Re: Low compression

Posted by Ross On 2014/5/2 20:27:53

This cylinder head question comes up over and over so I did a little research in the inventory:

I wandered through the magic basement and measured every cylinder head I could find that I was reasonably sure had never been milled. They ALL measured 1.781" thick, or if you prefer 1/32 over 1 3/4. These were all 48-54. So that seems to be the stock thickness. The 359 heads are another matter, and I didn't have any to measure.

Further, it turns out there is an easy way to tell if they have been milled. All the untouched heads showed broach marks; that is they were not cut flat with a rotary cutter, but were rather dragged under a highly glorified file to flatten them. This can be seen by the longitudinal scratches from this process. If milled, you will probably see circular marks.

And about milling heads to "true them up". I only do it if there is erosion or other damage. These heads are actually quite flexible. I supported a head by its ends on my Bridgeport's table and placed an indicator in the middle. I can flex the head .002 with my fingers. Those 38 nuts are going to pull out any reasonable amount of warpage.