Engine teardown vs overhaul?

FredFenster

FredFenster

Pre-takeoff checklist
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Greg L
Is an engine overhaul significantly more expensive or involved than a teardown inspection after a prop strike? I'm seeing ads for airplanes that have had prop strikes and they're listing the engine times for example 1000 SMOH, 200 Since teardown for prop strike. If you're pulling the engine that far apart which I'm guessing isn't cheap in the first place, why wouldn't you just completely overhaul it at that point and put the prop strike in the past?
 
FredFenster said:
Is an engine overhaul significantly more expensive or involved than a teardown inspection after a prop strike? I'm seeing ads for airplanes that have had prop strikes and they're listing the engine times for example 1000 SMOH, 200 Since teardown for prop strike. If you're pulling the engine that far apart which I'm guessing isn't cheap in the first place, why wouldn't you just completely overhaul it at that point and put the prop strike in the past?
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The parts to overhaul aren't cheap and my guess is that's all the insurance company wants to pay for.
 
The answer, as with all things is it depends. If you just take off two jugs on one side, split the case, and inspect the crank for cracks, then button it back up with new rod bolts and nuts, and a gasket set, that's not much cost. Compared to a factory reman, or a field OH to new limits, the cost delta is significant.

The other way is a complete engine disassembly, magniflux and x-ray the crank, rods, rod caps, all acc gears, and inspect and replace any parts not found in service limits, to a field OH within service limits, the price delta won't be that high.

If I had a good running engine with ~200 hours, I would just do the teardown insp, and maybe new rings and a hone job depending on comp at the time. If I had an engine >1000 hours, I'd prolly just do a new limits field OH.
 
docmirror said:
The answer, as with all things is it depends. If you just take off two jugs on one side, split the case, and inspect the crank for cracks, then button it back up with new rod bolts and nuts, and a gasket set, that's not much cost.
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Aha, didn't know that was an option. I assumed teardown meant the crank had to come out, didn't know you could just pull it half apart and inspect it.
 
FredFenster said:
Aha, didn't know that was an option. I assumed teardown meant the crank had to come out, didn't know you could just pull it half apart and inspect it.
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Well, the inspection depends again on what the mfg says it must include. There are likely some engine cranks that need to be removed and magged, or some other expensive option. I think the FAA worded the requirement very broad and left it up to the engine maker to decide what specific "inspection" actions need to be performed.
 
A typical propstrike inspection needs more than a visual check. You can't possibly see the tiny cracks that might have started, especially in the bearing surface fillets. The crank, rods, case, gears and so on need NDI. I had a crank break in flight, from an ancient propstrike, and the crack would never have been caught visually right after the event. I've had cranks come back after propstrike inspections (when in flight school aircraft maintenance) and the cracks the NDI found were extremely hard to see, even after the NDI guy had circled them.

Dan
 
Having just gone down the road in the last year I can tell you that the prop strike inspection on a Continental o-470 was 10K while a rebuilt was 22K. My partnership decided on the rebuild as we had ~1500 hours out of a 2000 TBO.
 
jtheune said:
Having just gone down the road in the last year I can tell you that the prop strike inspection on a Continental o-470 was 10K while a rebuilt was 22K. My partnership decided on the rebuild as we had ~1500 hours out of a 2000 TBO.
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O-470s have 2000hr TBO? :confused:

Hmm.. Just looked the O-470U has 2000/2200 hr TBO.
 
I was going to say, as confirmed above, that labor is definitely under half the cost of an overhaul. So the answer to the question "why wouldn't you just..." is because it costs twice as much. Of course it also depends on the time and condition of the engine as it is. If it's close to needing an overhaul then obviously that changes things but then there is the BIG bottom line of what is the insurance going to pay for? They are going to pay for the required tear down and inspection, they aren't going to pay for the replacement of worn out parts unrelated to the prop strike.
 
A proper propstrike inspection should involve tearing the bottom end down completely and NDTing everything.
Here are some of the things that can be found;

Cases can crack in the bearing saddles/webs

Counterweights can crack at the bushing holes - not a pretty failure later

Any of the gears can crack a tooth, or crack at the bolt or dowel holes

Lycoming cranks will usually bend at the flange, but even if they 'dial out OK' they can crack at the prop bushing holes as well as crank webs

Continental cranks don't bend, but they can nearly shatter in the seal/front main bearing area without being measurably off. - Our favorite NDT demo piece is an IO-550 crank with no runout, no visible damage and multiple cracks running more than 180 degrees just behind the flange. In no way detectable without magnetic inspection.

Cont. front alternator engines can crack at the alternator drive gear - either the gear itself, or the crank where it bolts down. Again, not a pretty failure later.




A full overhaul will involve new (or overhauled) cylinders, magnetos, fuel systems and a potential horde of mandatory replacement parts per the manufacturer's recommendation.

A good way to figure out what is the better economic choice is to figure a cost of hourly operation.
Overhaul cost divided by TBO = X
Propstrike Inspection cost divided by time remaining until TBO =Y

if Y is greater than X, then overhaul is a better option.
 
FredFenster said:
Is an engine overhaul significantly more expensive or involved than a teardown inspection after a prop strike? I'm seeing ads for airplanes that have had prop strikes and they're listing the engine times for example 1000 SMOH, 200 Since teardown for prop strike. If you're pulling the engine that far apart which I'm guessing isn't cheap in the first place, why wouldn't you just completely overhaul it at that point and put the prop strike in the past?
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The tear downs and inspections on my engines were going to be $7500 each including R&R.
 
AESpecialists said:
Continental cranks don't bend, but they can nearly shatter in the seal/front main bearing area without being measurably off. - Our favorite NDT demo piece is an IO-550 crank with no runout, no visible damage and multiple cracks running more than 180 degrees just behind the flange. In no way detectable without magnetic inspection.

Cont. front alternator engines can crack at the alternator drive gear - either the gear itself, or the crank where it bolts down. Again, not a pretty failure later.
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Can you post any pictures? I'd love to see that :yes:
 
Henning said:
The tear downs and inspections on my engines were going to be $7500 each including R&R.
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What kind of fire are you playing with just sending them for exchange? How much can you lose on core charges?

I see many core well north of $10k these days
 
bnt83 said:
What kind of fire are you playing with just sending them for exchange? How much can you lose on core charges?

I see many core well north of $10k these days
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No clue, they totaled my plane, I just saw that was the quote the insurance got.
 
AESpecialists said:
Love too, but I'm not seeing a way to directly upload the picture without using a third party gallery
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If you Reply to this, you will see a paperclip above, from there you can directly attach files in a two step process, first attach it into the dialogue box, then tap the paper clip a second time and select the file you want to attach.
 
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