Reply To: Piston rings for MK25

[Dale]

Charles a general rule of thumb is .004 for every inch of bore, so 3inch bore about 10 to 12 thou.  The biggest thing to watch is they need some end gap.   Mercury rings that I have bought were about 2 thou and that is asking for trouble.  I clamp a point file in the vice and squeeze the ends of the rings on the file.  It doesn’t take long to open them up some.   Elmer K did not want the back yard mechanic to have important information about his motors.  Hope this helps

dale