Join Date: Oct 2009
Location: far east north corner of Texas
So this is somewhat of an over simplification. If the Ford valves are 5.03's(not the only size around) and you get some 4.91 length valves(not the only size around) which are neither Ford or Chevy or actually they are Ford and Chevy for certain heads like AFR's then you are .12 short.
If you have the same cam and it wants the taller valve spring installed height, the biggest problem that causes is compressing the valve spring .12 more on the seat which increases the spring pressure and it reduces your total lift capability. Whether you get coil bind depends on how much lift your cam has. Regardless, it may work but it is technically wrong unless the valve spring installed height and the push rod length are corrected.
Depending on the heads, a shop might cut the valve pockets down to get the extra spring installed height but it would be best to get the right length valve for the specific heads and not have to cut on the heads. If you have a relatively high lift cam you might need a longer than stock valve to provide for the taller total lift. Regardless of which valve or what you are doing if any machine work has been done or you have swapped cams the push rod length needs to be checked and most likely it will be different that what it used to be.
Another valve dimension that could be different and something that has to be watched for is the valve stem width. AFR's for example seems to like 8mm valve stems for Ford or Chevy heads and in fact, advertise the exact same valves for their Ford and Chevy heads. However, Ford seemed to like 11/32nds(.3438) and so did Chevy for "the old stuff" but then there are some other valve stem widths also.
I'm glad I don't have to work on this stuff in a machine shop and I may have just made the water more muddy writing this. If so, my appologies. There are probably books just on valve train geometry, issues and solutions for all this.
65 2+2, 331, C4 presently apart for complete a restore
1979 Ford F150 custom, 302, C4, AC, tilt wheel, main transportation
Last edited by macstang; 06-30-2019 at 09:00 AM.