School me on TBO

[Bell206]

Should I only plan on getting another 200-400 hours before needing a Major, or should the TO drag that out?

There's no real answer to that unless you are required to follow the OEM recommendations. Technically there is only one overhaul time period for the whole engine which is currently at 1600. In reality "Top OH" is nothing more than a marketing term. And whether repairing/replacing the cylinders breathes new life into a 1600 hour lower end... who knows for sure. But you'll get plenty of opinions on it.

 

[schmookeeg]

Value the "Top OH" at zero.

Price it according to the 1600 SMOH

...Given that it's a ridiculous seller's market right now, I think this means, practically speaking, to throw elbows, skip prebuys, and add zeroes to purchase prices. Run at the seller with a bag of cash money and throw it all over the place like Rip Taylor because omg you need this plane and everyone else bidding is a tire-kicker.

 

[Capt. Geoffrey Thorpe]

I know I'm dredging up an old thread, but this seemed to be the most pertinent. I'm looking at an Arrow with a Lycoming IO-360 that has 1600 SMOH, but only 135 STOH/SPOH. Should I only plan on getting another 200-400 hours before needing a Major, or should the TO drag that out?

First understand what TBO means: The FAA requires them to publish a number, so they put an engine on a dyno. Run it some. Do a lot of arm waving, roll some knuckle bones, and come up with a number.

In real life, any particular engine can fail due to wear, corrosion, fatigue, abuse, or a defect. The symptoms of failure can be anything between a gaping hole in the block with a rod sticking out to low oil pressure, to "I just don't trust the SOB any more". The time of failure can be anytime between when you buy it to long after you sell it.

What you need to plan on is to plan to deal with whatever happens when it happens.

“Therefore keep watch, because you do not know the day or the hour." Matthew 25:13

 

[Checkout_my_Six]

14cfr33 endurance testing…..run on a test stand for 150 hrs. It’s torn down inspected and some hand waving and wala a TBO number is determined from a sample size of one.

it really in not significant and near meaningless.

 

[Bathman]

A big factor with buying an aircraft with a high houred engine is which engine is installed on the aircraft?

If its a Rotax with 2000 on hours on it. Regardless if its been flown regularly then it’s good for another 2000 plus hours. No question.

If its a Lycoming IO-360-L2A then again there is a good chance it will run many hours over TBO

However if its a O-320-H2AD then its probably not going to.

 

[Magman]

Have to disagree on the H.

They did have early issues and I’m no fan of D mags.

However; a flight school had a H powered 172 that was also used for Banner

Towing.

It was pulled after 3000 hrs with no cylinders off.

Sat around for about a year and then went in a Glastar.

After flying it for a few years the owner then flew NY to Alaska and back.

Flew a few more years and the owner majored it after Lycoming School.

YMMV

 

[Jdm]

Most infrequently flown personal aircraft will not make TBO hours (note that there's also a year, 12 for Lycomings, limit).

Everyone seems to forget about the years when they talk TBO. It’s common for a TBO to have a specified number of years, and hours, whichever comes first.
I’ve had some interesting prebuys because of this.
I inform the buyer that the engine is past TBO because it has 26 years since OH. The seller flips out and calls BS because it only has 700 hrs. I show them the manufacturers website stating the TBO specifications. The seller calls BS again stating that no one cares about that. Try running the appraisal with an an engine out of TBO and see if it makes a difference. Seller says it doesn’t matter bc you can fly it anyway. Of course you can fly it outside of TBO!
Now run the appraisal accurately (with the engine being past TBO) and see if makes a difference!

Gives me a headache!!!

 

[bbchien]

If oil and compression all look good, you can probably go 10% over TBO on a lycoming

 

[Magman]

I’ve had a few folks install new cylinders when nearing TBO.

New Rod Bearings also.

Good opportunity to check Cam.

It’s about as far as you can go w/o splitting the Case.

 

[Jim K]

I know I'm dredging up an old thread, but this seemed to be the most pertinent. I'm looking at an Arrow with a Lycoming IO-360 that has 1600 SMOH, but only 135 STOH/SPOH. Should I only plan on getting another 200-400 hours before needing a Major, or should the TO drag that out?

You do a major because the case needs split, which means crank, main bearings, cam, or something weird like a crack or major leak. The bottom end, if cared for, should be good for 2x tbo or more, especially on an o-360. Cam corrosion from sitting is what usually gets lycos. If you had some assurance the cam was is good shape when they had cylinders off, I would expect it to go another 1000 easily.

That said, have a plan because the crank could split in half tomorrow. As far as valuing it, I'd price it like a 1600 hour engine. The top did add life to it, assuming it was done correctly, and not as a bandaid to fix low compression on an abused or neglected engine.

How comfortable you and your IA are with an engine over TBO is a big part of it. The club I'm in changes engines at tbo+10%, as they're scared of the liability of pushing them any farther. I'm of the belief that an owner should go as long as he's comfortable and the engine isn't "talking to him".

If you haven't found this, it's worth watching (at 1.5x speed):

Opinions vary on Mike, but I think he gets more right than wrong. TBO is his favorite axe to grind and he's written/ said a lot on the subject.

 

[Jeff767]

Most heavily used rentals or working planes like Bell's will sail through TBO without problem. Most infrequently flown personal aircraft will not make TBO hours (note that there's also a year, 12 for Lycomings, limit). Our club 172 was pushing 3000 hours since its second overhaul when the owner finally relented to people's complaints and had it done. It was still going strong.

As pointed out, TBO is advisory for part 91, usually. Unless there's an AD or TC limit specifically indicated.

The above is the key to engine life. A regularly flown aircraft will almost always have a far longer hour time between overhauls. If purchasing a aircraft I would be much happier buying one with 1500 hours that was regularly flown than one with 800 hours that sat for long periods of time.

 

[Jim K]

Our club 172 was pushing 3000 hours since its second overhaul when the owner finally relented to people's complaints and had it done. It was still going strong.

And I'm betting when they opened it up there was nothing at all wrong with the bottom end.

Is it still a bottom end when it's in the middle? Or on top like the Germans did?

 

[Checkout_my_Six]

Here’s one that’s almost 20 years old since overhaul. Lol.

 

[Domenick]

If oil and compression all look good, you can probably go 10% over TBO on a lycoming

You can go a lot longer then that if flown often. It's not unheard of for flight schools to run O-320/360s to 4,000 hours.

I've got an O-320 that is like 700 past TBO and one that is like 300 hours (probably 2 years old). You can't tell the difference between them if you're in the pilot's seat. Actually almost everyone likes the one 700 past TBO more.

I flew an O-320 to 2925 hours in a Warrior. That's almost 50% over TBO. At the time I replaced it, it was still making book static RPM, though there were other issues which had made me loose confidence in it, and I was hesitant to take it over the Cascade Mountains.