Thoughts On Compression Readings

[GeneralT001]

Hi,

Looking at buying this aircraft with the following engine info, including the latest borescope:

2769.3 TTE

1253.5 SMOH

Cyl 1 - 64/80

Cyl 2 - 60/80

Cyl 3 - 40/80 (leaking compression at rings; slight pitting

Cyl 4 - 73/80

 

Not sure what was done on the "SMOH". Not sure if there is an oil analysis available but will check. If the oil is fine I'm guessing most likely need to pull the cylinder head of #3 and replace the rings? Engine produces full power.

Cost of repair?? Maybe $3,000?? for the one cylinder?

Is that time pretty much at the end of the engines life?

[AndreiC]

What engine are we talking about? Lycoming, Continental? If Lycoming, is it the IO360 (angle valve) or O360? Need more information.

As an aside, for airplane engines the heads are integral to the cylinder, so you are talking about pulling the whole cylinder.

It would also be very helpful to know how much the engine has been run in the past year. If the engine has sat a long time, and there is no other indication of rust (camshaft, lifters) the compressions could come back up quite a bit after running it for a while on the ground, to clear surface rust. Also, honing the cylinder and re-ringing the piston is not a very expensive affair. 

1253 SMOH is not the end of engine life. If it is not making metal you are roughly 2/3 of the way to a new overhaul (2000 hours). Also could depend a lot on who did the overhaul and how much they actually did (but you said you don't know this...)

[GeneralT001]

3 minutes ago, AndreiC said:

What engine are we talking about? Lycoming, Continental? If Lycoming, is it the IO360 (angle valve) or O360? Need more information.

As an aside, for airplane engines the heads are integral to the cylinder, so you are talking about pulling the whole cylinder.

It would also be very helpful to know how much the engine has been run in the past year. If the engine has sat a long time, and there is no other indication of rust (camshaft, lifters) the compressions could come back up quite a bit after running it for a while on the ground, to clear surface rust. 

1253 SMOH is not the end of engine life. If it is not making metal you are roughly 2/3 of the way to a new overhaul (2000 hours).

Hi,

It is an O 320. Flown about 150 over the past 2 yrs.

Edited Sunday at 04:54 PM by GeneralT001

[AndreiC]

Just now, GeneralT001 said:

Hi,

It is an O 320.

Oh, so we're not talking about a Mooney? Only the original M20 (no letter) had the O320, and those should be bought only by museums -- they still have the wooden tail I think. Or maybe also some M20A's, with just the wood wing?

[takair]

For a Lycoming I would be suspicious of numbers drifting below 70.  #3 definitely requires attention, but 1 and 2 are getting there too.  What kind of airplane?  How are you measuring full power? Even engines with worn cam lobes are hard to measure until a high DA takeoff doesn’t yield good results….which leads to the next thought….if pitting is seen in the cylinder, then the cam deserves a look when the jug comes off…. This engine might be talking to you…

[GeneralT001]

Thanks everyone. Its a Long Eze and I think I'm just going to pass on it as the thought of a major overhaul in the near future seems very likely and very expensive no doubt.

[Utah20Gflyer]

I think the first thing I would do is fly the plane and do the compression readings again.   You might find that cylinder 3 “repairs” itself.   My understanding is that cylinder compression can change drastically from one test to another.  The result is also dependent on getting the engine up to proper temperature and mechanic technique.  Overall a pretty subjective test.  
 

A cylinder will make full power at 40/80 so the real issue is usually oil consumption.  If the engine is using a lot of oil that is a much more reliable indication that there is a problem with the rings.   Sounds like this is a prebuy situation so you would be relying on the owner to tell you the truth about oil consumption.   I would fly a 60/80 cylinder without a bit of hesitation as long as oil consumption is reasonable. 
 

If a cylinder is pitted then the cam could be pitted too.   That would be the reason for a premature major overhaul and unfortunately that is very difficult to evaluate in a prebuy situation.   If cylinder #3 did come off you could take a look at the cam, but cylinder removal is a pretty serious ask from a potential buyer. 

[A64Pilot]

I’d pass myself mostly because it’s an Experimental, unless I knew who did the overhaul and exactly what parts were installed.

There are a whole lot of Experimental's flying around filled with unairworthy parts. Used to be mostly airboats but heck even airboat motors end up in Experimentals now.

Some of the best aircraft I’ve seen were Experimental’s, but there are many very questionable ones, especially older ones like I bet the Long-ez is.

Problem with buying an Experimental is in truth you need to have at least A&P level knowledge or have a very good friend that is an expert in the type

 

Edited Sunday at 10:38 PM by A64Pilot

[Pinecone]

I was talking to the shop that maintains my CAP-10 one day.  He had a couple of engines apart.  One was going out for rework.  Somehow, he got to telling me about a crank he had taken out of an engine due to being worn beyond limits.  It sat in a corner for a year or so, then some guy in the experimental world asked to buy it.  Shop guy told him it was worn beyond service limits.  No problem, guy still bought it.

So, I wonder where that crank went????

[A64Pilot]

7 minutes ago, Pinecone said:

I was talking to the shop that maintains my CAP-10 one day.  He had a couple of engines apart.  One was going out for rework.  Somehow, he got to telling me about a crank he had taken out of an engine due to being worn beyond limits.  It sat in a corner for a year or so, then some guy in the experimental world asked to buy it.  Shop guy told him it was worn beyond service limits.  No problem, guy still bought it.

So, I wonder where that crank went????

I suspect that quite a few cranks that were removed during the AD’s years ago are flying again too.

[MikeOH]

2 hours ago, A64Pilot said:

I suspect that quite a few cranks that were removed during the AD’s years ago are flying again too.

Which begs the question: How many of those have failed in flight?

[Paul Thomas]

8 hours ago, Pinecone said:

I was talking to the shop that maintains my CAP-10 one day.  He had a couple of engines apart.  One was going out for rework.  Somehow, he got to telling me about a crank he had taken out of an engine due to being worn beyond limits.  It sat in a corner for a year or so, then some guy in the experimental world asked to buy it.  Shop guy told him it was worn beyond service limits.  No problem, guy still bought it.

So, I wonder where that crank went????

A bad crank and bad case can still be a good value. They are great to use when building an airplane; you can build the cowl just right with that "dummy" engine. It easier to get the space between the spinner to cowl and perfect.

[A64Pilot]

19 hours ago, MikeOH said:

Which begs the question: How many of those have failed in flight?

Who knows, AD’s are very often tripped by very low probabilities if the possibly severity is high, very few of the wing spar inspection AD find bad spars, but it only takes one to kill you.

Plus and as an ex manufacturer who rode the bust and boom that aviation can be a little bit of me wonders how much AD’s can be a profit model. AD’s differ from Auto recalls for example in that first they are mandated and secondly most often the owner shoulders the expense. Having to produce a large number of parts to cover an AD is an increase in business after all. But it also come at the expense of the way purchasers may view the product.

But AD’s are very often the coffin nail for a manufacturer too, especially if they try to “do the right thing” and shoulder a large portion of the expense.

Finally and again speaking from having been a manufacturer myself for 15 years, it’s my opinion that Lawyers are often a large portion of the blame for AD’s.

A lot of decisions in aviation manufacturing are done based on the concern of litigation.