Call me crazy but I always thought all small block chevys used 11/32nds diameter valve stems.. Tonight I'm hand-lapping the valves in a buddy's chevy heads and went to NAPA to buy one replacement exhaust valve. I tell the guy I want a 1.50" valve for a...ohhh, let's say a 75 chevy 350.. [open chamber smog heads] He sells me one and I return home.stick it in the hole and its' super loose. I measured it with my vernier caliper and it is 11/32nds alright but it's too damn loose. I yank another [original] exhaust valve to find it's 23/64ths!. Whaat? Do I have heads with oversized valves or or are there certain years of SBC's with bigger valve stems? Signed: confused in the midwest.
Your heads were probably rebuilt by a large rebuilder like Jasper in their past. The rebuilder guys use +.003 thru +.008 valve stems so they don't have to mess with replacing guides. Just ream them out to next oversize and send them down the line. Only problem is Joe the homebuilder has no access to these valves. Or you have a pair of medium-heavy duty truck heads that use 3/8" stems. Common on all small blocks. Go to a real parts store and ask if they can call their warehouse and order oversize stem valves. Some manufacturers list them.
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