View Full Version : Piston to bore clearance with forged pistons...

05-04-2005, 04:02 PM
Hey guys, I am having probelms here!

I have shortblock here, with CAT H-Beams, and Ross pistons (job 69380).

The lady at Ross looked it up for me and told me that the piston to bore clearance needed to be .005.

Big probelm, mine measured from .007-right at .008 amongst the cylindetrs at the machine shop this morning.

How bad is this? I'd assume pretty bad :( Seems they'd be slappin around pretty bad.

The block was bored .030 over form what the machine shop said.

I assume another block would have to be machined to match these pistons... Along with all the other expensive block work...

05-04-2005, 04:48 PM
That's why most good machine shops require the pistons before they will bore a block. There's not much margin for error there, and each brand of piston, and even some sets of pistons can have up to a thousandth difference in between them. When I bore a block (I'm sure most performance builders do the same), I bore each cylinder off of the measurement of a specific piston, and then mark the piston on the top with the bore number in permanent marker. I tend to stay a little small on the boring bar (.004ish), and hone each cylinder individually based on the piston that I marked until I reach the required clearance.