Posted by Matt Wilson [172.71.174.252] on Sunday, November 05, 2023 at 17:42:46 :
In Reply to: Chris Case head thickness data posted by Kaegi [172.71.150.167] on Saturday, November 04, 2023 at 17:47:34 :
I know you weren't necessarily asking me, but I might have the info you need.
I have a 251 head that I believe was never machined till I had it milled. The engine it came from (early 60's Power Wagon) had standard cylinder bore diameters (not oversize) and standard crankshaft journal diameters (not undersize), so it had obviously not been rebuilt. It's always possible that the head could have been milled to correct a head gasket leak or something during its life, but if it was milled, it wasn't by much. I say that because I cc'd the combustion chambers before I had it milled, and the calculated compression ratio came out to exactly 7.2:1, which is the stated CR (in the manuals) for that engine in that year of Power Wagon. So all of that is to say I think it was stock thickness, or very close. The head has since been milled, and I told the shop to remove only what was needed to make it flat again. I wasn't looking to bump up the compression ratio for power. I think the shop removed 0.015" thickness, as "015" is stamped on the gasket surface of the head.
I went out to the garage just now and measured the thickness of the now-milled head in 10 places using a micrometer placed across the head gasket surface and the opposing bolt head mating surfaces on the top of the head. The numbers below are what I came up with.
1.9091
1.9102
1.9134
1.9123
1.8995
1.8996
1.9091
1.9100
1.9043
1.8992
The min thickness subtracted from the max thickness is about 0.014", so maybe that goes along with the 0.015" removed. If so, then I think the max thickness might be the figure that reflects something close to the original thickness. Everywhere else would have been machined more to remove warpage, resulting in those areas now being thinner than the less-milled areas. If that's the case, then 1.9134 is probably close to the stock thickness, possibly just a few thousandths less than stock.
Anyway, you have the numbers from my head, so you can use them in the way you think makes sense. I'd be interested to hear what your numbers are, if you don't mind.
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