BSA A10 1960 Spitfire Scrambler - Engine Head Gasket Question

[Superarnie]

Hello to you all. By way of introduction, I am currently restoring a 1960 Spitfire Scrambler, it has been a full nut and bolt restoration and I am in the final stages of the engine assembly. It has been a really enjoyable project and I will post some images in due course but I have a general query that I'm hoping you might be able to help me with. When I stripped the engine down it had forged 10.5:1 compression pistons. On the rebuild I have fitted GPM 8.5:1 pistons (60 thou over sized). The alloy cylinder head had to be skimmed and 24 thou was removed. Can anyone tell me if I could still use a standard thickness copper gasket which I think is 1mm in thickness or would I risk valve interference? Following an internet search I have found a company in Canada that can supply me with a 2mm copper gasket, however if I could still use the standard one I'd prefer that, appreciating the CR will be raised a bit. I understand the carbon fibre gaskets are a little thicker, but I have read mixed views about using them so would prefer to stick with copper.
Many thanks in anticipation of your advice
Gary

[chaterlea25]

Hi and Welcome Gary
I would do a trial assembly with placistine on the piston crowns so that you could check the clearances between the
valves and pistons and pistons to the head
Copper gaskets unlimited in USA will supply copper gaskets in several different thicknesses and make them to the bore size needed
I did fit a 2mm gasket to one engine where the head was heavily skimmed but that had flat topped pistons
No issues with the 2 mm gasket since

John

[muskrat]

G'day Gary 
I agree with John, best to do a dry run.
I have also used Copper gaskets unlimited https://coppergaskets.us/shop/ols/categories/bsa-motorcycles to make modified head gaskets for my two A's.
I'm assuming the motor has a 357 cam. With 8.5 pistons I don't think you will have a problem with a standard gasket.
I had forged 10.5's and 357 in my A10 Cafe with std gasket.
Cheers

[Rex]

Use Plasti-gage to get an accurate measure of the piston clearance.

[Joolstacho]

And do a 'reality-check' measurement of the compression ratio while you're at it eh?

[Superarnie]

Thanks to you all for your contributions, they are very much appreciated. I take it I would need to assemble the head and rocker box, and rotate engine by hand in order to check for indentations in the plasticine? And presumably, the rocker gaps set correctly?

[muskrat]

G'day Gary.
Yes that's right. A PITA but necessary. A clearance of at least 0.060" between vales and piston pockets.
 Another thing to check is at full lift the valve must be able to push in at least another 0.060" before it gets coil bound.
Cheers

[Superarnie]

Thanks very much. I'll give it a go!

[Klaus]

I use 0,7mm copper selfmade gaskets on 9.0 to 1 compression with no problem, since many years.

cheers Klaus

[Superarnie]

Hi there, by way of update from my original query, I contacted Copper Gaskets in the States and bought a gasket at 63 thou. Their service was first class; great communication, prompt dispatch, really pleased. The gasket arrived and has been annealed and fitted.
Thanks to everyone for their contributions.
Regards
Gary