Lower compressions at recent annual

[Jeff Holzaepfel]

I am considering purchase of a Twin Comanche and have been studying the engine logs. The engines wer overhauled by Mattituck in 2000 after being in service about 3,000 hrs and change. I have not seen complete logs yet and do not know if this was the second overhaul or if the first run actually took it that far with a top overhaul or something.

It has been flown only about 350 hours up to 2013, at which time the new owner (current seller) had them both cracked open and inspected by a mechanic, who replaced one of the camshafts with a "freshly ground" camshaft, among a few other odds and ends replaced or reconditioned.

What is also interesting is the recording of compression checks, which started out in the 78/79/77/77 range in 2011 and in 2016 now read 72/72/72/72.

Besides the fact that there are few hours on the engines in such a lengthy period of time, should I be concerned about these compressions?

And what is a freshly ground camshaft? Is that the same as a reconditioned camshaft?

Thanks,
Jeff

[N3322G]

Lycoming recommends O/H every 10 years or 2,000 hours. The pricing should reflect that.

[LeWayne Garrison]

First, a reground camshaft usually means the lobes were ground down to remove discrepancies. The actual lift and duration shouldn't change. I've seen it done with no problems, but I'm personally not a fan of it. Find out, if possible, what shop did the camshaft work, and check their reputation. New cams as part of an overhaul "kit" are competitively priced. Lycoming has a service letter concerning it, but remember Lycoming is in the new parts business.

As to the compressions. Those compression readings are very good. Compressions will change every time they are checked. I would have no worries about those readings, especially if the check was done on a cold engine.

The overhaul hours and calendar time have absolutely no bearing on a Part 91 operator. They are suggestions (and not very good ones) at best. Remember Lycoming is in business to sell engines and parts. As noted yourself, these engines sometimes make 3000 hrs between overhauls. The average hours per year between 2000 and 2013 is about 26 hours per year. While low, it is not ridiculously low. Most of the annuals I do now have between 25 and 60 hours yearly. Do keep in mind, however, that engines that make 3000 hrs are usually flown regularly (but not 200 hrs per year).

One thing that concerns me is why the engines were "cracked open" at 350 hours. Unless the current owner was suckered by an unscrupulous A&P there would need to be a reason to tear down two engines. From what you described, I would guesss (and it's only a guess) that one engine "made metal" from a bad camshaft and needed to be torn down. That's why the reground cam. Why the other engine was torn down is a mystery, but may have been an overzealous owner or A&P convinced that because one engine had a problem, the other one would also.

Study the logs carefully and try to read between the lines and ascertain logical explanations for maintenance done. From the small amount you posted, I would not be afraid to pursue this aircraft further.

[Clarence Beintema]

Lycoming SI1009 recommends a 12 year overhaul life along with an hourly time which can be extended for high use engines. For a private aircraft these do not apply.

Camshaft failures in Lycoming engines are among the most common, new and reground fail with regularity. The other engine may have had a simple cylinder pull for inspection based on the other engine with a bad camshaft. The owner, the logs and the A&P should be able to clarify.

Clarence