Hitchcocks Forum

Hello been away for a while, mainly because the battery of my caliper was dead. I measured my piston today, it sits at 69.19mm, but I can't seem to find accurate information about what size it is supposed to be. Is this an oversize? or stock? thanks!

Again, forgot to add...1955 350 bullet G2.

69.19mm seems under-size! The standard size piston for a 350 is 69.874mm - or should be somewhere near that!
(Not sure what the battery has to do with a caliper - but there we are!)

I don't trust electric guessing sticks, you really can't know if they are reading properly.
I much prefer good old fashioned ones.

However, what does the bore measure?

I don't have the equipement to measure the bore. All I know is the piston rings are within clearance spec. that's what my manual said as well. Undersize seems extremely strange indeed...

Are you sure? As the others have said, STD is 69.874 but that is widest point, bottom of skirt should measure 69.811 fore and aft so still not close to your measurement! However, the piston to bore clearance is what matters and should be about .006" measured at bottom of piston skirt at front or back so if that's ok, I'd live with it. My 55 350 Bullet didn't have a piston in it so I can't compare!

REgards, Mark

I went and brought the piston here. At the bottom of the skirt it read 69.78mm...I must have taken the measurement wrongly. I measured the first time right above the first piston ring at the top.

The top of a piston where the ring grooves are is quite a bit smaller than the skirt, because the thicker alloy there expands more than the skirt. It gets hotter too, the main reason for the difference. Always measure piston to bore clearance front to back on the skirt, and near bottom of bore.