Engine exceeds TBO

RST Engineering wrote:
snip

The other side of that coin is that bearing/crankshaft wear tends to become
exponential after a point in time when it departs from linear. That is, for
a long time (extrapolated by the manufacturer to be "TBO") the wear on the
bearings and the crank is linear. At some point when the bearings get to be
sloppy on the crank, the wear accelerates, and the faster it accelerates,
the faster it accelerates. If you want to play the crankshaft roulette
game, you extend TBO until the bearings start to make metal. Then you pull
the engine down, and if you are lucky, the bearings (the cheap part) took
the hit and left the crank journals intact. If you lose, you grind the
crank UNLESS somebody else played crankshaft roulette before you and the
crank had already been ground to minimums. Now you REALLY have a rough row
to hoe, in that you get to find a replacement crank ... which ain't cheap by
anybody's standards.


As Smokey Yunick said, the more often you rebuild, the cheaper it is.
Going much beyond TBO on an aircraft engine-or beyond what the
consensus says is the usual life on other engines, be they car or
boat-is fool's coinage. Dismantle, clean, mike and magnaflux.

Bret Ludwig wrote:
RST Engineering wrote:
snip

The other side of that coin is that bearing/crankshaft wear tends to become
exponential after a point in time when it departs from linear. That is, for
a long time (extrapolated by the manufacturer to be "TBO") the wear on the
bearings and the crank is linear. At some point when the bearings get to be
sloppy on the crank, the wear accelerates, and the faster it accelerates,
the faster it accelerates. If you want to play the crankshaft roulette
game, you extend TBO until the bearings start to make metal. Then you pull
the engine down, and if you are lucky, the bearings (the cheap part) took
the hit and left the crank journals intact. If you lose, you grind the
crank UNLESS somebody else played crankshaft roulette before you and the
crank had already been ground to minimums. Now you REALLY have a rough row
to hoe, in that you get to find a replacement crank ... which ain't cheap by
anybody's standards.



As Smokey Yunick said, the more often you rebuild, the cheaper it is.
Going much beyond TBO on an aircraft engine-or beyond what the
consensus says is the usual life on other engines, be they car or
boat-is fool's coinage. Dismantle, clean, mike and magnaflux.


Smokey was talking car engines, more specifically race car engines. Do
you rebuild your car engine every 100,000 miles as preventive maintenance?

Matt

On 13 Oct 2005 00:02:59 -0700, "Bret Ludwig"
wrote:

As Smokey Yunick said, the more often you rebuild, the cheaper it is.
Going much beyond TBO on an aircraft engine-or beyond what the
consensus says is the usual life on other engines, be they car or
boat-is fool's coinage. Dismantle, clean, mike and magnaflux.

Cheaper for whom? How is it cheaper to rebuild frequently than to run
an engine for it's normal life?

Was Smokey a pilot? Was this comment directed at aviation engines? Is
it relevant?

Corky Scott

wrote in message
Was Smokey a pilot? Was this comment directed at aviation engines? Is
it relevant?

Smokey was a pilot. Parked a Bell 206 on the property.

D.

Steve Foley wrote:
Yup. It's run out, and will need replacement/rebuilding shortly. Like you
said, anything else is gravy.

Don't you have a T-Craft engine?

"Michael Horowitz" wrote in message
...

I have a lead on a Tcraft with an A-65 engine that has exceeded
recommended TBO. It is my understanding the compression is still good.

How should I approach this engine ( i.e. just assume everything over
1800 hours was a freebee and there is no guarantee it's not about to
poop out)? - Mike




Baloney. Engine life is highly variable depending on usage, care in
maintenance, etc. An engine run infrequently and not maintained well
might not make it to 500 hours. An engine run every day and maintained
well might run to 3,000 hours.


Matt

I have a lead on a Tcraft with an A-65 engine that has exceeded
recommended TBO. It is my understanding the compression is still good.

How should I approach this engine ( i.e. just assume everything over
1800 hours was a freebee and there is no guarantee it's not about to
poop out)? - Mike


A friend of mine at our local AP (3S8) has an Apache (twin O-320's).
After 3500 hours on the engines he decided they needed an overhaul (only
because he wants to give instruction in it).
So the actual number of hours on the engine means little. What really
matters is how it was taken care of / flown...

I'm not sure what you base your assumption that it will NEED
replacement/rebuilding shortly. My old Chief had 2400 hours on its
C-85. Compressions were well into the upper 70s. I have a friend who
flew Citabrias to 10000 hours between overhauls. The key to that long
of a life was useage. They used them for power line patrol and flew
10-12 hours daily. He believed the key to longevity was usage. Sitting
unused it what kills these engines...TBO is RECOMMENDED, unless it is
used in commercial operations, where it's required.

Scott


Steve Foley wrote:
Yup. It's run out, and will need replacement/rebuilding shortly. Like you
said, anything else is gravy.

Don't you have a T-Craft engine?

"Michael Horowitz" wrote in message
...

I have a lead on a Tcraft with an A-65 engine that has exceeded
recommended TBO. It is my understanding the compression is still good.

How should I approach this engine ( i.e. just assume everything over
1800 hours was a freebee and there is no guarantee it's not about to
poop out)? - Mike

The question to which I replied was "How should I approach this engine?"

The question was not "How long will this engine last?". The question was not
"How can I tell how long this engine will last?"

I believe that when purchasing a plane with an engine beyond TBO , expect
the worst. Expect to will need replacement shortly. I never said it WOULD
need replacement. I said to treat it as if it would need replacement, and
pay accordingly.

It appears everyone else thinks you should closely examine the logs to see
if it has been well cared for, and offer more for the plane as a result. I
disagree.


"Scott" wrote in message
...
I'm not sure what you base your assumption that it will NEED
replacement/rebuilding shortly. My old Chief had 2400 hours on its
C-85. Compressions were well into the upper 70s. I have a friend who
flew Citabrias to 10000 hours between overhauls. The key to that long
of a life was useage. They used them for power line patrol and flew
10-12 hours daily. He believed the key to longevity was usage. Sitting
unused it what kills these engines...TBO is RECOMMENDED, unless it is
used in commercial operations, where it's required.

Scott


Steve Foley wrote:
Yup. It's run out, and will need replacement/rebuilding shortly. Like
you
said, anything else is gravy.

Don't you have a T-Craft engine?

"Michael Horowitz" wrote in message
...

I have a lead on a Tcraft with an A-65 engine that has exceeded
recommended TBO. It is my understanding the compression is still good.

How should I approach this engine ( i.e. just assume everything over
1800 hours was a freebee and there is no guarantee it's not about to
poop out)? - Mike

Yes, you DID say it would NEED replacement/rebuilding.

Scott

Steve Foley wrote:
I never said it WOULD
need replacement. I said to treat it as if it would need replacement, and
pay accordingly.

The original message said:

Steve Foley wrote:

Yup. It's run out, and will need replacement/rebuilding shortly.

Again, the question I replied to was:

"How should I approach this engine"

My reply was to that EXACT question, not to some other question you may have
imagined. Implied in my response (because it was a direct response to the
question) was that it should be APPROACHED as if it's run out.

"Scott" wrote in message
...
Yes, you DID say it would NEED replacement/rebuilding.

Scott

Steve Foley wrote:
I never said it WOULD
need replacement. I said to treat it as if it would need replacement,
and
pay accordingly.

The original message said:

Steve Foley wrote:

Yup. It's run out, and will need replacement/rebuilding shortly.