[25stevem]

While helping a friend out last night with a question as to what’s safe to mill off a 6X head I finally wanted to see what there was for stock Deck thickness as best as I could without sectioning up my Mule head.

This is what I found.
This thickness of .219” is about 1/4” in from the water holes and then it tapers down to about half that at the perimeter of the passages.

This shows two things, 1) I would say that a mill on a stock uncut head of .060” which will leave you about .160” is safe and 2) but even in stock form and to better guarantee against no cracks I would take the time to roll over all the edges of the passages in the Deck since they taper down from .219” so much.

Note that your results may veri since my Mule head came off a motor with only 30K on it and was always run with the proper antifreeze mix.