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Old 05-13-2007, 07:20 PM   #1
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302 piston to head clearance???

Hi All,

I am in the process of installing my TFS TW Track Heat heads, TFS Stage 1 cam and TFS billet timing chain at the moment and I mocked up the head with clay to check the valve to piston clearance and lo and behold, the engine would not turn over, locked up solid at TDC #1 piston... When I realized what was happening, I then put the Felpro 9333 head gasket in place and checked again, sure enough, the engine turned over fine. The shortblock is a bone stock 75k mile '88 GT piece that has never been machined or apart. Are all 5.0 engines positive deck, or do I have a problem here?
What is the allowable piston to head clearance on a SBF Ford engine? I believe the head gasket is .040???

Thanks for any help in advance
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Old 05-13-2007, 09:53 PM   #2
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Hi Brad,

No, the engine was bone stock, never machined with std bore 4 valve relief forged pistons. So, assuming a Felpro 9333pt1 head gasket is .040 thick compressed, is that good enough (keeping in mind that the piston comes out of the block far enough that it will not allow the engine to rotate without a headgasket in place)?
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Old 05-13-2007, 10:56 PM   #3
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My pistons were out of the hole stock also; mock it up with a used head gasket torqued to about 50. Measure your p to v. Also measure how far out of the hole the pistons are. Subtract it from the crushed head gasket thickness (they usually come in .039" and .041" varieties) for your quench dimension. .035-.040" is good for a street engine. It went 75k miles with this quench dimension -- measure and you'll know what you're dealing with. All you know right now is that the pistons are out of the hole.....doesn't really tell you much.
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Old 05-14-2007, 04:34 PM   #4
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All 8 of them were out of the hole Brad.

Don't know what 'normal' is --- my engine is the only one I've measured....
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Old 05-14-2007, 07:00 PM   #5
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9333's are .047" compressed just for reference....
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Old 05-14-2007, 07:07 PM   #6
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you beter look again.


the piston itself DOES NOT HAVE TO stick out of block to hit the head.


oftentimes the valve can slightly stick out beyond the flat deck surface ( gasket surface) and THAT it what is hitting the piston.

#1 thing is,
something is hitting something.

A) pistons STOCK have been found below the deck...above the deck....and right even with the deck on stuff from the factory.

...it is all a combination of tollerances...some connecting rods could be longer or shorter...some pistons could be longer or shorter........and the block itself could be shorter or not square...

make certain that the "test gasket" is on in the correct direction... the BORE holes are NOT symetrical with the tube-dowel locators on the end-corners of the block......the end marked FRONT....is still the front.... and is allways front .....even if upside down....
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Old 05-15-2007, 11:44 PM   #7
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OK, Thanks for the reply guys.

I was at the garage tonight and went over the issue with my trusty Starret dial indicator and deck bridge. The #1 piston pops up about 6 thousands of an inch. The rest of the pistons on the bank are all within the same specs (#1 is the highest though). I talked with a tech at TFS and he said .030 clearance is enough for a street engine??? So, with a compressed thickness of .047", I should be fine
The head gaskets are in the correct position with the label "FRONT" facing the front

I have built many big block Mopar engines, and this is my first small block Ford build up (have owned many 5.0 Mustangs, but never this far apart), with the BB Chrysler engines, the pistons are almost always WAYYYY down in the hole and new pistons and (or) decking is the way to fix that.
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Old 05-16-2007, 07:39 AM   #8
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If you use a .041" gasket, that'll put your quench right at .035" which is just about as good as it gets. I'd use that instead of the .047".....
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