Re: 1951 288 Packard Valve Clearance Notes: What is the minimal clearance?

Posted by HH56 On 2024/6/4 13:57:26

I cannot answer your question either and Don is correct that Packard did not give clearance specs. Aside from valve sizes and open/close timing the only other spec they shared was valve lift which for 51 was .342 on all engines.

Somewhere on the forum the original post for this head thickness info will be found. In 2014 a post was made regarding measured head thickness. Silly me saved the info but neglected to note who the author was. From the way it is written and the magic basement reference I suspect it was Ross but if not I hope the actual author will claim credit again..

You might be able to take a look at your head and see what is mentioned regarding broach marks on unmilled heads. If not perhaps you can measure your head and possibly get a good feel if it has already been milled and doing it once more might be too much. If you have already lost thickness I would be extremely careful on having any more milling done. You can also do the clay test which may be mentioned in the earlier post of a week or so ago that Don referenced. That test will give you a fair estimate of how much actual clearance you are dealing with.


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 it 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.