eddsPeter wrote:
So we did know buying a hangar queen and therefor we took really care on the maintenance especially regarding the engine.
If you don’t mind sharing, what exactly was done? Were any cylinders pulled? Or did you have a top overhaul, and if so, how long ago in terms of hours?
First the engine was boroscoped and the lifters where changed. Then about 500 hours later we had a top overhaul with all cylinders pulled and the lifters changed again. 100 hours later again the lifters made some trouble and where changed on guarantee.
Now about 300 hours ago one cylinder was pulled. Then about 100 hours ago the propeller governor was overhauled and 20 hours ago the starter was overhauled.
We bought the bonanza with about 175 hours on the engine flown in 11 years. Now the engine had about 1505 hours.
eddsPeter wrote:
We bought the bonanza with about 175 hours on the engine flown in 11 years. Now the engine had about 1505 hours.
But if you make it from 175 to 1505 hours, do you still speculate that the limited use from 0 to 175 had a lasting impact on the engine?
mmgreve wrote:
But if you make it from 175 to 1505 hours, do you still speculate that the limited use from 0 to 175 had a lasting impact on the engine?
The worst damage from disuse seems to be cylinder wall corrosion (and camshafts/lifters on Lycomings but this is a Conti). That damage will stay with the engine but as Peter writes he put in new cylinders that damage was most likely no longer present.
I don’t think this stuff (corrosion / pitting / spalling) ever causes a sudden total failure. This sounds like a conrod broke or, if there were earlier signs, perhaps a piston seized up, or a valve broke and smashed up a piston and then other things broke, etc. Or even the crankshaft broke.
@Antonio wrote:
Hi Frans! Would you be able to share some more data on the referred accident that we can learn from?Hi Antonio! Yes, I will write an separate topic on that incident later on. I will meet him on upcoming Friday, so I hope to bring some useful information afterwards.
I guess @eddsPeter will have the parts examined to check which of them has caused the catastrophic failure.
Concerning corrosion, I have bad news:
When we had our engine – Conti IO 520 BB – in overhaul this year (due to large metal chips in the oil), it turned out there was corrosion on the crankshaft. There’s been a phase we know the oil replacement cycles were to long, essentially 100hrs. I know this is insane and I don’t want to elaborate as to why it happened.
To cut a long story short: Anything that can cause corrosion can also cause corrosion on the crankshaft, which cannot be seen with any inspection other than disassembling. And once the hardened surface alloy has been damaged by corrosion (as in our case), these damages go deeper and deeper, and the crankshaft looses strength over time, which can (!) eventually lead to a catastrophic, sudden death of the engine. This is just to remind everyone that a) not changing the oil often enough, b) engine inoperative for longer periods, or c) operating the engine in generally salty and / or humid climate can cause ‘unknown unknown’ damages.
After the stuff I wen through this year with our Conti I won’t ever buy a hangar queen.
Very sorry to hear of yet another engine story, @EuroFlyer.
2019 has clearly been the “year of the engine”. Not all I know of have been revealed, either…
I would be amazed that running oil to 100hrs will alone cause corrosion. OK; it will look like the stuff they make roads with. But why should it corrode?
What is known is that it takes a while, at full engine operating temperature, to boil off the water in the oil. So a long succession of short flights – say under 30 mins – is a risk. But that’s with any oil, even if 10hrs old. Obviously, completely fresh oil won’t have water in it.
Where did you find metal? Oil filter, or the strainer (not sure if Contis have the strainer)? Which parts did the metal come from?
The large metal chips originally must have come from one or two faulty lifters, ending up in the oil filter where they were found.
Before ending up there, they had travelled through the engine with the oil, carving deep grooves in the oil pump housing, the camshaft gear and associated cogwheels, and some other parts; some of them even ended up in the starter coil. The engine was considered not airworthy, brought to a large engine shop, where it was dissassembled. Only then the crankshaft corrosion damage came to light. We had to replace the crankshaft which is the most expensive part of the whole engine.
Essentially, as far as I understand what happens, is that acidic and aggressive residuals from combustion form some kind of oil-acid slime over time, which eventually eats itself through the harding alloy, preferrably if there are any pre-existing grooves or microscopic damages. The damage was on the shaft sitting inside the bearing, a large stain where the entire alloy was gone. Not visible from the outside. It had to be taken out completely to see it.
Acidic products of combustion in the oil apparently cause corrosion. Whether crankshaft corrosion pitting often leads to fatigue cracking and crankshaft failure is another issue. It is certainly possible, but the possibility does not automatically make it a probability. There have been ADs focused on specific areas on specific crankshafts.
Inspecting the oil filter for metal at each filter change is a very good idea.
