High time or Low time and time in storage.

[c170b53]

There’s often inquires on the merits of purchasing a plane with either a high time engine or a low time engine. Possibly the time in service and the conditions are just as or more important. A fellow member had a stuck valve issue in flight and was motivated to investigate beyond just doing the rope trick/ream. The engine had 100 hours since overhaul. The engine was low time but it had sat idle in storage for 10 years prior to being acquired by the member. The engine had been put into service with no problems until the stuck valve issue surfaced 100 hours later. Two valve springs were subsequently found broken on different cylinders which motivated further investigation. Upon pulling a cylinder the piston rings were found seized in the piston so the owner elected to pull all the cylinders. The cylinders ( ECI’s) were honed, valves lapped and the guides cleaned. New pistons and rings were fitted and the engine was reassembled.
Run-up was normal as was the 40 min flight test although it was thought the oil temp was a bit high (Likely piston ring break-in), Several days later the airplane was taken out for a burger run but 20 min after lift off the engine began to shake. A 180 turn was executed and a successful landing was carried out. On the ground number 2 cylinder had the appearance of having overheated. A subsequent compression check found number 2 with no compression.
This afternoon the owner and 3 helpers (all mechanics (including me) hangared the airplane to remove number 2. We all worked simultaneously and during this process I went to remove the H/T lead for the lower plug. I put the 3/4 wrench on the lead and I found the plug turned a bit, so I just held the H/T lead lug while undoing the nut on the plug (the right way to do it) and remarked the spark plug must be a bit loose. I didn’t think much of it but my remark started a discussion of spark plug torques, angles of plugs and annealing of washers. We carried on. About 40 mins later the cylinder came off and I guess it wasn’t that hard to see the problem. As a matter of fact if I had bent down and looked at what I was doing rather than just feeling around with my fingers, I would have spoiled the find earlier.
Here it is

31AA9A80-EF5A-4588-BCBF-29117409A915.jpeg

and here again with the plug out.

[c170b53]

So this is a 200 hour smoh but 12 years in service. Note on a historical basis we went from on-condition then added time then added cycles then calendar time to qualify airworthiness in commercial aviation. Not to say that’s required but maybe all the stats should be considered. when evaluating a purchase..

[GAHorn]

JIm, by chance, was that a cylinder which had a spark plug bushing installed?

[c170b53]

No bushing just normal steel insert thread for the plug. I should have taken a pic of the cylinder head from the barrel side. Inside, the area cracked out is a bit larger than the outside area. I didn’t look at it long but there almost looked like a crack starting at the intake valve seat across to the spark plug area. I’ll get a pic next week if I can and post.