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head gasket for 400 big bore

  • Thread starter Thread starter costa
  • Start date Start date
C

costa

Guest
Right so iv currently located everything to do the big bore kit on my 400 except a head gasket. Will be using Weisco pistons at 69mm and my current bore is 65mm. Now a cometis copper one in the uk is well upwards off ?100 which is more than my budget. I have got a brand new head gasket which came in the kit which measure 68mm across. My question is would a 425 head gasket work? If the pattern continues is it going to be 70-71mm. This is currently the only thing stopping me from ordering the piston kit and getting the machine work done.

Thanks in advance
 
The gasket for the 425 is only 67mm. that would leave 1mm of gasket inside the combustion chamber.

I think the fiber gasket from cometic would work just fine for this.
And since there are already two members here that have done it, cometic should have the gasket CAD drawing already. Might have to play around with the years and engine sizes though.
like 78, 79, gs400 roller. or 79 gs450 .. It all depends on the person making the gasket and what they record it as. mine was recorded as a gs450 when it was made although its the same gasket, mine is actually 548 and started off as a 400.

If your stuck then just go it alone and make one yourself out of copper sheet.
Use your head gasket and trace it out and then drill only the outside hole's.
Then flip it over, put your cylinders on it and line up the holes. After they are lined up just trace the inside of the cylinders and cam chain tunnel to your new gasket.

Start drilling and take your time. File down the rough spots and keep shaping it until your happy.

might take a few times to get it right.

You end up with something like this
7284006832_89ce8b6ce8_b.jpg


This is a base gasket I made for mine with just a step drill and hand file.
Took 7 tries before I found a perfect way to do it.
 
Last edited:
cheers for getting back. ill try get some copper sheet. How did you get it to 548cc?
 
ill get reading cheers. Iv managed to find copper sheet at 1.2 mm thick for reasonable price. how much does the copper squash . as in should I make the cylinder holes slightly larger on the gasket to compensate?
 
costa said:
ill get reading cheers. Iv managed to find copper sheet at 1.2 mm thick for reasonable price. how much does the copper squash . as in should I make the cylinder holes slightly larger on the gasket to compensate?
Click to expand...

Make it the exact size of the bore.
After your done making it you have to aneal the coper and that will harden it. then use some Coper coat as a way of sealing it.

I was even going to use an aluminum gasket since It was easy enough to get the material and make it.
 
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