Piston to head clearance issues, got a few questions.

[flyboy01]

I have some questions regarding piston to head clearance. I have a 383 block that had the decks cut to make them true, I hade about .040 cut off, now with a different setup (440 crank, B rods, Diamond forged pistons) my pistons come out of the hole about .020. I have .039 head gaskets now, will they give me enough clearance or should I get some thicker Cometic gaskets?

[william]

With an open chamber head you should be good but with a closed chamber head a 0.060" gasket

[buck440]

 

[farmington]

You're probably gonna have rather high compression, so a .060 head gasket should work pretty well.

[flyboy01]

Sorry, should have mentioned, I have stealth heads. So I am assuming from your answers that I need a min of .040 piston to head clearance?

[oldkimmer]

....................................U got it.....................kim..................

[satellite65]

.040" is ideal for proper quench with .030" being the minimum. I've read somewhere that .020" is the absolute minimum you could have before you start having parts say 'howdy' to one another, and that's assuming very tight bearing clearances. You're at .019"? Better get some thicker head gaskets.

[flyboy01]

Should I get the cometics or is there another head gasket that comes thicker?

[smallbigblock]

I believe that Cometic's can be ordered in several different thicknesses,

Here is FBO's web page - these guy's are great
http://www.4secondsflat.com/partsindex.htm

[flyboy01]

Damn those things are expensive! $250. Pair!

[satellite65]

FBO's website says $151.95 / pair. Still not cheap but probably less expensive than having all 8 pstons milled down.

[oldkimmer]

................I think felpro has a .051 gasket....................prolly not enough though...........kim............

[68 HEMI GTS]

yea id stick a .060 on it.

[flyboy01]

FBO's website says $151.95 / pair. Still not cheap but probably less expensive than having all 8 pstons milled down.

Oh well, in for a penny...in for a pound.

[tnplumber]

Glad to see that your still working on the '68.   

[smallbigblock]

Damn those things are expensive! $250. Pair!

They arn't cheep, but they are reusable. 

[flyboy01]

thats good, i am going to do the final assembly and take some measurements before I order them. I amost got the motor assembled last night, then I was torning it over to install the 7th piston, then...clunk...it stopped. Rod nut hit the bottom of one of the cylinders.  I took out all the pistons yesterday and I am going to clearance grind all cylinders.

[farmington]

Since its not together, why not mill .020 off of the tops of the pistons?  That would be a rather simple way to go.  contact your piston manufacturer and see if they're ok with a little milling.  .020 is only like 6 sheets of notebook paper thick.  the pistons won't even miss it.  Shouldn't affect balance either.

[satellite65]

There's a good idea. Then you're back to good old fashioned, off the shelf gaskets.

[flyboy01]

I actually have it all back together, I did the final measurements, checked all the pistons, min is .015 and max is .025, so I am going to order a set of .065 Cometics. Right now the short block is all together. Degreeing the roller cam tomorrow mornignand measuring for pushrods. I hope to fire the engine on a test stand in the next couple of weeks.

[bOb shingler]

remember now that with all that milling and a .065" head gasket your heads will be +.025" higher than stock. my suggestion is to make sure the intake sits on correctly. when you order the bathtub gasket get the felpro one that comes with the 4 thin paper intake gaskets so you can get everything aligned back up. this way you have the option of using none, 2 or all 4 to get it correct.

[the nitro man]

do you know the part number on that gasket?

[Tiamat]

Fel-Pro Performance Z1215  Summit has them

[flyboy01]

I am not using a valley pan, I am using a 2 piece steel valley cover from Hughes with their thick silicone faced intake gaskets. Since i have milled so much and using thicker head gaskets, it should put the heads back near the stock position. Of course, being aftermarket parts, it's all relative anyway.

[flyboy01]

I ordered a set of .070 cometics today, $220.00 shipped. I figured highest piston at .025 + .040 quench + .005 for fudge.

[satellite65]

Just a quick question, do your heads and decks have the correct finish for Cometics? From what I understand they want a really smooth surface in order to seal properly. I'm in the same boat, only opposite. My pistons (speedpro 2355 six pack pistons w/valve reliefs) sit .016" below deck. Gives me a perfect 9.6:1 CR with my 906 heads. If I upgrade to Stealths or Eddy's I'll have too much room for proper quench with conventional gaskets. I can get Cometics made thinner but my surfaces are a little rough for them, supposedly. If I'm going to have my deck re-surfaced I may as well just zero deck the motor, go with FelPros and be done with it.

[bOb shingler]

spray them with copper coat.

[68 HEMI GTS]

spray them with copper coat.

   i actually cut the rivets and spray both sides of the sealing surfaces.

[flyboy01]

My decks are very smooth, good tip on the copper, I will do that.