21 stud big bore gasket

flatjack9

flatjack9

Well-known member
Does anyone make a big bore head gasket for a 21 stud engine? I've got a 36LB that is going to 3 3/16 + .020.
 
What are you doing to keep the rings out of the water jacket?, LB blocks get thin at 0.060

Ron talks about using later gasket and making needed holes
 
Will be interested to see if it works for you. I bought a '36 sedan that came with a '36LB block that was made into 3 3/16: cylinder walls bored completely out and machined for sleeves. New cam and valve train was already installed. i assembled the rest of it and put it in my '36 coupe. Got hot right away and spit water out the left header. thought it was a head gasket so tried a couple snake oil "fixes", that didn't work. Tore it down and one of the sleeves was split top to bottom. Bad sleeve??? I don't know, but I later found some info on boring 221 blocks to 239 and it was done with later blocks that had thicker cylinder walls. Good luck. Rod
 
This engine was already bored to 3 3/16 +.010 with very little wear. Sonic testing showed that with a slight shift in a couple bores, it is doable. I'm not doing the work, just suppying parts. Where do you find a LB block these days? Too bad, I had sold one last month and my other one didn't pass the pressure test.
 
I've often heard of '37 to E'38, 21 stud, 221 blocks going to 3-3/16" + some over, but never would have thought a '36LB block would go anywhere near that without doing something out of the ordinary using special sleeves.

In the last five or six years, 36LB engines, with good blocks, seem to be coming out of the woodwork for me, and another local friend. I've stumbled over four, and a friend has found at least three. Prior to that, I couldn't find one good enough to rebuild, or buy one at a reasonable price. Two of mine were basically gifts, and two were in cars I bought.
 
Cometic can do 21 stud gaskets 3.188 bore Part number : H2428SP2040S That is .040" thick, but they can make any desired thickness.
 
With my 3 3/16 bore 21 stud engine, I'm using gaskets that were as big as I could get- not 3 3/16 but...I think from memory I had something like a .007" overhang around top of cylinders. I chamfered the pistons a tad; sufficient to clear, and it works; have not blown any head gaskets. Possibly, using those Cometic gaskets, you'll have in the region of .010" overhang, judicious relieving of edge of piston crowns could get you outta trouble. What are the existing gaskets with the +.010" bore?
 
Brian said:
With my 3 3/16 bore 21 stud engine, I'm using gaskets that were as big as I could get- not 3 3/16 but...I think from memory I had something like a .007" overhang around top of cylinders. I chamfered the pistons a tad; sufficient to clear, and it works; have not blown any head gaskets. Possibly, using those Cometic gaskets, you'll have in the region of .010" overhang, judicious relieving of edge of piston crowns could get you outta trouble. What are the existing gaskets with the +.010" bore?
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Which year 21 stud engine have bored to 3-3/16"?
 
John, It's a 37 block. According to the sonic test performed, it'll go another .020" yet [safely]. Running pump in head heads on it.
 
With MLS gaskets everything has to be dead flat or they leak so surfacing block and heads is a must before using them.
Solid copper and a waterjet cutter maybe...probably cheaper then the MLS from Cometic.
 
Nope but there is a company in the next town with one.
I just send them a CAD file and they cut what i need.
Best would be to O-ringing the engine going for solid copper but that takes CNC macining both head and block...and pinning the head to block for keeping it centered.
Been a lot of questions about bigbore 21 headgaskets lately...wonder what kind of order it would take to make some of the big dragons do a custom gasket run...probably more then hundreds of gaskets...
 
flatheadmurre said:
Been a lot of questions about bigbore 21 headgaskets lately...wonder what kind of order it would take to make some of the big dragons do a custom gasket run...probably more then hundreds of gaskets...
Click to expand...

I need some for .100 over, was planning to repunch 24 stud gaskets.
 
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