O-360 UOA and Break-in

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In Feb 2018 I installed a Penn Yan O-360 overhauled to new limits, in my C-172. Effectively, a new engine. I ran the normal recommended break-in procedures (high power, rich with shallow climbs to keep it cool). Oil consumption stabilized at about 1 qt per 15 hours, within the first 10 hours but I continued the break-in for the recommended 50 hours. After that I switched to Philips 20w50 AD.

Did the first UOA at the 5th oil change at 147 hours total (46 hours on oil). Everything normal except Aluminum (17/6), Chrome (33/8) and Copper (13/3) were elevated. Numbers are ppm in UOA versus averages. Blackstone says this looks high, they expect metals back to normal levels by now.

Oil filters and screen have been clean. Compressions are excellent (80/80 all around), borescope looked excellent. No obvious problems.

Next UOA at 42 hours later. Everything normal, but for the same 3 elements. Numbers below are: this UOA, prior UOA, averages for this engine:
Aluminum: 13, 17, 6
Chrome: 18, 33, 8
Copper: 10, 13, 3

I asked Blackstone and they said: Glad to hear that the engine is checking out on your end. The metals are heading in the right direction. Couple that with the good compressions and borescope results and I'd be really surprised if there's a problem developing. Best course of action is to probably just see how things look next time.

My prior engine failed (corroded cam lobes) without anything bad showing over 8 years of UOAs. So I had a bad engine with good UOA. Now it looks like I have the opposite: a good engine with bad UOAs. This is making UOA look pretty useless, with both a false negative, and now false positives.

I'm inclined to stop doing UOAs at all. Just inspect the filter and screen and maintain the engine on actual condition. Convince me otherwise; tell me why I shouldn't.
 
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Subscribed. You're not the first member to report having good UOA reports and an engine failure, or lousy reports and a good running long lasting engine.
 
Given that you are still only have H, the numbers are trending down, borescope and compression are good, I would not worry too much. I would keep doing oil samples though, they can highlight issues. For us it was a wearing wrist pin.


We are at ~300 hours on our O-540's Penn Yan overhaul. Great engine.

Happy flying!
 
Originally Posted by wings&wheels
... I would keep doing oil samples though, they can highlight issues. ...

Yes, UOA can highlight issues. But they don't always detect issues. And conversely, they can give you false warnings. So:
If the UOA is good, your engine isn't necessarily sound.
If the UOA is bad, your engine doesn't necessarily have a problem.

Put differently: Most tests are either high precision or high recall.

High precision means it doesn't say there's a problem unless there is overwhelming evidence. It won't always detect a problem, but when it does, you can be sure that it's a real problem. It may have false negatives, but not false positives. Sometimes called high specificity.

High recall means it has a hair-trigger response. it always detects a real problem, though it also throws out false alarms. It may have false positives, but not false negatives. Sometimes called high sensitivity.

Either of these kinds of tests are useful, for different reasons. But UOA is neither of these. I've seen it give both false positives & false negatives, which makes it much less reliable or useful than either of the above.
 
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