How much can you skim a twin cam cylinder head

[rgh0]

In response to a question about this I have attached a photo of a spare head of mine.

It is 4.540 inches thick - 60 thou less than a big valve at 4.600 inches and 100 less than a standard head at 4.640 inches. It is perfectly usable and has served as a reliable race head for many years at that thickness. I have seen heads used down at around 4.520 inches thickness without issue.

You will see in this head photo that the cast lettering has just started to have the tops taken off at 4.540 inches. At 4.520 inches that lettering is almost gone !!!

The real limit is the water jacket under the exhaust port. If you skim to far you will break through into that, you need to thickness test in that area if you are going to skim down around the 4.52 thickness to check as its location is variable depending on how the cores were set originally for the casting - but even then you can always weld it up if you break through.

so don't be too worried about how thin a head is !!- hardness and corrosion are the real killers of heads as fixing these issues is generally not economic.
cheers
Rohan.