69 Z28 head gasket - Team Camaro Tech
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post #1 of 12 (permalink) Old May 31st, 15, 09:41 AM Thread Starter
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MIKE
 
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69 Z28 head gasket

I am rebuilding the 302 engine in my 69 Z28, what is the original factory head gasket thickness,, was it a steel shim gasket.

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Mike
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post #2 of 12 (permalink) Old May 31st, 15, 10:12 PM
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Re: 69 Z28 head gasket

Yes, the original was a steel shim gasket.

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post #3 of 12 (permalink) Old Jun 1st, 15, 06:30 AM
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Re: 69 Z28 head gasket

.017 to .019 as I recall.

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post #4 of 12 (permalink) Old Jun 1st, 15, 07:43 AM
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Re: 69 Z28 head gasket

Hey Mike:
Yes, as Jon said, the original was a steel shim type.

How far down in the hole are the pistons?
Factory pistons?
Are all 8 the same, or at lest close to the same?

Lynn
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post #5 of 12 (permalink) Old Jun 2nd, 15, 01:07 PM Thread Starter
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Re: 69 Z28 head gasket

Pistons are down .007-.008, block was decked so all are very close to same,
bored .030 w/ 11:1 trw's , using the GM #140 offroad cam, I checked clearance w/ no head gasket installed and have good clearance, I am looking at Cometic .030 compressed which will give a quench of .037-.038, maybe I should use a thinner gasket, how tight can I go on quench
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post #6 of 12 (permalink) Old Jun 2nd, 15, 02:16 PM
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Re: 69 Z28 head gasket

You are about as tight as you want to go with the old TRW's (I am guessing the forged piston, running at least .004 clearance). Smokey Y used to say .005 to .0055. Other builders disagree. Frankly, I am afraid to run the old forged at less than .004. You get some piston rock when cold. Shouldn't be enough to cause the "slap" sound, but may get close to the head until warmed up.

The old "rule of thumb" is .010 for each inch of bore size. I have cheated a bit closer with forged TRW's at .035 on a 4 inch bore and gotten away with it each time. Can't promise though.

Again, this assumes forged slugs.

Lynn
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post #7 of 12 (permalink) Old Jun 2nd, 15, 02:40 PM
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Re: 69 Z28 head gasket

Here are two sets of head gaskets that will work with the distance the pistons are down in the hole. http://www.jegs.com/i/Cometic-Gasket...ductId=2848865 and http://www.jegs.com/i/Cometic-Gasket...ductId=2848865 These are one of the best gaskets made and they are MLS gaskets.
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post #8 of 12 (permalink) Old Jun 2nd, 15, 08:49 PM Thread Starter
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Re: 69 Z28 head gasket

Thanks for all the response & info. ,
The machine shop set piston wall clearance at .004 ,
I ordered Cometic 4.060 bore, .027 compressed thickness, this will give .034 to .035 quench area, the #140 cam has a lot of overlap & duration to bleed off a little compression, the tight quench helps prevent detonation, I have built several 302 engines over many years using these tolerances and had very good performance and all were very reliable,

Last edited by miket1; Jun 2nd, 15 at 09:09 PM.
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post #9 of 12 (permalink) Old Jun 2nd, 15, 09:14 PM
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Re: 69 Z28 head gasket

I think you are right on.

Take a video clip when you get her running. I want to hear it.

Lynn
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post #10 of 12 (permalink) Old Jun 2nd, 15, 10:12 PM Thread Starter
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Re: 69 Z28 head gasket

OK Lynn, I will try to get that, it may be 6 weeks or so before all completed.
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post #11 of 12 (permalink) Old Jun 19th, 15, 02:33 PM Thread Starter
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Re: 69 Z28 head gasket

My 302 is assembled w/ all the original internals and other stuff it was built with and almost ready to install, still need to paint it and install new clutch ,maybe couple weeks out.
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post #12 of 12 (permalink) Old Jun 19th, 15, 04:08 PM
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Re: 69 Z28 head gasket

Quote:
Originally Posted by miket1 View Post
block was decked so all are very close to same,
I hope they didn't mill off the block numbers ?

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