Head gasket help

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James Hurt

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My pistons have a positive deck height. Icon 745 pistons, Molnar 6.123 h beam rods,Molnar 4” crankshaft. Pistons are .018 out of the block. Bore is 4.080. Using Speedmaster heads. I know quench height is critical. Would a .040 compressed head gasket be sufficient?
 
James Hurt said:
My pistons have a positive deck height. Icon 745 pistons, Molnar 6.123 h beam rods,Molnar 4” crankshaft. Pistons are .018 out of the block. Bore is 4.080. Using Speedmaster heads. I know quench height is critical. Would a .040 compressed head gasket be sufficient?
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Probably NOT
 
That would be .022, WAY to close. Use the fel pro gasket that's like .053 compressed, will be safer. Also check all 8 pistons, unless the block was square decked, they wont all be the same either.
 
Felpro make a head gasket thats 0.054" compressed, I believe they list it for marine applications.
Edit - not the marine gasket, Felpro part no. 521SD.
 
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replicaracer43 said:
That would be .022, WAY to close. Use the fel pro gasket that's like .053 compressed, will be safer. Also check all 8 pistons, unless the block was square decked, they wont all be the same either.
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I’ll check all of them after work tomorrow. Thanks.
 
replicaracer43 said:
That would be .022, WAY to close. Use the fel pro gasket that's like .053 compressed, will be safer. Also check all 8 pistons, unless the block was square decked, they wont all be the same either.
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The part number on those are 8553pt
 
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Thanks for the recommendations. I’ve purchased some different measuring tools, bridge and dial indicator from summit. I’ll be remeasuring the piston protrusion tomorrow. Thanks for the information.
 
Ted265 said:
Felpro make a head gasket thats 0.054" compressed, I believe they list it for marine applications.
Edit - not the marine gasket, Felpro part no. 521SD.[
I remeasured my piston protrusion. It varies from .015 to .023. What is the minimum quench I can safely run? I have the 521sd head gaskets.
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depends... you can tap heads with forged pistons and live if it ever grew to that...but hypers will shatter if they touch.

If building a real quench motor...I'd stay .029-.035 . No less, no more.
 
MOPAROFFICIAL said:
depends... you can tap heads with forged pistons and live if it ever grew to that...but hypers will shatter if they touch.

If building a real quench motor...I'd stay .029-.035 . No less, no more.
Click to expand...
MOPAROFFICIAL said:
depends... you can tap heads with forged pistons and live if it ever grew to that...but hypers will shatter if they touch.

If building a real quench motor...I'd stay .029-.035 . No less, no more.
Click to expand...
MOPAROFFICIAL said:
depends... you can tap heads with forged pistons and live if it ever grew to that...but hypers will shatter if they touch.

If building a real quench motor...I'd stay .029-.035 . No less, no more.
Click to expand...
Forged icon 745 pistons, molnar h beam rods and molnar forged steel crank. With the 521sd head gaskets should be .031 on the highest pistons.
 
That could be the rods, resized/ slightly diff lengths, deck squareness as well, as well. Good mention.

Another note, the P/H clearance I mentioned accounts for the skirt clearance. Piston rock is only half of the total.
 
Those are pretty much the exact same numbers as my 340 KB 243 Pistons I run 0.50 steel layered gaskets and I wouldn't go any tighter. Let's just say there's no carbon on the top of my Pistons.
 
James Hurt said:
Yes. Read it. I’m measuring 90 degrees from the wrist pin. Tried to rock the pistons with the bridge installed. Couldn’t get them to rock. I’ve read where folks run .027 quench. Could I get by with.031 with forged pistons?
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I treat the 745s as domes and measure off the quench pad, rock the piston up and down and half the total measurement is the deck height.
 
lead69 said:
I treat the 745s as domes and measure off the quench pad, rock the piston up and down and half the total measurement is the deck height.
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Learn something new everyday. I now realize what piston rock is. Will get the average on each cylinder and compare. Thanks.
 
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