Lycoming Cylinder Work

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Thomas
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Lycoming Cylinder Work

Post by Thomas »

I have to make the decision to remove a cylinder to check the condition of the camshaft and the general state of the engine. My engine has 750hrs since new in 2003 means 14yrs …
My A&P recommend to remove Cyl #1 or #4 to inspect the engine.
I am a bit skeptical, to do this work with the engine “on wing” on field. Of course knowing that with this low yearly flying time it is a candidate for corrosion.
As an engineer myself, I tend to follow the “never touch a running system” philosophy.
The great expert, Mike Bush, made me even more skeptical.
https://www.savvyaviation.com/wp-conten ... afraid.pdf

What you think about this matter, have you done this work?
Thomas Bienz DA40-180 40.337 D-ENMA
Home Airport LSZC Buochs Switzerland
Antoine
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Re: Lycoming Cylinder Work

Post by Antoine »

Hi Thomas. I have some relevant experience with my second DA40 (N905PA) which I recently sold to another forum member. This aircraft was previously owned by a friend of mine who had lost his medical. It had been a hangar queen for a long time (maybe 2-3 years). It was only being ground-run on a regular basis.
Corrosion in the cylinders was not an issue. Compressions were at new level and stayed there in the 200 hours or so I flew with it.
We never bothered to remove a cylinder after seeing that oil was also ok and the engine was making enough power to make this the fastest DA40 I ever saw.
Also, even if you would remove a cylinder and find some corrosion that is not directly a structural issue, you can't really do anything about it, right?
So I think it is a wise idea not to remove the cylinder... it will save costs but more importantly it will not cause any additional risks due to the human intervention. Id' rather leave the highly stressed parts in the exhaust system alone if they are working fine.
Why don't you have the oil analyzed and look for any telltales of corrosion instead? You can always remove the cylinder if something is not right.
Safe flying. Are you back to Buochs?
A
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Chris B
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Re: Lycoming Cylinder Work

Post by Chris B »

Thomas wrote:What you think about this matter, have you done this work?
Hi Thomas -

As you know, corrosion & pitting on the cam is generally the weak link in the parallel valve Lycoming engines, and direct inspection requires cylinder removal. Our main defense is regular use, and there is some evidence that CamGuard helps. OTOH, unlike a failing valve, a spalled cam will not instantly grenade the engine, but should leave clues via inspection of the oil filter, oil screen, oil analysis & oil consumption trends. Borescope of the cylinders should also give some indication of obvious engine corrosion.

Has anything other than calendar time prompted your A&P's suggestion? Without some other indicator, I share your reluctance to pull a jug in the field, although maintaining a positive working relationship with your A&P is also valuable. One middle ground might include more frequent oil changes & inspections.

My engine just passed 2200 hrs, and I discuss this regularly with my mechanic. We plan to keep running the engine with regular borescope & various oil inspections until there is some evidence of a problem.

Chris
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Re: Lycoming Cylinder Work

Post by Thomas »

Hi Antoine,
thanks your advice.
I am only part time here in Buochs. Will soon be in FL again till April 18, so plan a LSZC visit with your bird spring/summer 18 (when you upgrade to a PC12 :)
Last edited by Thomas on Fri Nov 17, 2017 3:55 pm, edited 1 time in total.
Thomas Bienz DA40-180 40.337 D-ENMA
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Rich
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Re: Lycoming Cylinder Work

Post by Rich »

It sounds like what your mechanic wants to accomplish is to check the camshaft/lifters for spalling. When this happens you start to get sizable particles of steel floating around the engine which starts to do damage to things like bearings and cylinder walls. This condition happened to my plane and it resulted in $15K worth of engine semi-rebuild. The indicator is these particles will show up in the oil filter when it's cut open as part of the oil change. Once that starts to happen the engine does need to undergo teardown and rework or it only gets worse. But here's the deal with trying to determine this by partial teardown (i.e., pulling cylinders):

1. You need to pull at least two cylinders, as you can't see all the stuff you need to see with only one pulled, In my case the spalling was limited to two cam lobes and the three lifters they operated. If one looked through the "wrong" cylinder it would not have been visible.

2. If this spalling is detected, you get to have the engine pulled and reworked. Just as it would if these iron/steel shavings had appeared in the filter. So it doesn't really save you anything.

Oil analysis and filter inspection will show up problems early enough. In my case the stuff showed up in the filter, so they bore scoped the cylinders. Scoring showed up in #2, so they pulled it and confirmed the spalling in the camshaft and lifters.
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Re: Lycoming Cylinder Work

Post by Lance Murray »

Pulling a cylinder is major surgery. Why does your mechanic feel the need to do so? Is he following Lycoming's recommendation? I know of no inspection that requires pulling a cylinder. If you are doing this to simply inspect the cam shaft then I would say no. Don't do it.
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Re: Lycoming Cylinder Work

Post by Steve »

Thomas:

I'm not a big fan of major 'elective' surgery on the engine. My engine has a similar number of hours, is 2 years older. I do oil analysis and cut the filter every oil change. If something changes significantly, then what your mechanic suggests is reasonable.

I have a good relationship with my A&P/IA. We always discuss the options and I usually take his advice. When he said rebuild the prop, I did ($5K), even though there were no leaks or other indicators of a problem. One item where I didn't was fixing a small oil leak from a crankcase through bolt/cylinder O-ring. He said it wouldn't be a big deal, a couple of hours of labor (which I would mostly do under his supervision). I told him I would observe it, and consider repair if it got worse. It hasn't in about 3+ years, so I'm still observing (and cleaning off) the few drops that leak every 25 hours.

My Annual is coming up next month, so we'll see if he mentions it again...

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Re: Lycoming Cylinder Work

Post by Lance Murray »

Reliably obtaining recommended torque on an in-service motor is nearly impossible. Many mechanics don't seem to respect this fact. Variables like accessibility, bolt lubrication, bolt wear, bolt cad plating wear, etc all effect the torque. These things are controllable on a new engine or an overhauled engine with new hardware. They are far less controllable in an in-service motor. This is a big threat. The only accurate way to measure spring tension on a bolt is by measuring stretch on a new bolt. Unfortunately there isn't a way to do this on studs and through-bolts so we are stuck with torque and it's unreliable methods of measurement.

The point is that major surgery like this needs to be a last resort when all other methods of inspection have indicated that the cylinder needs to be replaced or the engine needs to be removed from service and overhauled.
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Re: Lycoming Cylinder Work

Post by Thomas »

Thanks to all for your advice, I will have a word with my A & P on Monday as we start the annual.
Thomas Bienz DA40-180 40.337 D-ENMA
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