TBO v. # of Years in Engine

Ventucky Red

Ventucky Red

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Jon
General question.... looking at a plane with a Lycoming Engine 0-235 to be exact... the plane has the original engine with 1900 hours, but the plane is a 79.. should this be of a concern? It got through an annual mid last year w/consistent compressions and has not been flown.. nor has the engine opened up... Am I over thinking this or is there some caution to wind here to be concerend about?

All Lycoming Engines have a recommended calendar overhaul of 12 years regardless of the time on the engine. The recommended time to overhaul is important for a couple of reasons: engines that operate infrequently often have a much higher chance of corrosion forming on parts exposed to the environment, and the engine uses composite gaskets and rubber hoses that degrade over time and could affect the reliability of your engine.
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Crap shoot. Our airplane is a 57 172 with a engine rebuild in the early 80s. Actually this engine was put in from another airplane. It has about 1400 hours on a 1800 TBO. We have had it a little over a year and have put a little over 100 hours on it. We put two new cylinders on it the last annual. We bought ours priced right so. If it runs good it runs good if it is priced right fly it until it doesn't.
 
what's the amortized flying usage over the last 36 months? That's my inflection point when it comes to running on condition. Co-worker of mine tried to sell me a mooney he has sat for 24 months (still sitting actually), and admitted to ground running (pending repairs to engine mount and other A/P availability fac built typical nonsense). I gave him the llama meme look. Like come on, at least try that with a neophyte, not someone who you know owns these things too. His hope is exactly what I'd do, fly a bunch of hours to put the period of sitting in the logs behind him, and be able to market/sell it to the next sucker (not an indictment on any one individual, we're all relative suckers in this game of overprized tractor engine hot potato) to deal with.

BL, if that cam has had the opportunity to dry up, the chances of spalling on the Lyco side go up, and at that point you're gambling with cracking it open well before you bargained for. If it has flown circa 40 hours a year or better with no periods of 12-month sitting in between, no guarantee, but at least I would feel more inclined to pull the trigger. To each their own of course.

Other than that, you're pricing it as needing an OH for continued airworthiness, and my experience is most sellers punt at that pricing offer. The thing just gets parted out or sold to someone who doesn't know any better. Good luck to ya.
 
Ventucky Red said:
General question.... looking at a plane with a Lycoming Engine 0-235 to be exact... the plane has the original engine with 1900 hours, but the plane is a 79.. should this be of a concern? It got through an annual mid last year w/consistent compressions and has not been flown.. nor has the engine opened up... Am I over thinking this or is there some caution to wind here to be concerend about?
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Lycomings are not engines you want sitting for long periods without being run.

DFH65 said:
Crap shoot. Our airplane is a 57 172 with a engine rebuild in the early 80s. Actually this engine was put in from another airplane. It has about 1400 hours on a 1800 TBO. We have had it a little over a year and have put a little over 100 hours on it. We put two new cylinders on it the last annual. We bought ours priced right so. If it runs good it runs good if it is priced right fly it until it doesn't.
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Continental engine, different animal.
 
Total gamble to be honest. Compressions don't mean much if it's because the pits are full of rust. It's a run out engine plain and simple. Do a price comparison on ones with low time engines and adjust accordingly.
 
Both Lycs and Continentals suffer corrosion. Lyc's cam is in the top of the case instead of under the crank, and a sump heater can drive moisture out of the oil and the vapor rises up and condenses on that cold camshaft first. But neither engine cares for being ground-run and put away. That's a really good way to kill it. Fly it or leave it alone.

An engine is much more than its camshaft. It has steel cylinders with aluminum pistons in them, so galvanic corrosion happens if any moisture is left in there. There are steel gears in the accessory case that rust. Galvanic corrosion happens between the bearing shells and crank bearing surfaces. Magnetos suffer with age, and not just corrosion; grease dries out in the bearings and on the rubbing block, coil insulation shrinks and cracks, seals harden and crumble. Plastic and rubber fuel system parts shrink or swell and harden or soften and leak. Hoses go hard, usually, and can crumble internally and plug stuff up or just fail and blow oil or fuel everywhere. Valve stems corrode, valve faces and seats corrode.
 
Look at the logs and hours between dates. Look for long periods of inactivity.

Use a borescope to get a visual on cylinder wall corrosion as a litmus test for the rest of the condition.

Then discount it accordingly, using a premium for your risk, if you’re still willing to take a chance.
 
The engine hours are damn near run out regardless. So it'll need an overhaul relatively soon either way. How many planes really fly 150 plus hours a year? Most GA planes probably see less than 50 a year. Are most getting rebuilt at 600 hours? I'm sure some are, but a vast majority are not. They may not hit the 2000 HR threshold, but I doubt anyone really pays attention to calendar hours.
 
TBO is advisory for non-commercial operators. Lycoming puts a 12 year TSO limit on things regardless of hours. If you've got a constant speed prop, the prop itself might only have 5 years on the TBO.
As Racers points out, planes that aren't flown frequently rarely make it anywhere near TSO. Those who are flown and maintained a lot can sail through the TBO hour limits. I was flying a 172 with 2500+ past the last major and it was still going strong. The owner finally overhauled because he got tired of the club president griping about it.
 
Most of the O-235s have a 2400 hour TBO. But the O-235 is also famous for running cool, which means considerable moisture accumulating in the case on short flights or ground runs. We had one in a Citabria that would start making metal at around mid-time on both engines that it had when I was there. Moisture, especially in colder weather, would accumulate and start galvanic corrosion happening on the cylinder walls. After they pitted enough, the rings would wear the cylinder rapidly enough to leave a ridge at the bottom of the ring travels, and that ridge would start shaving aluminum chips off the piston pin plugs. The chips showed up in the filter screen. The cylinders would come off when the debris became significant and we'd find water droplets on the piston skirts and cylinder walls and in the rocker boxes, all from the runup just before draining the oil for the 50- or 100-hour inspection. The cylinders got honed and measured to see that they were still within service limits, and new pin plugs installed. We put the winter plate on the oil cooler and left it there year-round, trying to get the oil temp up.

Most O-235s are also famous for hard starting, so many have two impulse mags. You have to watch those impulse springs for corrosion, too. A busted impulse spring means the mag timing goes pretty much to TDC. No power from that mag. No power at all if they both manage to break.
 
I order to know what "RUN OUT" means you must know what TBO is and the understand the terms..

every one ?
 
Ten years ago I met a sad looking airplane.

It had not flown in 23 years.

The PA28 was up on tall jacks so that when; not if, the Alleghany River would flood.

One mag was off also.

We pulled all jugs and found found the Cam was fine.

Eventually the aircraft was returned to service.

In about 6 years and 300 hours the Engine has been fine.


Note with the O-235 engines that the Lifters are not hydraulic.

Checking adjustment every 100 hrs will give you warning of Cam issues.

It’s a high time engine; if priced accordingly go for it.
 
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I bought a ‘65 O-360 with 2300 hours on it and no bottom overhaul since birth and ran it to almost 2700 before I decided to tear it down. It worked out fine for me. Though, the overhaul was pricier than your average since every AD had to be done, pretty much everything forward of the firewall needed overhaul or replacement. Upside is now I know everything has been dealt with properly.
 
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