On May 24, 3:38 pm, "Robert M. Gary" wrote:
On May 24, 4:03 am, wrote:

On 23 May 2007 08:09:20 -0700, "Robert M. Gary"
wrote:
Please bear in mind that one of the two piston pin plugs on each
piston pin is going to be in contact with the cylinder wall during
normal operations.

The lab analysis is relative. They show my AL vs. other IO-360's and
mine has been 2-10 times higher than all others for the last 3 years.

Again, the piston pin plug is a relatively soft alloy, it may transfer
to the cylinder wall like a crayon, but it is not going to disturb the
material of the cylinder wall.

The pins wear when the rings leave a ridge in the cylinder
wall at the bottom of their travel. In engines that do not have rings
beneath the pison pin as well as above it, the pin plugs ride over the
ridge and get shaved, creating those aluminum hairs you see in the
filter. If an engine has rings below the pin, the ridge will be below
the pin plug's travel and it won't get shaved.
The ridge will form much quicker on engines that run too cold
or get flown too little. The blowby gases contain water vapour, which
condenses in the case and can also form on cooler parts of the
cylinder walls, such as those exposed to the incoming cooling air.
Corrosion forms wherever moisture collects, and a corroded cylinder
wall will wear at an astonishing rate and will form a ridge more
quickly. So now we have aluminum AND iron in the oil analysis.
We've had this trouble with an O-235 that just runs way too
cold, even in summer. The oil temp seldom gets far of the peg, and in
the winter it won't warm up much at all, even with the cooler blocked
off. I was able to isolate the bad cylinder with a sharpened piece of
welding rod, feeling the cylinder walls and finding the roughness, but
ended up taking them all off anyway. The danger with an ignored
failing pin plug is that it can end up rattling around in there and
jamming things, or leave altogether and rip up the piston or let the
pin end take the cylinder wall apart.
Bronze pins are available for some engines. They're more
resistant to the shaving, but the engine still has to come apart and
the cylinders fixed up. It's false economy to let it go.

Dan