Schweizer 300 C

[HeliFrank]

We have a problem with our 300 C. It had a fresh 300 hours inspection approximately a month ago. We flew the aircraft for an additional 40 hours after that. Then one day when returning from flying, cooling down and disengaging I realized erratic fluctuations in ERPM when the RRPM came down to @ 100 RPM followed by the engine quitting. At first I thought that the mixture might have been too rich as we had a pretty warm April.

As the engine only seemed to be affected when running without load (in idle after returning from the flight) we continued to fly until the following 50 hours inspection was due. The mechanic adjusted the mixture, increased the idling RPM a litlle bit and everything seemd to be ok.

Now @ another 5 hours later the situation seems to be worse than before. After cooling down and disengaging the rotor everything seems to be normal. The engine is idling at 1400-1500 RPM, rotor RPm is decreasing and when reaching @ 120 RPM the engine just quits without any prior hints.

Temps, pressure and power is normal´and during flight everything seems to be normal. I think that either

• the fuel system (nozzles)
  

• or maybe the installed overspeed limiter
  

is somehow involved.

 

Any other thoughts???

 

 

PS: Yes, the aircraft is grounded until Monday and until the mechanic shows up

[Fastlane]

Not exactly sure what the problem is. It could be MANY things, EGR system, fuel issues, burnt valve, broken piston ring, temps, etc etc.

 

Two things I am 100% sure of, I'd be on the phone with Lycoming! And in a hurry! And Second, GROUNDED!

 

I'm really curious how this turns out, please let us know what you find.

Edited May 24, 2007 by Fastlane

[Guest pokey]

i dont know anything about the RPM limiter, i never even seen one, but? if yous suspect it, disconnect it. I've had problems with the fuel servo s tho, if you have access to a known good servo, try switching it---those things are very expensive to overhaul. I've had hi-power engine mis-fires due to a dirty fuel injector nozzel, but i doubt that is you problem since the engine quits. I doubt its electrical either. A far as it being anything mechanical in the engine?--i highly doubt it, but you DID do a compression check right?

[choppedair]

Just an idea. I don't recall what RPM the engine idles at, but is it possible that the clutch isn't disengaging fast enough, and the rotor is actually dragging the engine down when you set it to idle?

[HeliFrank]

Two overhauls on our own injector, one injector in exchange, a new set of spark plaques, replacement of the gaskets at the inlet tubes, replacement of one inlet tube (had a small crack at the very end), x-checking of the ignition harness, replacement of both magnetos (lucky us, we had our own ones on stock), double checking that the clutch would disengage all the way (thanks choppedair), two compression checks (one warm, one cold one) etc. etc. etc it looks like everything seems to be fine now.

 

Solution: Probably one of the drain valves at the bottom of the sump always got stucked open at operating temperature allowing for some additional airflow at idle (when the valves should be closed). We replaced both valves, engine is running fine now.

 

Feels good to fly with an engine which seems to have been through a major overhaul... ;-)

[apiaguy]

Thanks for the Update!!

 

I hate those pesky little problems..... for such a simple engine when you have a masked problem it is very frustrating.

 

Those dang bendix fuel injectors are classic for the suspected problem. I had a 269 ship years ago that I had a similar hard to find problem with the engine after overhaul... turned out to be 2 bad spark plugs (all were new) But I spent alot of time flow testing that servo.

 

Anyway, glad you got it smoothed out....