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Stumped. Cylinder drops out at High MP.

lifter

My money is on a collapsed lifter. Cue post #21 (Andy Cobb). I had a similar problem with a Superior-built engine, though the intake lifter on my offending cylinder never completely collapsed. I datalogged several flights, then reviewed the data on savvyanalysis.com and eventually deduced what was going on. Replacing the intake lifter guts solved the problem. Given how easy it is to swap lifter plunger parts on the average Lycoming I'd start there.
 
I suggest measuring cam lift, if thats good, I would swap out lifter hyd units.

Is this thing constant speed or fixed pitch?

Three pages in, no mention of RPM change, just MP change. Lifters don't care about MP.

Actually, as MP increases, the mass of the charge and total pressures will increase. That means at the end of the combustion cycle blow down pressures will be higher at higher MP. The lifter forces at opening will be higher as the valve initially lifts against the pressure in the cylinder. A changing force on the lifter definitely connected to MP.

I have sent the spider/flow divider off to AFP for them to re-check its function. Given my general understanding of how it works, and the testing done so far, I have no hope that there is any problem there especially after moving lines and ports and injectors and injector inserts around.

I completed a check of the cam, lifters, and dry tappet clearance per service bulletins and everything is within spec except the exhaust dry tappet clearance was slightly in excess (about .005) of the .080 allowed. Ill be installing a longer push rod as soon as I find one just to rule that out but I also dont have any faith that it would cause this problem.

Im still at a loss and Im still scratching my head. ARGH! Thanks for all the help and ideas so far.

:confused:

I could imagine a scenario where an internal component was cracked in the lifter and higher forces creating higher pressures and caused a leakage not normal seen. It seems rare, but possible. Not really sure how to test the theory on an actual lifter, except replacement, or swap to another cylinder, as this is a very dynamic situation.

Not saying this is a smoking gun, but it is physically possible to be related to MP.
 
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Sorry if I missed it, but have you replaced your plug wires on the suspect cylinder? Not checked - replaced. Much cheaper and easier to address - and probable -
than lifters. Ignition wires can do strange things when damaged.
 
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Mike, did this start happening after you changed your ignition?

My thinking is that you could have a "leak" on the ignition wire at high power settings.

(We have seen this with the P-mags and only caught it because the EICommander shows the discharge of the plugs. Turned out the owner had moved his wires and one was touching his engine mount and was occasionally shorting through the insulation to the mount.)

Also a bad connection could give you the same symptoms.

Good luck!
 
Sorry if I missed it, but have you replaced your plug wires on the suspect cylinder? Not checked - replaced. Much cheaper and easier to address - and probable -
than lifters. Ignition wires can do strange things when damaged.

I just saw this after my post, above. I agree 100% with Low Pass. Easy to check and fix.
 
I have sent the spider/flow divider off to AFP for them to re-check its function....I completed a check of the cam, lifters, and dry tappet clearance per service bulletins and everything is within spec except the exhaust dry tappet clearance was slightly in excess (about .005) of the .080 allowed. Ill be installing a longer push rod as soon as I find one just to rule that out but I also dont have any faith that it would cause this problem.

Hey Mike, got an update?
 
Dry tappet clearance on #1 exhaust was high. Got a longer rod #37. Still slightly high at .097. Spider came back fine. Lifters test fine. Suspecting the cam. Engine coming off for teardown and likely complete rebuild by my trusted engine man JB Aircraft Engines out of Sebring Fl. with 1800 hours on the engine, and new cylinders, new ignition, new FI, gonna be a might as well do it all. Argh!
 
Tear down findings?

We?re there any findings during the tear down by the engine shop? Was that cam wiped? I ask because my engine is doing something similar and has since at least hour 1.5. Thanks.
 
Ahh yes. Sorry about not responding. Yes the cam was junk. I chased this problem for a long time. Ended up with a full tear down and rebuild. JB down in Sebring at JB Aircraft Engines did the honors. Runs great at solved all the issues I was having.
 
Thx

Ok, thx, your symptoms were a little different than mine, but close enough to be interesting.
 
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