cam_arrow

I have a iron 6.0L block that was advertised as being a 4.030 bore. One would think I would have to order pistons 0.30 over After measuring cylinders (which are finished honed) I get a bore of 4.0261 to 4.0274. Is this normal or are they way off on their machining? On one hand…. the pistons I want to use GMPP 89017479 - LS-Series Piston are 0.020 oversized and if within tolerance will give me a pretty good piston to wall clearance. On the other hand… if the bore was 4.030, wouldn’t 0.030 oversized pistons not work.
I know most people finish hone to the pistons, but what do these manufactures that finish hone their blocks expect the customer to do? Any encounters welcome.

turbotbirds

I always get the pistons and then have the bore matched. I would take that block to the machine shop and let them measure it and tell you which oversize to get.

cam_arrow

confident on my measurements and piston selection…would use the pistons mentioned instead of taking a block to a shop…kinda makes more cents$.

KCS

iTrader: (20)

Pistons sizes are for the bore. For example, 4.030" pistons will actually measure approximately 4.026" so the clearance is built in already.

I would get the cylinder rehoned. Over .001" tolerance (4.0261" - 4.0274") is pretty sloppy.

cam_arrow

thanks KCS...thats exactly the feedback i was looking for. so .020 pistons from GM are going to be around 4.016?