Thurman_Merman

I put a new cam in and everything is great besides it smoking from the exhaust very badly. It turns out that even though I have plenty of clearance to run .500+ lift the lower ridge on the valve stem dips below the seal and has deformed it to not sealing at all. I have fixed body positive type Viton seals in there now, is there another type of seal that is lower profile that would work for me? Machining off the bottom of the fixed body seal to make it fit lower on the boss maybe? I really don't want to replace the valves, or change the camshaft again. I searched for almost an hour on the subject and haven't found much. Thanks for the help.

Thurman_Merman

I called alexsparts and apparently I have old style valves with two grooves that were put in by whoever rebuilt my engine. The correct repair is to pull the heads and put in the correct valves or machine the guide bosses down. I'm going to try to modify new seals before I pull the heads. I doubt anyone else will have this problem but I'll post the results anyway.

Tuned Performance

iTrader: (92)

Just curious what factory heads that you have .500 +.060 clearance for the guide to locks ?
I thought the two groves the top is for a o-ring to keep oil on the valve stem and the retainer goes into the lower groove. Sounds like the keeper is cutting the seal. Comp cams sells the cutters a lot of sbc cut to .530 on the guide. Another solution since its that close is to get offset .050 keepers.
http://m.summitracing.com/parts/CRO-86107X1-16/
http://www.alexsparts.com/locks-keep...er-060-higher/

Tuned Performance

iTrader: (92)

Scratch that, those offset the keeper for sling instal height.

AlkyIROC

So many people don't realize that there are so many other clearances for a cam swap other than piston to valve.

Coil bind
The underside of the retainer hitting the valve seal at max lift
The slot in the factory stamped steel rocker hitting the rocker stud at max lift
Valve train geometry

If your heads have not been modified for the extra lift required then you are normally going to have at least one of these issues.

The most common repair for the valve seal contact is to have the tops of the valve guides machines down for the extra clearance. The alternative is a longer valve with heavier springs to keep the same spring rate at the higher installed height. +0.050" keepers may also help but will also change the spring's install height meaning less spring tension on the valve which could also cause valve float.

The dual groove valve stems are factory stems. The keepers sit in the upper groove and a valve seal square o-ring sits in the lower groove. For many years this was what GM used for valve seals with a simple umbrella seal on the intake valves. Exhaust valves don't need much of a seal and the ring on the stem was enough. Your positive lock seals are too big. Without doing a lot of work to fix the problem, put the factory umbrella seals on instead.

Thurman_Merman

The heads I have are factory alum 113/zz4 heads, I know they have been re worked but I don't know to what extent. I actually have .600+ from the retainer to the guide boss with no seal, but I have shorter aftermarket retainers. The retainers are fine but about the guides, they have a factory .558 diameter but I don't know of they have been cut shorter. From what I understand the valves for a 91 should only have one groove for the retainer locks, the second groove was for an o-ring/ umbrella type seal that discontinued in the 80s. Since my aftermarket retainer is so short it won't extend far enough to hold an o-ring type seal. The problem I'm having is a newer seal configuration vs. an older valve configuration.

Thurman_Merman

I don't think you quite understand my problem. Coil bind: fine. Valve seal clearance: fine. Retainer and spring installed height: fine. Rocker clearance for max lift: fine.

As I said in my last reply I think I have older valves in my heads and the lower groove of the valves is interfering with my modern seal. My factory retainer hit the seal at under .500 and onwhen I switched to an aftermarket retainer the lower groove became exposed, hence my problem. With the lower groove exposed I must use a positive seal because the o-ring cannot install properly.

Without replacing the valves I think working a set of seals is my only option, if you have another idea that doesn't involve machining the guides I'd love to hear it.

AlkyIROC

Sounds like you need proper valves then.

My race engine doesn't have that problem. Triple springs doesn't leave a lot of room inside. Since it's not built to be a high mileage engine, I don't run valve seals. By the time my guides get worn enough to cause leaks, the heads will need to be rebuilt.