350 valve seals

[prodjay10]

Which valves seals are needed for this truck? I believe it's completely stock.

Not sure if umbrella or positive type is needed.

1972 gmc w/ 350cid.

[tdangle]

I recently replaced all of mine with the umbrella type. Not very expensive, I got mine from NAPA. I did mine with the heads on in the truck. Next time I'll spring for a better spring compressor. The Autozone loan tool one sucks.

[mattfranklin]

As far as I know, stock had the umbrella seals. But two out of the three sets of heads I have had were already converted over to the positive stem seals.

There are tradeoffs. Stock is simple, easy to install, leaks a little, and possibly has less guide wear. Positive seals make more room for things like double valve springs, but take extra machining to install, control the leakage better, but might wear a little faster.

I've had two different machinists whose opinions I highly trust tell me that they prefer the opposite things. But the one who preferred the positive stem seals also made sure I had quality hard chromed valve stems and machined it for new hardened "false guides." I'm an engineer and can see plusses and minuses of both schools of thought.

Remember to install the splash shields and o-rings on the valve stems if you decide to go that way with stock umbrella seals .

If you want to do the positive seals, and you trust yourself, Comp Cams has a tool for about $50 to machine down the tops of the valve guides to accept the positive seals. I've gotten myself into trouble before with one of the Comp spring seat tools, but I'd trust myself (I think?) with the valve stem tool.

Good luck in whatever you decide.

[GRX]

That era will have neither. If stock that is. They used o-rings which work in conjunction with retainer and shield to act as a big umbrella.