Thicker head gasket for CR recessed block

[Steve Morris]

As above, any recommendations for sourcing a thicker head gasket would be very useful.

I have tried Cometic but am not getting any response from them.  It looks like they only do the thicker head gasket for the earlier flat block.

A very smart friend has calculated my CR as being 10.6:1 and I would really like to bring this down to 9.5 - 9.75:1 if possible.

Edited October 3, 2025 by Steve Morris

[Malbaby]

4 hours ago, Steve Morris said:

As above, any recommendations for sourcing a thicker head gasket would be very useful.

I have tried Cometic but am not getting any response from them.  It looks like they only do the thicker head gasket for the esrlierflat block.

A very smart friend has calculated my CR as being 10.6:1 and I would really like to bring this down to 9.5 - 9.75:1 if possible.

Has your friend calculated how thick a gasket is required to achieve the desired CR.

Apart from having one custom made [expensive], you could use two gaskets.

You will also have to check the valve train geometry after fitment.

[Waldi]

Another head could also be an option, if this one is too much skimmed. That would be a permanent solution. 

Revington (and others) sell solid copper gaskets up to 1.5 mm, not sure if they would be ok for recessed blocks:

https://www.revingtontr.com/product/rtr1489-1.5k/name/head-gasket-copper-15mm-thick-fi-tr25056

Waldi

[Steve Morris]

8 hours ago, Malbaby said:

Has your friend calculated how thick a gasket is required to achieve the desired CR.

Apart from having one custom made [expensive], you could use two gaskets.

You will also have to check the valve train geometry after fitment.

Thanks for your reply.  

 

He actually thinks 10.6:1 static is ok on the long stroke engine.  I’m just a bit nervous about that myself. 
 

I think that a thicker gasket will improve valve geometry in my case as the pushrods are standard length, bizarrely.  
 

Would a double gasket solution be potentially weaker?  
 

it may be a case of just moving this head on I think.

 

[Steve Morris]

1 hour ago, Waldi said:

Another head could also be an option, if this one is too much skimmed. That would be a permanent solution. 

Revington (and others) sell solid copper gaskets up to 1.5 mm, not sure if they would be ok for recessed blocks:

https://www.revingtontr.com/product/rtr1489-1.5k/name/head-gasket-copper-15mm-thick-fi-tr25056

Waldi

Thanks Waldi - Revington do have a thicker copper gasket - up to 2mm I think but it is very expensive - still an option though.

[Steve 286]

Have you checked the head thickness as a standard early head with part number 516816 is 3.400 inches thick and the later heads including some pi can be thicker around 3.500-3.550 inches thick 

[Steve Morris]

Hi Steve, yes I have it’s around 3.350 - have also buretted the chambers.

[Steve 286]

My cylinder head is 3.300 but it has been ported 

[Steve Morris]

Ah - any issues with pinking or is it fine?

[Steve 286]

It runs fine but I use e5 fuel and I had Martin rebuild the distributor 

[Phil Kirk]

13 hours ago, Steve Morris said:

Thanks for your reply.  

 

He actually thinks 10.6:1 static is ok on the long stroke engine.  I’m just a bit nervous about that myself. 
 

I think that a thicker gasket will improve valve geometry in my case as the pushrods are standard length, bizarrely.  
 

Would a double gasket solution be potentially weaker?  
 

it may be a case of just moving this head on I think.

 

Steve on the for sale wanted Trseks is offering a TR6 cylinder head for free. Looks like it could be what you are looking for?

Cheers Phil

[Steve Morris]

Phil, that’s an incredibly timely heads-up!  I owe you a pint.