Post Thu Apr 12, 2012 6:36 am

Repro piston groove problem

I found a problem on a new piston. I do not know the brand but it has a sign cast in, on the inside. It is a circle with a horizontal line inside and a somewhat larger circle around it not, centred but tangentially touching, making what looks like a partial solar eclipse or a 3/4 dark moon. Anyone who knows this brand?
The oil control ring has an expander. When I tried to push this ring in the groove, it required tremendous force. Definitely not good. It looked like the groove was possibly not deep enough. I then compared things with a 40 year old Bohnalite piston, put on NOS HD rings and found that things looked fine. Measured the groove depth and found that it was 1 mm (.04") deeper in the old piston which explained everything. (Rings and expander were the same design on both pistons.) Has anyone seen this type of problem before?