[A Broken 417 Piston; Click to See a Larger Image]

A Broken Piston

The number 3 piston broke at approximately 60,000 miles after the first buildup of the then 417 small block (there were 195,000 miles on the car). I believe detonation, possibly due to poor fuel, may have contributed to this failure.

In the image to the right, you can see a crack in the land between the first and second compression rings. It separated from the piston body at the depth of the ring grooves for about an inch to the right of the visible crack.

I first detected this problem by noticing an increase in the coolant temperature during otherwise normal operation of the engine. This was caused by increased cylinder wall friction between the broken ring land and the wall, and probably also between the now slightly misaligned ring and the wall. The ring itself was unbroken.

A second clue came when I observed evidence of increased blowby after aggressive acceleration. There was an oil film around the filler neck and the dipstick had been pushed up out of the tube an inch or so.

I finally confirmed and localized the problem to the number 3 cylinder by performing a compression check. Each cylinder except number 3 read between 210 and 230 psi after turning the engine over several times. Number 3 read only 120 psi. It was time for a rebuild.

Date last updated: June 10, 2003

NCarboni@ProDigitalSoftware.com