[Firebob]

I pulled the intake yesterday and can see down to the backside of the intake valves. I got some oil build up on the flat area. I was able to scrape a bit off with a screwdriver and it's really gooey. Almost like some kind of soft rubber but I assume it's oil that got past the seals and made it's way down the stem onto the valve. I'm going to pull the heads and clean things up. I'll have to wait to see the exh valves but I suspect the same. While I have it opened up I will replace the seals with some new ones.
Anybody got a link to a good set of seals?

[steve25]

First need to know if the guide (s) is cut for .530" , or .500" seals!

[HWYSTR455]

Also need to be sure the height is correct if it's cut for PC seals. If not, it's very likely the retainer will contact the seal and destroy it.

There is a certain amount of leak past the seal which is a good thing, it lubricates the guide, so need to determine if it's excessive or not. Can probably tell by inspecting the seals and guide clearances.

Fuel too can leave deposits on the valve stem, and if it's running rich it can be excessive. Think of the heated valve stem and cooler fuel passing over the stem, and you will get the picture of how that can happen.

There's always going to be some build up is my understanding. Did the heads have guides done? How many miles on them?

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[Firebob]

Don't know how many miles on them. I'll have the guides checked too while they're off. What's normal clearance for stem to guide ID? I'll have to measure the guides but it seems like they were .500, IIRC. I'll post a pic of the bare guide. Maybe someone can see if they have been cut for PC seals or not.

[mgarblik]

Typical stem to guide clearance is .0015-.002 on the intake, .002-.0025 on the exhaust. If the intakes exceed .003, you will get some smoke and oil use in high vacuum conditions. Exhaust can go to .0035 before you have real issues. As far as seal cut dimensions, both .500 and .530 are very popular. Simple caliper measurement will get you close enough. With the valve in it's full open position, I like at least .060" from bottom of retainer to top of seal. If someone has gone to the trouble of cutting for seals, they probably have that right. But check to make sure.

[Squidward]

Originally Posted by mgarblik

Typical stem to guide clearance is .0015-.002 on the intake, .002-.0025 on the exhaust. If the intakes exceed .003, you will get some smoke and oil use in high vacuum conditions. Exhaust can go to .0035 before you have real issues. As far as seal cut dimensions, both .500 and .530 are very popular. Simple caliper measurement will get you close enough. With the valve in it's full open position, I like at least .060" from bottom of retainer to top of seal. If someone has gone to the trouble of cutting for seals, they probably have that right. But check to make sure.

Like you said, check. I have a pair of heads that were cut for .500 seals, but they were only cut down to the tops of the stock guides before I got them. With the extra added height of the seal on top of the guide, the total allowable valve lift was barely .420 at best. And it had evidence that it was getting some crush from the valve retainer.

[Firebob]

Top of the guides measure .530. Can you tell from the pic if they've been cut for PC seals or not?

[Firebob]

Another of the grunge on the backside of the intake. That stuff is really baked on there.

[steve25]

Oh, you have aftermarket heads! Yes those guides are ready to go for seals!

[HWYSTR455]

That looks like a retainer contact pattern on the top of that seal of the valve that has gunk on it. To me, it looks like that guide needs to be cut down to prevent retainer contact.


EDIT: Also looks like the spring locator is an inside type, and you may not be able to move the seal down any further (by cutting the guide down). Looks like you need to go to an outside type spring retainer to allow the seal to go down further, or go to longer valves. If longer valves, you will have to recheck your pushrod lengths.

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[Firebob]

Anybody have a link to a set of good valve seals to use? PC? Viton?
That ring you see on top of the black seal is just a design in the part. I thought so at first but when I wiped them off I could see that's just what they were supposed to look like. The blue one that I had on the exhaust valve seems like a more substantial material. Only a bit of carbon buildup on the bottom part of the exhaust valve( like you expect) so I think those are good to go but I'll just replace them all while I'm at it.

[Firebob]

Ok so it looks like the seals are listed for .344 stems. Mine measure .341( like they are supposed to). What gives? .003 seems important when they are supposed to seal against oil. Especially since the result of them being too loose is what I'm trying to avoid again.