Engine misfiring

rough
engines
vanagon
volkswagen

#1

This isn’t exactly a car question but it could be. My Lycoming horizontally opposed engine (sort of like a Volkswagen’s) has two magnetos; each has points and condenser just like a regular distributor. In flight the engine is not running as smoothly as normal. We found “burn” marks on the condenser, pits on the side of the points, and a rich plug tip on the cylinder connected to that magneto. We are waiting for replacement parts now. My question: would these issues possibly cause a “miss” in the engine manifested by rough operation or vibration? (I used VW Vanagon as my model as an illustration only.)


#2

Definitely. The failed ignition components likely caused the appearance of rich running on the plug for that magneto. Change out the bad ignition parts and see what happens.


#3

I think airplane motor maintenance is a whole new ballgame. Your ignition issues need to be resolved, but certainly burned points would cause misfires and rough running. It seems to much current could be going to the points which might be a condenser issue. Two magnetos is a safety issue, it keeps 2 cylinders firing if one magneto and ignition fails.

My concern with an airplane motor is did the misfires cause any valves to be “burned” or other internal issues for the motor. I’m sure your mechanic can advise if a the motor needs more work to be air worthy.


#4

Trial and error testing on an airplane is difficult. I feel certain that there is a maintenance schedule for the ignition system. Is maintenance up to date? Are the magnetos redundant? Does the engine have 8 spark plugs?


#5

Pitting and metal transference from one side of the contact points to the other side is generally caused by an incorrect or failing condenser, all depending.
Yes, it can cause a misfire and I’d replace the plugs also.

(Note that a weak condenser can actually mimic a rich fuel/air mix and can cause an engine to cough black smoke)


#6

Thank you all very much for your responses. They all made sense. I am waiting for new magneto parts (points and condensers). I will post the resolution here just for your interest. Incidentally, with regard to a horizontally opposed piston aircraft engine, each of the two magnetos provides spark to one spark plug in each cylinder; there are two spark plugs for each cylinder for redundancy. The engine will run (maybe a little rough) on just one set of plugs powered by just one of the magnetos.

CaptainBob


#7

You might be wise to ohm the plug wires. And, you must re-time the engine when the points are installed.


#8

Thank you for your note. The plug wiring harnesses are new; and the mags will be timed once the new condensers and points are installed (we are still waiting for the parts from Dallas.

CaptainBob


#9

I would strongly suggest that an aircraft mechanic certified for reciprocating engines inspect the engine before leaving the ground. “New” does not necessarily mean good. A plug wire, or any part, could be bad out of the box. Properly maintained aircraft should never have pitted points. Scheduled maintenance should replace them long before failure.


#10

Using 80 year old ignition technology seems a little strange today…The only benefit, no source of electrical power is needed in the aircraft…But don’t virtually all aircraft now have a battery and a charging system to power lights, radios, instruments and the like? Those old Lycoming and Continental engines MUST have electronic ignition systems by now…Why beat your head (and your wallet) against the wall with those mags??


#11

Thanks again. The wires checked okay. My mechanic is the best I’ve had after 47 years of business and professional flying. I have full confidence in him; however, he will be along for the ride after everything is put together.

Captain Bob


#12

Thanks for your note. Yes, the A/C has an independent electrical system. The engine will run fine with the electrical master switch off. With regard to electronic ignition, I’ve never heard of this for a Lycoming reciprocating engine. I’ll ask about it later today.

Captain Bob


#13

As promised, I followed up today with the I&A at the airport.There is, indeed, an electronic ignition module for Lycoming engines, similar to auto electronic ignitions (I installed one myself years ago in my 356-C Porsche without any problems. The aircraft electronic ignition system essentially functions as a “Master” to the magnetos, sending instructions to the mags with regard to variable spark timing depending upon engine demands. The systems are made by Slick (a traditional magneto manufacturer). I understand it is pretty expensive and may not be cost-justifiable in many instances. Anyway, we both learned something today.

Thank you for your help.

Captain Bob