Avidflyer2
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Background Info - Piper Cherokee PA28-140 Lycoming O-320 Engine (160HP) at or near TBO. Last oil change 30 hours ago without any signs of metal in oil filter. Airplane was being flown on a cross country flight of more than 4 hours when it started to lose oil pressure in flight without a increase in oil temperature. An uneventful landing was made at the nearest airport to investigate. Engine oil level at 5 qts, after a suitable cooling down period the engine was run up again and found having normal oil pressure / temps. Another takeoff was made with the airplane staying in the traffic pattern, within 20 minutes oil pressure started dropping with no apparent increase in oil temp. Pilot/Owner had stated that in the previous 10 hours the oil consumption had increased from .2 qt/hr to 1 qt/hr. A local mechanic pulled the engine oil filter cartridge and found substantial aluminum particles in the filter element. An engine swap was made to recover the airplane to its home base.
I have had spigoted piston pin end cap failures before, but not to this extent. Usually a small amount of aluminum is found in the filter and a borescope inspection of the cylinders may or may not reveal which is the offending cylinder. Both Lycoming and Continental have had difficulties with their piston pins. I have not been able to find out exactly WHY the end caps wear. In this example it is pretty obvious that the spigot broke off at the end of the piston pin and flailed about in the piston's wrist pin bore. I don't like the spigoted pins because they tend to accumulate carbon or other deposits in the piston p[n bore thus making it difficult to remove the piston pin from the piston and connecting rod small end. Its difficult to clean out the bore with the piston pin installed, sometimes the pin has to be pressed out over the carbon deposits - even if that means removing the connecting rod from the crankshaft to avoid damaging the connecting rod. The original piston pin end caps do a better job of keeping the piston pin bore clean with only a small carbon ring between the connecting rod and piston.
Any ideas exactly why there may be any type of side loading on the piston pins to cause them to wear against the cylinder walls?
