Does an overhaul un-lemon an engine?

If an engine has been overhauled 3 times, never making TBO either time
(not even making it to 1/2 of TBO 2 of the times), should I be concerned
that it might be a lemon, or if the current overhaul was done right and
the engine has been treated right since then, should I not worry about
how it did before this overhaul?

On 5/9/2005 09:56, xyzzy wrote:

If an engine has been overhauled 3 times, never making TBO either time
(not even making it to 1/2 of TBO 2 of the times), should I be concerned
that it might be a lemon, or if the current overhaul was done right and
the engine has been treated right since then, should I not worry about
how it did before this overhaul?



That's a really good question. Do you have "The Complete Overhaul"
by Kas Thomas? This is a really good book on the overhaul and industry.

Basically, the engine is a collection of parts. Some of these
parts can be replaced during the overhaul. If the cylinders, crank,
cam, etc. are replaced, is it the same engine?

Additionally, these replacement parts came from somewhere. Perhaps
the "new to you" crank comes from an engine that was having all
sorts of problems.

Basically, if the parts all meet tolerances, the engine should
perform as new. So I think the real question comes down to the
work done during the overhaul. Were the parts inspected as well
as they could have been. Was the resurfacing work done as well
as it should have been (or at all), etc.

Based on my reading only, that is what I think makes a good
overhaul. The book is chocked-full of doom and gloom, but is
really a good read - and an eye opener!

To determine why your engine didn't make it to TBO, you may
have to look at the shop that did the work (assuming the
engine wasn't mistreated, of course). Perhaps they have a not
so good reputation?


--
Mark Hansen, PP-ASEL, Instrument Student
Sacramento, CA

On 9-May-2005, xyzzy wrote:

If an engine has been overhauled 3 times, never making TBO either time
(not even making it to 1/2 of TBO 2 of the times), should I be concerned
that it might be a lemon, or if the current overhaul was done right and
the engine has been treated right since then, should I not worry about
how it did before this overhaul?


The keys, I think, are who did the current overhaul and to what standards it
was done.

If the work was done by a quality shop with a good reputation, that is one
encouraging sign. If it was slapped together by some obscure A&P working
out of his garage, that's another story.

But the real question is what standard was used to determine reuse or
replacement of engine parts. Many of the best overhaulers will not try to
reuse cylinders, although it's perfectly legal to do so. In fact, any part
meeting minimum service tolerances can legally be reused in an overhaul.
But a "premium" overhaul will only use critical parts that meet "new"
tolerances. Of course, the cost difference between the two extremes can be
huge, as can resulting service life.

--
-Elliott Drucker

Mark Hansen wrote:
On 5/9/2005 09:56, xyzzy wrote:

If an engine has been overhauled 3 times, never making TBO either time
(not even making it to 1/2 of TBO 2 of the times), should I be
concerned that it might be a lemon, or if the current overhaul was
done right and the engine has been treated right since then, should I
not worry about how it did before this overhaul?



That's a really good question. Do you have "The Complete Overhaul"
by Kas Thomas? This is a really good book on the overhaul and industry.

Yes! A big agreement on that. An excellent read for an owner.

snip


To determine why your engine didn't make it to TBO, you may
have to look at the shop that did the work (assuming the
engine wasn't mistreated, of course). Perhaps they have a not
so good reputation?

Maybe so, but I think there are some more important factors:
(1) luck, and
(2) operation technique (cold starts, high RPM starts, frequent or continuous
high CHTs. Against my religion, but some would say: shock cooling.

All just my opinion, of course, worth what you paid.

On 5/9/05 11:56, "xyzzy" wrote:

If an engine has been overhauled 3 times, never making TBO either time
(not even making it to 1/2 of TBO 2 of the times), should I be concerned
that it might be a lemon, or if the current overhaul was done right and
the engine has been treated right since then, should I not worry about
how it did before this overhaul?



Have you looked into how the engine was operated? If it's the same pilot,
maybe there is something to be changed there...

- Don
Predictions are hard to make, especially about the future.
- Niels Bohr

I would suspect the case may not be true. Had it been line bored, surfaces
planed, and re-doweled? If not, you may throw all the parts you want at it,
but it will eat them up anyway.
Jim

"xyzzy" wrote in message
...
If an engine has been overhauled 3 times, never making TBO either time
(not even making it to 1/2 of TBO 2 of the times), should I be concerned
that it might be a lemon, or if the current overhaul was done right and
the engine has been treated right since then, should I not worry about
how it did before this overhaul?

xyzzy wrote:
If an engine has been overhauled 3 times, never making TBO either time
(not even making it to 1/2 of TBO 2 of the times), should I be concerned
that it might be a lemon, or if the current overhaul was done right and
the engine has been treated right since then, should I not worry about
how it did before this overhaul?


The overhual isn't going to be the only factor in determining whether it
makes it to the next one. How it's used and maintained is. If you fly
infrequently and hardly do maintenance outside of annual time, there's
no way it's EVER going to make it to TBO. Our aircraft that get beat
to death by students regularly exceed TBO by hundreds of hours.

No Spam wrote:

On 5/9/05 11:56, "xyzzy" wrote:


If an engine has been overhauled 3 times, never making TBO either time
(not even making it to 1/2 of TBO 2 of the times), should I be concerned
that it might be a lemon, or if the current overhaul was done right and
the engine has been treated right since then, should I not worry about
how it did before this overhaul?




Have you looked into how the engine was operated? If it's the same pilot,
maybe there is something to be changed there...

In this case, it was first owned by a flight school that put 1000 hours
on it in 2 years and then overhauled it. Then it was sold to someone
who owned it for 40 years, went long stretches without flying it, and
went an average of 400 hours and 15 years between overhauls (including a
top). It was major-overhauled in 2003, about 40 hours put on, and then
sold to the current owners in 2004 who put about 50 on it in the last
year. I'm considering buying in with them. Sounds like the consensus
is that it's how good the last overhaul is, and how well it's been
treated since, that matters, and what it did before the last overhaul is
less important.

What's the engine?

Mike Granby wrote:

What's the engine?


Cont O-300