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mbarjbar

Piston to head clearance?

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I just got my short block back from the machine shop. He installed flat top pistons that have valve reliefs. At TDC, the piston top is 0.009" higher than the block deck. Is this acceptable on an early L24. He took 0.005" off of the deck and the head. :paranoid:

Thanks,

Mike:ermm:

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Flat tops with valve reliefs (73 pistons)come out of the block .030 inches. Gasket crush is .060 inches. Dave Rebello told me that they like .060 inch clearance between the piston and head. The way I understand it is that people install them all the time with no problem, but I shaved .020 inches off of my pistons just to be sure. The amount shaved off the head has no effect. The .005 inches off the block is no help. Are you sure you only came out .009 inches? Lay a feeler gauge on the block to measure the distance. Let me know what you come up with.

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How do we know he installed 73 pistons?Did your machinist cut some small reliefs in your pistons?

From what I read, with a stock Nissan gasket( .047 or 1.25mm) he would be around .035 head to piston clearance, which is good for squish.

That is what I am running. I had .005 taken off the deck and stock piston height--no problems.

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Steve......The pistons that were fly cut from the factory......They are 73 pistons......they come out of an uncut block by .030 inches which is OK if you have the open chamber E 88 head. If you are running the early E 88 or E 31 head, you are within .030 inches of contacting the head. Any rod stretch could cause contact (maybe). But many people are running them with no problem. If you are racing and down shifting to 7 or 8 thousand rpm, it could be a problem. Street use....shouldn't be a problem.

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I measured by laying a straight edge on top of the pistion and with a feeler gauge, measured the gap between the bottom of the straight edge and the deck. The 0.009 blade just fits in the gap. It sounds like I won't have any issue with piston to valve or head contact.

The pistons came with the reliefs already cut.

Mike

Edited by mbarjbar

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I wouldn't give that a 2nd thought..........Where did you get your pistons?

Edited by Diseazd

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I went back and reset TDC more accurately. I now have 0.015 difference. Still should be ok. Thanks for all the input.

Mike

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