 at -75 RPM). Full disengagement RPM is 450 maximum.
2. Technique. 3. Flooded or over primed. The presence of a strong fuel smell in the exhaust pipe may indicate a flooded engine. Crank engine with throttle full open and mixture in idle cutoff. Letting the engine sit for awhile also helps get rid of excessive fuel. Continental TSIO-360 engines take a seemingly excessive amount of prime to start. 4. Throttle valve open too far. Set for approximately 800 rpm. An exception to this rule is carburetors without accelerator pumps such as the Bendix Stromberg. Start with the throttle closed. Without an accelerator pump, nothing happens when you open the throttle except you don't get the idle circuit. Opening the throttle reduces fuel flow and increases air flow to the engine creating a lean start mixture. The closed throttle allows the idle discharge tubes to flow fuel and limits the air. This enriches the mixture which is easier for the ignition system to ignite. With 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. 5. Insufficient/ too much prime. May be accompanied by backfire (inlet charge combustion). Make sure primer is not leaking. Primer nozzles may be clogged. These nozzles are so close to the intake valve that they carbon up. Not all the nozzles carbon up equally so one cylinder gets all the prime. When was the last time you had your nozzles cleaned? Take them out once a year and clean them. The Continental TSIO-360 engine take a seemingly excessive amount of prime to start. Make sure that the primer nozzle is indeed a primer nozzle and not a standard AN fitting. A standard AN fitting allows way too much fuel into the cylinder. This can cause difficult starting in cold weather. 6. Defective spark plugs or ignition wire. (not very likely) 7. (Shower of Sparks -Bendix system) Low voltage at vibrator input. Measure voltage between vibrator terminal marked "in" and ground terminal while operating starter. Must be at least 8 volts on 12 volt system, or 13 volts on 24 volt system. 8. (Shower of Sparks) Defective vibrator. If voltage is accept- able, listen for interrupted buzzing of vibrator during starting. If no buzzing is heard, either vibrator is defective or the circuit from the output terminal on the vibrator to the retard contact assembly is open. Check both switch and retard circuit. Check for 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. 9. (Shower of Sparks) Retard contact assembly in magneto not operating or dirty retard contacts. If retard breaker points don't open - you'll get no spark at all and no start. If the retard breaker points don't close, you'll be cranking with a fully-advanced boosted spark and may get a kickback. This would occur if the wire to the retard breaker is broken, or had a poor connection at the magneto. Retard points may not be closing due to improper adjustment or may not have a good electrical connection in the circuit. 10. (Shower of Sparks) Vibrator and magneto not putting out. Disconnect starter and all spark plug leads. Turn engine in normal-run direction until retard point opens at #1 cylinder firing position. Hold #1 plug lead approximately 3/16" from ground. Energize vibrator by turning switch to start. Plug lead should throw a shower of sparks to ground. If spark is weak or missing, replace vibrator. Check magneto for correct internal timing. Proper duration of shower of sparks may be checked by holding switch in "start" position, and hand turning prop until sparks stop. Degrees of prop rotation may be estimated to determine if retard points are adjusted properly. 11. Starter switch wired backwards. Starting on right magneto instead of left. The left magneto is usually the impulse magneto. The starter switch must be 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. On a Lycoming aircraft engine this sometimes breaks the starter housing. 12. Magneto improperly timed to engine. Advance breaker out of adjustment. If you know that the magneto is firing but the engine isn't then suspect that the engine to magneto timing is 180 degrees off. 13. Magneto internal timing not adjusted properly or "E" gap drifting because of point or follower wear. This is a common problem with magnetos that have not had routine maintenance. Especially on Slick magnetos, check for cam wear.
14. (Shower of Sparks) Retard points opening too late. 15. Low voltage to starter causing slow turning starter. This is more common on 12 volt light-weight starters which require a LARGE amount of current to get turning. Bad battery cables and poor connections are usually the problem. Burned starter solenoid points will cause a voltage drop across the solenoid. The best way to check a solenoid is with a load applied. When dealing with high current circuits, a fraction of an ohm is enough to produce poor, or no operation. Checking the circuit without a load would take a resistance of anywhere from a few hundred ohms to thousands of ohms to show a 0.2 volt drop. 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. Any more than 0.3 volt drop, replace the relay. Check battery capacity. Check condition of starter and battery
cables. Check battery condition by placing a digital multimeter across
the battery while someone cranks the starter. Battery voltage shouldn't
drop more than 2-3 volts. More than this and the battery is weak. Check
the voltage drop at the starter by measuring the voltage between the starter
power terminal and ground while someone cranks the starter with the mixture
pulled (so the engine doesn't start). There shouldn't be more than 3 volts
drop between the battery and the starter. If the voltage gets to the starter
but the starter cranks slow then suspect the starter.
16. Faulty ignition switch causing intermittent grounding.
17. Magneto distributor electrode finger loose or burned . 18. Magneto distributor block electrode burned. 19. Spark plugs fouled. 20. Spark plugs ice bridged. Occurs after a balked start in freezing weather. 21. Lycoming engines. Noisy start, failure to engage or sluggish start can be caused by a dirty Bendix Drive. The Bendix Drive on the starter is what engages the starter ring gear. It must be able to slide on the starter shaft to engage. Oils should never be used on the Bendix Drive or shaft because they collect dirt and become gummy causing the Bendix Drive to stick. Lubricate the shaft and drive with a silicone lubricant. Some models of light-weight starters such as the SkyTek do not use a Bendix Drive. 22. HIO-360-F1AD engine. Comply with Lycoming Service Instruction 1419 that allows using a harness that fires all the top plugs on the left magneto. Engines that fire all the bottom plugs on the left magneto can be hard to start especially in cold weather due to the possibility of plug fouling. 23. Engine not getting fuel. Fuel injected engines, fuel manifold valve (spider valve) stuck open. Check to make sure you are getting fuel to the nozzles. Then check to make sure fuel is going to the manifold valve. Fuel manifold valve incorporates a diaphragm and valve assembly, 20 micron filter and spring. If the valve assembly sticks, open fuel is not allowed to flow to the nozzles. If manifold valve vents back to the fuel tank, make sure vent system is not clogged. A clogged vapor return line may prevent proper action of the diaphragm and prevent the engine from starting. Bad fuel or no fuel are also causes. Fuel Starvation on Lycoming engines using mechanical (wobble) fuel pumps. A common cause for this problem is fuel starvation due to improper installation of the fuel pump. Make sure that the fuel lines are not crossed; that is, the inlet line should be connected to the inlet side of the pump (marked "IN" on the top of the port) and the outlet line should be attached to the fuel pump outlet port. Fuel should be present at the inlet side of the fuel pump. Improper installation of the fuel pump may result in a misalignment of the operating lever with the operating plunger in the accessory case. If so, there will be no movement of the lever and no pumping motion to provide fuel flow. If misalignment is found upon removal of the pump, the lever is probably damaged or broken. 24. Fuel vaporization. After an engine is shutdown, the temperature of its various components begins to stabilize; the hotter parts such as cylinders and oil cool, while other parts heat up due to the lack of air flow, heat conduction, and heat radiation from those parts of the engine which are cooling. This heat soaking is worse from 30 minutes to one hour following shutdown. During this time, the fuel system will heat up causing fuel in the pump and lines to "boil" or vaporize. During subsequent starting attempts, the fuel pump will initially be pumping some combination of fuel and fuel vapor. Until the entire fuel system becomes filled with liquid fuel, difficult starting and unstable engine operation will be experienced. 25. Lycoming O-320 H series engines. Hard starting or failure to develop normal static rpm during HOT weather can be brought about by an accumulative build up of dimensional tolerances that transfers pressure from the magneto drive gear to the impulse coupling. This causes the magneto to operate in the retarded position. Should this situation develop it can be confirmed by first making sure the ignition switch is in the "off" position. Then pulling the propeller through by hand several revolutions and listen for the audible click of the magneto impulse. If the audible click is not present, remove the magneto and replace the magneto drive gear with a new drive gear p/n LW-15659. When hand propping, stand clear of the propeller, Always assume the engine may inadvertently start. Refer to Lycoming Service Instruction 1360 for additional details. 26. Continental IO-470 45 degree lag angle on impulse coupling. Conversion to 30 degree lag angle per Bendix Service Bulletin 514 or Continental Service Bulletin M63-7 dated April 11, 1963 27. Defective magneto coil. Short in secondary coil windings will lower voltage output of coil thereby increasing coming-in speed of magneto. see Testing the Magneto Coil
Short in secondary windings starts out hidden inside the coil. As the wire shorts it lowers the number of turns in the secondary windings thereby lowering the voltage. It also causes heat and eventually burns till it reaches the surface. Small crack with black soot is a sign of internal coil burning in the secondary wire windings. Firing the magneto without spark plugs attached or with severely worn out spark plugs increases voltage stress on the secondary winding insulation and can cause the coil to fail. Note: There may not be any outward signs of damage until enough damage accumulates. 28. Weak magneto system. Not all magneto's and harnesses are created equal. For high compression engine, fuel injected engines operated in hot climates, the magneto, harness, and spark plugs used on the engine should be selected for maximum energy delivered to the spark plug. Contact Sky Ranch for specific recommendations. 29. Worn oil deflector on Bendix S20/200 series magneto. If deflector is loose it can walk up magneto shaft and interfere with impulse coupling flyweight. If you turn the engine over and don't hear the impulse couplings snap then check the oil deflector (slinger). 30. Incorrect magneto on engine causing incorrect impulse coupling lag angle. 31. Incorrect distributor cam on Bendix magneto rotor. Verify correct by checking "E" gap timing. 32. Magneto points not opening. Caused by worn or melted magneto cam follower. This can result from point overheating caused by insufficient capacitance in the magneto primary circuit; e.g. a defective magneto capacitor. 33. Bad Starter. If the starter is the old Delco or Prestolite style, remove the cover band and inspect the brushes and commutator. The brushes should form good contact with he correct brush spring tension. Inspect the commutator for dirt, burned bars, or high mica. The mica should be undercut to a depth of 1/32 inch. High mica prevents good contact between the brushes and the commutator. Burned bars on the commutator may indicate open circuited armature coils which prevent proper cranking. If the starter has low speed but high current draw then:
If the starter has high current draw and no speed then:
If the starter doesn't draw any current then:
If the starter has low speed and low current draw then:
If the starter has high free speed but low developed torque then:
34. Bad magneto capacitor. For engines using Bendix D2000/D3000 magnetos see Continental Service Bulletin CSB 662A dated 01/24/00. Subject deals with capacitors that may develop internal faults. 35. Won't start while cranking but starts when you let off of the starter switch. Lycoming engines with Bendix D2000/D3000 magneto with Shower-of-Sparks ignition. Engine may kick-back
|
Copyright 2003 by
Sacramento Sky Ranch Inc. All rights reserved. Prices subject to
change without notice. Not responsible for typographical or misprint. |
Impulse
coupling with broken pawl rivet.
The
cam follower on Slick magnetos is a piece of plastic inserted into the rotating shaft that bumps
open the points twice per revolution. As this wears the points open later and
don't open as much. This changes magneto to engine timing and weakens the spark.
A replacement point kit includes a new cam follower.
Bendix magnetos use a
sintered iron cam follower that are pourus by design to absorb lubricant. Normal
is on the right. The cam on the left is shinny - a sign that it is worn out and
not longer able to absorb oil.
10-357290-1
Bendix magneto switch
Magneto
distributor gear showing electrode finger
LW-15472
fuel pump
