Over size pistons help.

[tguss]

Question what is measurement on a 30 over 360 piston ? Is it 4.030 ? Or is the 4.030 the bore size for the piston ???

 

[80fbody]

Each manufacturer is different. Pick a piston then call them & ask for an actual skirt measurement. These days most manufacturers include the clearance in the overbore size. So with a 4.030 bore, the piston will show up 4.025 (5 thou under). Thats just a scenario. Always best to have pistons in hand before boring/honing block.

 

[perfacar]

hi, 4.03 refers to bore size, pistons are slightly smaller. usually .001 to .003 depending on stlye of piston. forged usually have more clearance. the clearance is made in the piston

 

[pishta]

Bore size: bore is honed for piston size usually within .001 of piston skirt size. Crown of piston is smaller than skirt you may find some dimensional drawings on a piston makers are like probe or wiseco.

 

[tguss]

I have a block and bore is reading 4.040 is this bore to 40 over pistons ?? Thanks for all the help

 

[80fbody]

Correct .040 over. Are all bores straight (no taper)? If not you'll probably need to go up to the next size .060 over.

 

[80fbody]

Bore size: bore is honed for piston size usually within .001 of piston skirt size. Crown of piston is smaller than skirt you may find some dimensional drawings on a piston makers are like probe or wiseco.

I'm no machinist but....Not so sure about tossing that out like that. Piston manufacturers typically spec their size & clearance based on the skirt (widest part). Some have different location but 1/2" up is what I've done. 1 thou clearance & you're going to lock a race piston right in the bore as soon as it warms up.

 

[RustyRatRod]

All of the piston sizes refer to the bore size. The pistons are generally around .005" less than the bore size. So, a .030 over 360 piston may measure 4.025". This is why you measure a piston, bore a hole and repeat.