Aluminium head gaskets

[Alan]

As long as you have clearance for the valves, would you not be better putting a compression plate under the block? These are still available I think and you would be able to use a normal copper composite head gasket.

[JonE]

Alan - does the above mean that in essence the pistons aren't coming up as far, so the reduced CR is the same where-ever you put the filler in the sequence?

[Alan]

Not quite. If you put the spacer under the head you also increase the volume of the valve space, so the loss of compression will be greater. However, there are other reasons why you might want to put the spacer under the block. Having a gap between piston and head is beneficial to flame travel, and therefore probably thermal efficiency. If you can achieve this without increasing your valve space so much the better.

[Ian Williams]

I would suggest that the transfer port will be very restricted in a head that has been skimmed so much that a spacer is required to restore the CR. The transfer port is often quite restrictive in A7 head designs and only made worse as you remove material from the head face.

[Nick Lettington]

Thanks for the comments Ian and Alan, both are very useful. Just to add another layer of information,  the original design of the Speedex head pictured below (not mine) incorporates a space above the pistons. This is not carbon build up before you ask, but the edge of the recess.


  Screenshot_20220823-080900_Gallery.jpg (Size: 216.18 KB / Downloads: 217)

[Chris KC]

That Speedex head looks different from mine - though I do remember it ran pretty well. 
I'd echo Ian's earlier comments, with any solid gasket you will likely spend a lot of time chasing water leaks. I'm not sure there's a real benefit vs a C&A type, personally I don't have any big issues with these so far.
I have run several engines with aluminium spacer plates under the block and these are not hard to make by hand (I'm using Reliant rods so they are 1/8" thick or thereabouts). Of course the number of oil leakage paths is increased accordingly but with silicone sealant it is manageable.

[Nick Lettington]

I have yet to assess the valve travel, but having inspected and measured two heads it appears the bad one has had in the order of 0.100" removed, possibly more on the basis that the thicker one also has clear signs of skimming... 

That's rather a lot of metal... perhaps I'd be better off taking my own advice (re speedos) and getting rid of it in favour of a better one. Silk purses, pig's ears and all that..!

Still interested to know if anyone has experience of metal spraying in such circumstances. There's a little bit on the net to suggest that might be a possibility..?