When mine was opened after 800hrs (for the SB569 crank swap ) only the six exhaust valves were found to be outside new limits. The cam followers also showed signs of spalling (surface damage) which is normal, and they were replaced too.
It makes me wonder what really does wear provided you look after the engine…
To me it seems these engines would make TBO a number of times over, provided they didn’t get bunged up with rubbish which stops the bottom piston rings sealing off the oil.
Cylinder barrels become oval, rings lose material and don’t seal well anymore. Bearings start to leak. Dirt/sludge accumulates. Valves burn and eventually crack.
Engines do have life limits, there is constant wear everywhere, whether it’s car, boat or airplane. I’ve taken about a dozen engines apart in the last year and the wear patterns are all very similar.
The wear is more a product of the number of cold starts rather than hours run. They say a cold start in sub zero temperature is the same as 1000 km of operation, which should be about 10 hours run or something. The longer trips you have, the longer the engine will last.
If this is somewhat true, then:
Peter wrote:
. The cam followers also showed signs of spalling (surface damage) which is normal,
At 800 hrs your cam was spalling? Lifters what did they look like?
Sitting unused, is what wears them. If they’re run daily, many hours they’ll make well above TBO.
LeSving wrote:
100 1 hour flight = 10*100 + 100 = 1100 “wear hours”
Wouldn’t that bankrupt every single flying school?
AdamFrisch wrote:
Sitting unused, is what wears them. If they’re run daily, many hours they’ll make well above TBO.
One keeps hearing that but I still think it is largely untrue. Apart from cases where the climate makes the metal rust very fast, it is not what I observe and also not in line with my experience with various engines. The wear from engine runtime by far outweighs the wear from sitting unused. Our boat engines run between 2000 and 4000h a year and there is an almost direct correlation between engine wear and hours on the engine.
NIL: Crankcases wear out and crack. The IO-360 that I posted here with the cracked crankcase was also found to be fretting and needs oversize through-bolts to correct. That’s 3500h T TIS, 1500h SMOH.
I have to imagine (well, hope really) that in terms of startups, the startup that causes the wear is the first start of the day, particularly if it’s cold. Subsequent starts with the engine still warm and every surface still slathered in oil probably do just a fraction of the wear. (When aerotowing gliders, I might do a dozen 10 minute flights in an afternoon, this is why I hope this is true :-))
Corrosion due to lack of use expasipated by low oil operating temp and cold starts are the biggest causes of engine deterioration.
