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Lycoming Engine Timing

Southern Airboat Gallery Archives

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Narrow roads
Stupidity1
9-5-2006-07
Old Swamp Buggy..
IMG_0892
M

marshmaster pat

Well-known member
Question for anybody that plays with Lycomings.

I know that the timing on the lycoming engines (540s) is between 20 to 25 degrees. However, there is one of the guys I know over here that is turning his timing up to between 30 and 33 degrees. He is running a parallel valve engine - standard pistons, but seems to be able to turn up that motor to about 3100-3200+ with a wooden prop. I had the same pitch prop and could only get 2800 max with an angle valve engine before switching to composites. He turned up over 3100 with my old wooden prop. I have excellent compression and the motor purrs with less than 200 hours.

I know that increased timing can increase operating temperature which can be bad and may cause predetonation, but what about with a lycoming. I know the A&P guys are scared of any potential predetonation.

Anyone have experience with this. The extra RPMs would be nice at times to get unstuck, but not if it costs a motor.

Thanks
 
A couple degrees of additional timing will not make a motor turn 300 more RPM under a load. it takes a 50 horse nitrous kit to raise 300RPM’S under a load. His motor is just making more power my guess with only a limited bit of information is generally the more cylinder pressure you have the less timing you need to run so if he has less cylinder pressure and runs more timing and still makes more peak power. I suspect a cam may have been changed. A larger cam generally reduces cylinder pressures and creates more peak power. I’m just guessing though. If he is a buddy talk him into doing a compression test in front of ya play stupid and ask him what kind of numbers you should have. There is something different in his motor it could be ring seal, valve seal, compression, stroke, but if he makes less cylinder pressure than you but makes more peak power I bet it’s the camshaft.
 
Waterlizard - you must me right, was talking to a buddy that was helping us when we were trying different props one day. He said my old prop would only turn up about 2900 at best on the other boat (He thought is was about mid range 2800s). I was also told the other boat's wooden props were 68 or 70 inches while I was turning a 72. That would explain a few things.

Cracker - Thanks for the link. Have seen that before, but I have noticed to get most lycomings up to what they say is best thrust, you are turning about 300 to 500 RPMs above recommended.

Not sure it is a problem, but I know a brand new Cessna owner that is in a legal fight with Lycoming about his motor over revving on the taxi-way while cycling his prop. All the A&P guys freak when you talk about turning up above 2900. So I get worried because I am very ignorant.
 
Sorry, I thought you ran the exact same prop on both motors well that explains that.
 
Pat,

Take a look at this article:

http://www.sacskyranch.com/detune.htm

It explains part of what the A&P guys are worried about. Aviation is all about limitations and procedures.

I would think the lightweigt props would help crank life, but the throttle jockeying does not help.

Jim
 
Waterlizard - I thought the props were the same, but my buddy swears that the other boat's were shorter. Since he was holding the props as they were changing them, I will not argue. I was busy installing the new composite.

Cracker - thanks for the links
 
Pat,

I'm real curious to know just how much timing/rpm your friend is using on a regular basis, and if there have been problems.

Jim
 
The aircraft crank shaft counter weights perform the same function a harmonic balancer does for a car motor. It decelerates the torsional twisting of the crank shaft from power pulses. What’s neat is in the late 70�s and early 80’s Mororso manufactured a harmonic balancer that worked on the same principal as the aircraft system does. Mechanically they were very similar. So far the broadest RPM race balancer out there is a TCI rattler which uses weights similar to the aircraft. That fly out centrifugally according to engine RPM.
 
Jim,

I thought he said the timing was up around 32 to 33 degrees. He typically runs cruise at between about 1700 to 2200 RPMs. But I don't trust my memory these days due to young kids keeping me up at night.

I will chase him down over the next few days and ask then let you know.

pat
 
Pat,

I love to see some innovation and pushing the envelope. That's how we learn.

Jim
 
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