hogwild4

I have a 1977 C3 with a stock 350 SBC. When it’s first started after sitting for the night it runs like it’s on 6 or 7 cylinders and does put a lot of smoke out the exhaust. After a few minutes (2-3 minutes) the oil (I assume) burns out of the cylinders and the engines begins to run as it should. For the rest of the day the car will start and run nicely with little to no smoke from the exhaust.

This car had sat with very few miles being put on it for 15 years so I suspected bad valve stem seals. With some assistance from a Fel-pro technical rep, I purchased new O-rings and conventional rubber umbrella stem seals. During the dis-assembly I found that the existing O-rings were shot and there was no sign of umbrella seals even existed! I don’t think umbrella seals were ever in it. Most of the O-ring seals were basically crumbs, a few completely gone and a few there but very brittle.

I installed the new 0-rings and rubber umbrella seals and believe the work went properly. However the car still has the initial start, fouling issue. It’s better than before the new seals but none the less still a nasty fouling at first.

I understand this is a poor man’s valve job but still I would have expected better results!

Do we think if I change the conventional rubber umbrella seals which move up and down with the valve to the positive stem seal type that stay fixed on the boss it will made a big difference?

derekderek

You should replace the 40 year old valve springs while you are in there. Plus you can ditch the metal umbrella cups and valve rotators that are just unnecessary valvetrain weight. Mebbe consider beehives. While springs are off, wiggle the valve stems and see if any 1 or 2 are looser than the rest. A lighter valvetrain acts like a much heavier spring high perf valvetrain without the spring loads that could eat the 40 year old cam. You want about 80-100 lbs seat pressure tops with a stock cam.

HeadsU.P.

No need for new springs. The "fresh" additional pressure would just put more strain on some old lifters & lobes.

The way you did the seals is fine. Not like you're going racing and you learn to live with a puff of smoke at start up. That's just part of having a tired engine. If mine didn't smoke at start-up, I would wonder if I had oil pressure topside.

I never cared too much for those cheap GM rubber umbrellas. They got hot, worn, crumbled way too soon. Just my opinion, but I think Comp Cams blue umbrella seals are better at $25 a set. They have a little metal "O" ring the rides the valvestem and the better quality to go the distance. But too late now, you're sure not going to tear that valvetrain apart again.
Its fine. Drive it.

hogwild4

Thanks for the thoughts HeadsU.P. Actually I'm not concerned with the smoke at start-up so much but the foiling of the plugs for the first few minutes is what gets me. It wouldn't bother me at all to tear the valve train down again (I'm retired) to install better seals if I were confident in getting the right seals and there was hope they would improve the start-up oil fouling situation. Problem I see right now is that I'm not finding a positive stop seal to fit without having to machine the valve stem bosses. I mic'ed the valve stems and their 0.341" and the valve stem bosses are 0.562". The valve stem diameter is common enough but it's the boss 0.562" dimension that I can't seem to find on the positive stop seals.

HeadsU.P.

There is no rhyme nor reason to machine the bosses on a stock engine at this time. If it were mine, I would just let it go until the time is right for pulling the heads and doing the full premium expensive, timely job.

But for now, do you ever use the Summit search feature? See what they have for stem seals w/o machining.

jackson

OP
it's likely yours has worn guides/stems.
seems your new double band-aids didn't cure it.
Now's the time to decide options
Do nothing & observe things worsen
pull heads and have machine shop service them (overhaul)
replace heads with like kind
replace heads with upgrade
pull motor and overhaul motor
pull motor & replace with upgrade.

it's your car & money. New Seals only go so far & you now know that.

-edit-
posi seals cannot hold back oil being sucked thru guides when valves wobble because worn stems and/or guides.

jackson

OP
This fellow bnr517 is considering swapping heads on his zz4 to trickflow heads...………. zz4 heads would be good swap for yours.

maybe he'll sell you his zz4 heads?

his post # 16

https://www.corvetteforum.com/forums...post1598913212