Piston clearance

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racyroy1

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Gentlemen,
I’ve got a question about piston to head clearance. I’ve got a set of edelbrock 63cc heads that I want to put on my 340, the pistons sticks up .020 I’m using felpro head gasket .057 thick which leaves.037 before compressed height. Edelbrock says .035 clearance should be maintained at the minimum. Can I run with less clearance or should I go with the 65cc heads?
Any advice would be greatly appreciated.

thanks in advance
Kevin
 
The recommended clearance of .035 is the SAFE clearance. I have ran .025 with a closed chamber with no ill effect.
From what I know now, no need to go under .035. There is no added benefit.
 
Just curious how you checked the deck height,was it with piston rock or tdc?,and are these felpro 8553pt gaskets?.
 
Measure each piston + height to be sure. I run my 340 @.040 quench to 6600K every pass with no issues.


Yeah...my bad. I was ASSuming straight and square decks. That is mandatory to check when you start getting that close. Some guys think a .010 slant in a deck is ok. It's not, but some seem to think so.
 
Don't guess. Use some clay on the piston tops and install the heads and valve train. Rotate the engine through at least 1 full cycle with valves properly adjusted. Section the clay and measure. Cheaper than getting it wrong on start up.
 
Well ok, I checked piston height the first time roughly with a straight edge and feeler gauge that’s where I got my original numbers. I just checked it again with a dial indicator and deck height bridge and I came up with .025 in center of piston and .038 on upper edge at valve reliefs when I rocked the piston.
This engine has about 50 miles on it a quarter at a time. Bottom end is stock except KB HYPER cast pistons. At this point with those numbers I’ve decided to go with the 65cc heads. The numbers are just to close for my liking. Thanks guys for the input and advice
 
Well ok, I checked piston height the first time roughly with a straight edge and feeler gauge that’s where I got my original numbers. I just checked it again with a dial indicator and deck height bridge and I came up with .025 in center of piston and .038 on upper edge at valve reliefs when I rocked the piston.
This engine has about 50 miles on it a quarter at a time. Bottom end is stock except KB HYPER cast pistons. At this point with those numbers I’ve decided to go with the 65cc heads. The numbers are just to close for my liking. Thanks guys for the input and advice
Check this article out and see where the average is at,it may suprise you.If it still isn't to you're liking and you have good enough finishes on the heads and block check out the cometics. I was in the same situation and wound up using cometics.
EngineLabs Blueprint Series: Verifying Piston-to-Head Clearance
 
Funny you’d mention that lead69, I had the original iron j heads on it up until now. I had polished, ported and gasket matched them. I’ve never used aluminum heads until now due to the cost but I had been using cosmetics with the iron heads. That being said I knew I couldn’t use them with the 63cc heads due to the height of the pistons. That’s why I was asking just how tight I could run the clearances, since I had never run aluminum before. Now that I’ve gone with the 65’s I’ll run cosmetics again and calculate the comp ratio over again
 
Cometic can make a custom gasket if needed. costs a few bucks
 
Yeah...my bad. I was ASSuming straight and square decks. That is mandatory to check when you start getting that close. Some guys think a .010 slant in a deck is ok. It's not, but some seem to think so.
Is a amazing what some machinists will do and stamp it OK and good to go.
You'll be fine unless you have excessive piston to wall clearance. Like making noise when cold sloppy. If not, you're good to go.

The recommended clearance of .035 is the SAFE clearance. I have ran .025 with a closed chamber with no ill effect.
From what I know now, no need to go under .035. There is no added benefit.
And what these guys said above. The above mention of the cometic gasket is what I have done several times. There really is t a need to get super close but keep the quench under .050. It’ll be fine. Setting the quench super close is starting to gamble on everything else being great.
 
And what these guys said above. The above mention of the cometic gasket is what I have done several times. There really is t a need to get super close but keep the quench under .050. It’ll be fine. Setting the quench super close is starting to gamble on everything else being great.[/QUOTE]


That’s why I decided on 65cc

and just to clarify, I know the word is “cometic”, the spell check got me
 
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