The Stovebolt Site Forums The Shop Area Engine Shop Valve Seals

Do you recommend putting modern Viton valve seals on both intake & exhaust valves on older GMC/Chevy inline 6 cylinder engines?

I'm working on a pair of GMC 270's and I can get 11/32 x .562 Viton seals, but wasn't sure if putting them on all 12 valves was a good idea.

I use the positive seals with the garter spring only on intake valves. Exhaust valve guides don't have vacuum against the bottom of them, so they can either use the floating umbrella seals or the O rings under the retainers- - - - -either/or NOT BOTH! I just opened up an engine with too much oil sealing, and totally worn out valve guides.
Jerry

Just curious, how come these old engines won't work the best with viton seals on all 12 valves? Granted the oldest engine I've rebuilt is a Tempest four, half a 389, but it had viton seals on all valves and was great. I miss that car.

I would strongly discourage the use of positive valve stem seals at all for a 39-62 Chevrolet engine. They work too well for keeping oil away from the guides.
There apparently is not enough oil moving around under the valve covers on these engines to get past the positive seals to lube the valve guides and they wear out fast.
I learned this the hard way.
The machine shop talked me into them. I should not have listened.

Mostly it's because there is a fairly low volume of oil available on the top end of stovebolt engines, particularly the early ones with less than full oil pressure in the rocker am shafts.
Jerry

Ahh, that makes sense. The Pontiac V8s have a huge oil galley under the drilled rocker arm studs, so there's just all kinds of oil up top on those engines.

I have a booklet about that four, written by the guys who designed and built it, and presented at the Autorama in November 1960. It goes into some detail about how proud they were of the extensive ball and socket rocker arm lubrication setup they had made for Pontiac engines.

I could totally see why GMC used a variant of that V8 in their trucks. IMHO they should have continued with it versus the 366/427 industrial engines-every one of those I found in the salvage yards back in the '90s had spun bearings and other issues, yet were still ludicrously expensive because 'Big Block Chevy.' No small part of why I went to the Cadillac V8 with its burly bottom end. And yard full of free cores I had to hand.. :-D

I had an 848 head rebuilt with bronze guides and lip-type seals. They were set up with about 0.0015 clearance. I had one exh valve hang up and the engine started missing. I shut it down and let it cool then gave the adjustable main jet an additional 1/4 turn out. Problem solved. This was a cool, dry morning below sea level in AZ. They seem just fine 30,000 miles later.

I run them on both valves as I have since at least the early to mid 1980s. I have always run them in conjunction with bronze valve guide liners and I am very particular as to making sure there is a little clearance. The guides need a little oil so sometimes I have to polish the vale stem a bit to get the the right feel. All these years, never a problem.