I'm replacing the valve seals in my 305 TPI. But I was expecting to see the umbrella type on both intake and exhaust. It has the o ring type on intake and exhaust, and the umbrella type on the intake only. Why not on the exhaust, the umbrella seals I purchased will fit the exhaust as well. On many other engines I've worked on , there were umbrella type on both.

 

Because they don't do hardly anything there, and the heat destryos them quickly anyway.

I've run more motors than I would care to admit to, with NO SEALS WHATSOEVER. All of them had NEW valves and guides, though. But if all of that fits tight, seals aren't all that necessary even on the intake.

 

Does that include no o-ring + shedder?

 

With no seals, doesn't it smoke?

 

Well its actually sort of mixed. Depending on what car the motor was destine for determined if it had seals on the intake and exhaust or just the intake. Typically heavier duty motors (like truck motors) got them on both. My understanding is that, while there not a bad thing to have on the exhaust valve, there's no vacuum in the exhaust port. On the intake valve the motor will tend to try and suck oil in past the valve guides but on the exhaust side there's higher pressures so if anything it would tend to push the oil back up into the motor. Now after the motors shut off and oil is allowed to sit in the head the game changes a bit but i hope that answers your question.

 

Due to the fact that when the exhaust valve is open, there is pressure pushing out, which means that it is pushing the oil out of the runner. This means there is no point in sealing the valve from oil seeping down.

Also the small bit of oil that seeps onto the valves help cool them.

However I will say that my heads now do not have seals on the exhaust and when I first start it after previously running it I get a puff of smoke. Probably from the oil seeping into the combustion Chambers.

Just what Rolling Thunder says ^

 

Right: no seals, and no smoke. No O-rings even. Not that those ever actually DO anything at all. And ESPECIALLY not with that stupid oil shield between the retainer and the spring. I don't think I've EVER put even ONE of those back in, if I took the retainer off, even on a stock motor. Just total dead weight IMO.

This is not with "reworked" heads with old junk stock valves; it is always with NEW valves, and NEW bronze guides, fit to .0015" MAX. Not over .002" for sure.

Not at all the same thing as taking an old wore-out set of stock heads, doing the cheeeepest thing to em you can legally call a "valve job", and forgetting to put them in. Which would typically smoke like a freight train.

I am in no way telling you to leave em out; only, that just because they're not there, doesn't automatically mean smoke. Use your own best judgment.

I prefer to cut the guides down to .530" or .500" and use Teflon seals when possible. No O-rings, no umbrellas, no splash shields.

 

My IROC smokes when I start it, and burns off after a running it a bit. I don't like it, but it's too much work (for not anyway) to put new seals on. I just let it smoke. Still runs great. Just gonna let it smoke for now. Doesn't seem to harm anything. I told my nosy neighbor lady I had it tuned that way for performance. She bought the bs.

 

Last cam change, I couldn't fit pos seals on all valves. Didn't want to pull heads to cut the guide bosses down, so I put the o-rings & shields on - just felt I should do something! I did ditch the rotators tho.

 

My BBC heads use triple valve springs which doesn't leave a lot of room for seals. After destroying a set of seals, I just leave them off now. I don't use seals on the intakes or exhaust but this also isn't a high mileage vehicle. Running alcohol fuel, the little bit of oil that travels past the stem actually helps as the alcohol is so dry.

As mentioned above, seals on the exhaust valves are not required. There's always a slight possibility of oil leaking past the valve when the engine is off which could cause a slight puff of smoke when the engine is started if it drips past the open valve and into the cylinder. When the engine is running, there's zero chance of oil getting into the cylinder past the exhaust valve. The intake valve however is open as the piston is pulling in the air/fuel mixture and could pull oil past the valve stem so the intakes do need seals.

 

I've run them both ways. On one set of heads I actually did a back-to-back test with and without exhaust seals. (And the seals I was using were a late model set of Viton seals, like Vortec heads use). They didn't seem to make much difference in the little puff of smoke at startup or any other time. Didn't have enough drive-time to say what the long term oil consumption difference would have been, though.

Then I tried the intake side.... Without intake seals the puff was noticably larger, especially after letting the engine sit a while. I'm sure the long term oil consumption would have been higher, but no data to prove it.

The heads were a low mileage set of Iron Eagles, but definitely not new and I'm sure the guides had a smidge of play in them. My conclusions were along the same lines as was posted by others, above. The exhaust side runs hotter and isn't under vacuum so the seal is probably less of an issue on that side.

 

Are you saying that a little oil in the combustion chamber acts as a top cylinder lube?

 

Only if the guides are worn but some oil down the valve guide is better than none in an alcohol engine. Since I started running alcohol and not using valve seals, I've never seen that "puff of blue smoke" when I've started the engine and it sits longer than a street car.

 

Seems to me that no seals on the exhaust guide might contribute to blow by, if the guides are worn or at their service limit.
My engine does have a puff of blue smoke on cold start up, and the main reason I'm replacing them is cause I failed my emission test. My CO and HC are almost double the acceptable limit. I will be replacing the O2 sensor and the Cat after I've replaced the seals.
The valve seals on the intake side are definitely worn and are most likely part of the blue smoke on cold start up. I will install them on the exhaust side as well to hopefully help stop the smoke on start up. Not that seals on the exhaust valve contribute to high CO an HC's.

 

I would bet burning oil would ruin a cat. I read somewhere that when you have the valve covers off, clean the oil drain holes on the heads so oil will drain back into the pan faster. The oil has less time to seep into the guides.

 

 

I'll go ahead and show my ignorance here, but since it's been 6+ years since I built my 350, my memory is a bit hazy.
What's a rotator, vs an umbrella shield, vs a splash shield? I use positive seals, and I can picture what I think is the "splash shield", but now i'm wondering what the umbrella shield looks like??
If anyone has a picture, i'd be forever indebted to see the difference.

 

Rotator is a device under the exhaust valve that rotates the valve as it moves up and down. I can't remember if some vehicles use a rotator as part of the spring retainer on top or not.

An umbrella shield is a cap that fits over the valve spring to keep the oil spray contained over the spring itself which helps cooling. This is also probably referred to as a splash shield.

Your positive seals are just valve seals that clip onto the valve guide to provide a tighter seal. OEM valve seals are just a square oil ring that fits over the valve stem. They dry out from the heat and crack or break after a few years.

 

Ok, thanks Alky, that's about what I thought then.

 

There are also the umbrella seals, which attach to the valve stem and ride up & down with the valve. I'm using a mix of positive and umbrella seals, together with the o-rings and umbrella/splash shields (for what they're worth).