14/10/2026
Advice needed: valve stem seals for early SBC heads
I’m rebuilding a 283 with early small-block Chevy heads marked 3795896. The machine shop measured:
* Valve stem: 8.65 mm
* Valve guide OD: 14.50 mm (about .571 in)
They say these heads need a full, guide-mounted positive valve seal—not just the valve stem O-rings. The seals I bought from Summit, Enginetech EGN-S2926-20, are too small for the guides (0.500”). The seals supplied with my COMP cam kit are O-rings only.
The cam is a COMP K12-234-2, with .447/.454-inch lift. Has anyone fitted positive seals to heads like these? I’d really appreciate the part number and supplier you used, and whether the guides had to be machined or lowered to get proper retainer clearance.