I think the plug is aluminium. The small end pin is of course steel.
I will ask the engine shop.
Peter wrote:
the plug is aluminium
So do I. At least on engines I worked on, all were aluminum. But I’ve seen some made out of brass as well.
As for the pin working directly against the cylinder wall, that would be a totally worn plug. Or one, or both, plugs not installed when the cylinder was installed.
Thanks for reminder about aluminum piston pin plugs in Lycomings, I’d forgotten. I’ve spent a lot more time working on engines with snap rings or circlips and no plugs.
I am told my plugs were brass.
I dodged an expensive Lyco AD by the engine shop using Superior parts.
2nd aluminium spike, after a sample with no aluminium elevation
However, borescope images show a chunk of crap having come off the piston crown right at that spot so that may be it
A belated explanation: Lycoming had three different designs of piston pin plugs, made of two different materials:
For details, see SI 1267D.
Interesting that all 3 above contain aluminium.
There was also the Superior replacement.
However, it seems clear that the dome surface of the plug cannot possibly produce a nice even wide scrape on the cylinder wall. The culprit is probably a piece of deposit which came off.
