Valve Stem Seals

[BadBrad]

Ok - so I put this thread in the nailhead area because my question involves a real old engine that I was working on this weekend, but (sorry guys) it was not a Buick. However it is pretty much a nailhead contemporary.

Engine is a '48 GMC 228" six banger. Is freshly rebuilt (about 400 miles on it) but pukes oil smoke on start up. Owner asked me to help check out/replace the valve stem seals. All we found on the stems was a tiny O-ring midway between the keeper and the guide. There is no way that this keeps oil from running down the guide and into the chamber. We replaced the O-ring with a standard umbrella type seal. Only did the intakes. Engine still pukes oil smoke on startup. Generally enough smoke to ground the luftwaffe, but only for a few seconds.

Question: Why didn't this fix the problem?

:Do No:

[Adam Whitman]

First, I'm gonna bet the guides were knurled, and not replaced. Second, when installing the O-rings, you have to put them on after the spring and retainer . Compress the spring and retainer assy, put on the O-ring, then the keepers. I don't remember exactly why this is but I do remember being told that if you don't, the thing won't work right. I think it either tears the o-ring or pushes it out of the right position. All the older SBC's used the o-ring, so it must work OK. Alot of guys used to use o-rings and umbrellas if they had a tired engine. I'd go umbrellas all around and see what it does for you.

[BadBrad]

Hey Adam. Thanks for the response.

Here are some follow ups.

Is the o-ring supposed to go into its own groove? (these valves only have a single groove for the keeper)

When you say "go umbrellas all around" do you mean umbrellas on the exhaust valves also? If so, won't the exhaust heat transmitted up the valve stem destroy the seal?

Again buddy, thanks for the help.

[Adam Whitman]

I think you'll be OK with the umbrellas on the exhaust valves too. You're right, they can get too hot, but I don't think that engine will ever do it. Yeah, I think the o-rings go into a groove of their own. Find an old Chevy servicve manual someplace and double check, or I'll call my dad(Chevrolet Master-Tech 66-78) and ask if you're in a pinch.