Valve Stem Seals

[bishir]

I have a pair of stock heads I'm having ported and polished at the moment. Should I have new seals put on the exhaust side at the very least? If so where do you buy them, and what is involved? I just want to know beforehand when dealing with a machine shop.

BTW, does anyone know the reason our exhaust valves do not have these from the factory?

 

[TurboDave]

If you notice the exhaust valve stems have a "cutout" on them. AND the exhaust valve guides are taller than the intakes. For these two reasons you cannot put seals on the exhaust valves.

I you absolutely insist on seals for the ex side, then you'll have to get the guides machined down shorter, and cut for seals, and you'll need smooth stem ex. valves to replace the ones you have.

Way too much trouble for no gain.

 

[bishir]

If you notice the exhaust valve stems have a "cutout" on them. AND the exhaust valve guides are taller than the intakes. For these two reasons you cannot put seals on the exhaust valves.

I you absolutely insist on seals for the ex side, then you'll have to get the guides machined down shorter, and cut for seals, and you'll need smooth stem ex. valves to replace the ones you have.

Way too much trouble for no gain.

I don't insist because I didn't have a problem with not having them... someone suggested it as an upgrade in another thread and I was curious as to why our cars didnt' come with them. I'm glad to hear there isn't much to gain from this, and I plan on leaving them alone. Thanks for your reply!

 

[kidglok]

I don't insist because I didn't have a problem with not having them... someone suggested it as an upgrade in another thread and I was curious as to why our cars didnt' come with them. I'm glad to hear there isn't much to gain from this, and I plan on leaving them alone. Thanks for your reply!

Champion irons have exhaust valve seals, could be what they were referring to?

 

[earlbrown]

Normally exasperated cars have a negative pressure pulse on the exhaust port when the valve is closed. That will draw oil down the valve guide and burn it in the exhaust system. Since we have pressurized exhaust, that's not a factor.

 

[bishir]

Normally exasperated cars.

Normally I'm the one who's "exasperated." Thanks for your reply... that's what I was wondering and it makes sense.

 

[Steve V]

I have to respectfully disagree. TTA's have seals on the exhaust.

When I did Turbopete's rebuild it smoked at idle from the word go. After I ruled out the turbo, off came the heads and back to my machine shop they went. he gave me an ARTA (?) buletin that said to machine the guides swap valves and install seals. So we did problem was fixed. He said valve guides were well within specs also.

My personal GN has no seals and will start to smoke at idle, have not ruled out the turbo ( was new when installed) but eitherway, it will get seals eventually. I have done sveral engines since Pete's and they all get this upgrade and none smoke. It is cheap.

Sorry to go against the heard on this one :0)

 

[bishir]

Sorry to go against the heard on this one :0)

Respectfull discourse is always appreciated on my end. I'm familarizing myself with the topic and respect both opinions.

 

[earlbrown]

I have to respectfully disagree. TTA's have seals on the exhaust.

When I did Turbopete's rebuild it smoked at idle from the word go. After I ruled out the turbo, off came the heads and back to my machine shop they went. he gave me an ARTA (?) buletin that said to machine the guides swap valves and install seals. So we did problem was fixed. He said valve guides were well within specs also.

My personal GN has no seals and will start to smoke at idle, have not ruled out the turbo ( was new when installed) but eitherway, it will get seals eventually. I have done sveral engines since Pete's and they all get this upgrade and none smoke. It is cheap.

Sorry to go against the heard on this one :0)

 

[earlbrown]

Do TTA's have stepped stems on the exhaust valves? When the bulletin said to swap valves you need to run seals if they aren't stepped.

If you run an unstepped valve with no seals and proper ex guide clearance I would expect it to smoke at idle.

 

[ek02]

The main reason to cut the exhaust guides, use smooth stem valves and valve seals, is to give enough clearance between the retainer and the seal if you use a cam with higher lift than stock. If you cut the exhaust guides for clearance and dont use seals, it will smoke like crazy at idle. I tried it once and had to pull the heads off and do it right. With a stock cam, you can leave the exhaust guides and valves alone and not run a seal. If you are having the heads ported, have the guides cut, seals installed, and new exhaust valves with smooth stems installed. Then you are all set if you want to swap the cam later.

 

[Steve V]

Do TTA's have stepped stems on the exhaust valves? When the bulletin said to swap valves you need to run seals if they aren't stepped.

If you run an unstepped valve with no seals and proper ex guide clearance I would expect it to smoke at idle.

Yes TTA valves are smooth stems. Do you have a copy of that bulletin? I may at home in my stash of papers.

 

[Steve V]

The main reason to cut the exhaust guides, use smooth stem valves and valve seals, is to give enough clearance between the retainer and the seal if you use a cam with higher lift than stock. If you cut the exhaust guides for clearance and dont use seals, it will smoke like crazy at idle. I tried it once and had to pull the heads off and do it right. With a stock cam, you can leave the exhaust guides and valves alone and not run a seal. If you are having the heads ported, have the guides cut, seals installed, and new exhaust valves with smooth stems installed. Then you are all set if you want to swap the cam later.

Yes that is another reason to cut the guides. Hopefully anyone would be smart enough not to try smooth stems without a positive seal.

I have ran stock heads, stock type low lift cam with factory valves/guides and smoked at idle. The fix was smooth stem valves, cut guides, positive seals.

 

[bishir]

I plan on running a mild cam, at what point are you looking at needing added clearance?

 

[Steve V]

I plan on running a mild cam, at what point are you looking at needing added clearance?

Need cam specs to be sure, there was a thread recently where someone actually measured it.

 

[ek02]

An old Kenne Bell catalog I have says that any cam over .420 lift at the valve needs the guides cut on 83 and older engines. The 84-87 heads can take a cam with .460 lift at the valve without cutting the guides.

 

[earlbrown]

That catalog also said that every part they sold was worth .2 and 2MPH's.


It's easy enough to check. All you need is a dial indicator and a magnetic base.

 

[turbofabricator]

That catalog also said that every part they sold was worth .2 and 2MPH's.


It's easy enough to check. All you need is a dial indicator and a magnetic base.

Hahahahaha...... Funny Earl. I've been critical of them since 1988. If you bought everything from their catalogue you would have beaten John Force! I'm glad to see that the valve stem issue is now know by many folks. I have discussed this issue many many times on this and other forums since the early '90's.

 

[Paul Lohr]

Normally exasperated cars have a negative pressure pulse on the exhaust port when the valve is closed. That will draw oil down the valve guide and burn it in the exhaust system. Since we have pressurized exhaust, that's not a factor.

Is it safe to say that turbo engines have exhaust pressure on the bottom of the exhaust valve guide for some period of time? Isn't that pressure attempting to squeeze between the exhaust valve guide and exhaust valve stem to find its way into the valve cover area?

 

[earlbrown]

Is it safe to say that turbo engines have exhaust pressure on the bottom of the exhaust valve guide for some period of time? Isn't that pressure attempting to squeeze between the exhaust valve guide and exhaust valve stem to find its way into the valve cover area?

It's exactly like that. If you ever dissemble a head that had a restrictive exhaust and/or a lot of miles, you can see black burn marks all the way up the valve stem.

On our cars if you have a 2:1 pressure ratio, for example, on the turbo and run 15#s of boost, you have 30PSIG in the manifolds on average (with serious pressure spikes every other TDC). 3:1 would be 45PSIG at the same boost level. The stem to guide clearance is exposed to that pressure.