Positive deck clearence

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Jul 16, 2008 | 08:25 PM

Goose_52

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From: Duluth MN

Positive deck clearence

I have a set of TMI 9.5:1 CR pistons in my block, and while degreeing my cam today, I noticed the high side of the piston(near the valve relief) is about .008 above the deck. Is this supposed to be like this? I cannot imagine it would be. I know this block has been rebuilt previously, now I am wondering if the machine shop decked the block too much. I will call Tim tomorow and get his input, but maybe one of you guys would happen to know also.

Jul 17, 2008 | 01:33 AM

hollenjoe

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hmmm i gave thought to this and i asumed tims pistons are not exactly 10.297" due to the fact that most rebuilds take a bit from the deck and heads, its not that bad to have your pistons that up, but you have too watch yourself for compression and cam choice....when doing such choice make a post....

Jul 17, 2008 | 11:28 AM

beartracks

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From: Albuquerque

I'm not sure if the combustion chamber can take that or not but at 9.5 to 1 you should still be noticably donw in the cylinder.

Jul 17, 2008 | 03:47 PM

80broncoman

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From: southeren Oh

.008 is no problem at all as to having enough room.

I just got my TMI pistons in my block (in a engine that also has been a remaned unit) and one of mine is about .012 above the block. I going to run this way. The rest of mine range from Zero to +.010
I have seen plenty of engines built using flatops up .015 out of the block with a .045 headgasket. It will raise compression slightly.

Jul 17, 2008 | 10:29 PM

TMI

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From: Fairmont

Those pistons have a comp height of 1.710" this theoretically will give an extra
.010" for resurfacing. We have seen the 400 engine deck height being way off.
By time you get you block flat and even bank to bank, we have seen it down .010"-.015" below the "Zero"

Also crankshaft grinding can change either way if not watched.

Jul 18, 2008 | 09:48 AM

beartracks

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From: Albuquerque

I'm not familiar with the pistons but wont they hit the head if they protrude out of the cylinder?

Jul 18, 2008 | 02:47 PM

80broncoman

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From: southeren Oh

Quote:

Originally Posted by beartracks

I'm not familiar with the pistons but wont they hit the head if they protrude out of the cylinder?

If you are refering to a stock 400 head it has a large open chamber so no chace of it on that one.

If you are refering to my statement about other engines being built with flattops out of the block, a normally thick gasket (not a thin race gasket) will will be thick enough to keep head from making contact.