Piston failure

[HawgRyder]

Walt...the buttons are installed at a 90deg angle to the wrist pin...in the lower skirt.
Depending on the type of engine...and the amount of "exposure" of the skirt at its lowest point...the buttons can be far down the skirt.
The furthest down the better (from a geometric point of view) and we used to overbore the holes and use the next size ring for sealing (giving even less friction).
The buttons in the wrist pin holes are nice...you can force fit them slightly...and the result is a very "tight" feel to the engine.
We found a particular type of Teflon (happened to be red in colour) wa sthe best.
Almost no wear we could see after several thound miles of use...and re-usable in most cases.
The secret is the shape of the buttons...the head of the button is slightly crowned (end that touches the cylinder wall) and the stem (think mushroom) is inserted into the recessed hole drilled in the piston.
The stem is a force fit so it does not pop out during installation (we made them with a little bulge on the end so it popped into place).
And the hole in the piston was square counter sunk so the diameter of the button was supported.
In most cases..we used either 3 or 4 buttons on each side so that the piston hed no "rock" at all.
We even used them on some snow-mobile engines...2 strokes..but had to be careful the buttons did not get into the ports in the cylinder walls.
I wish I still had some pics of these things...but too many moves have lost them.
Bob