So I have my 3VZE block at the machine shop to get bored out and have a new set of NPR 1.0mm/.040in over-sized pistons installed and they asked for the piston-to-bore clearance or oil clearance spec. I gave them the number in the factory service manual which is also listed in the Haynes manual of 0.13-0.15 mm/0.0051-0.0059 in. They thought this was pretty high and stated they usually see at max about 0.002-0.003 of clearance total for engines like this so that is 0.001-0.0015 per side. The factory spec of 0.0051-0.0059 in. is something they typically only see on forged pistons for high boost or nitrous engines. Has anyone else ran into this? If so what was your resolution? I'm leaning toward going with the machine shops recommendation unless there is a good argument not to.

 

I haven't looked at the FSM, but I'd guess that the .0051 to .0059in is the service limit spec, where anything more indicates the necessity of new parts, or rebore.

The machine shop suggestion of initial clearance of ..002-.003in sounds right for a tight engine. Careful break-in will be in order

 

Oddly enough this is not the service limit spec. That is specified as being 0.17mm or 0.0067 in!!

 

A couple thousandths between fresh built and service limit sure isn't much.