XK head skimming limit

[bigcat1]

I'm in the process of overhauling the cylinder head on my 3.4 1961 Mk2. I'm checking the flatness of the head face. I might need to have it skimmed, but I know that a previous owner had it skimmed in 1995. I have no idea how much was skimmed previously or whether it had been skimmed previous to that.
So, there must be a limit to how much a head can be skimmed before it can't be skimmed anymore. But does anyone know what that limit is and is there anyway to measure it? Is there a datum point that one can use as a measuring point?
Also, I can see that there is a composite head gasket available that is 1.8mm thick. SNG Barratt website advises that this should only be used on a head that has been skimmed. Has anyone used one of these gaskets?
Many thanks

[piman]

Hello Bigcat1,

Des Hamil in his book on the XK states that they can be skimmed up to 0.040" to increase compression if desired but refacing for flatness should be the minimum possible. He also say if there has been overheating and the head had warped in the past and refaced it is worth fitting the camshafts, with the valves removed to check that they turn freely. Heards can warp to such an extent that the camshafts bind as the cam bores are no longer true.

Alec

[PPV]

According to the Speedpro book written by Des Hammill on page 52 onwards it suggests that taking off 0.005" will usually be sufficient, that removal of 0.040" will give quite an increase to the CR for racing and that in total over the life of a cylinder head 0.060" can be removed and the cylinder head should still be sound.
This is a usefull book if you are doing any work on improving your engine as it covers the engine, carbs, ignition and exhaust systems. It is still available from various sources and the full title is 'How to power tune Jaguar XK 3.4, 3.8 & 4.2 litre engines'.

[bigcat1]

Thank you very much for these replies. I'm getting the head flatness checked out professionally shortly, so I'm hoping the result will just be a resurface. I might have a chat with the folks at SNG Barratts to see if they can shed anymore light on the composite gasket.
I shall have a go with the cams in place on their own to check they turn freely.
I hadn't bothered with that particular book as I assumed it was just about 'power tuning' which isn't my thing! But I think it might be a useful addition to my library. Knowledge is power as they say!