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-   -   Valve stem seals pontiac (http://www.hotrodders.com/forum/valve-stem-seals-pontiac-235106.html)

Nuck Chorris 07-19-2013 03:49 PM

Valve stem seals pontiac
 
Okay, I have been stunned. Took apart my heads and apparently the valve stem sealing is accomplished by an O ring and a bunch of grooves that are machined into the valve stem hole. Just did some research and found that installing positive seals or a bronze guide would require $machine work$. However, I am wondering, since GM designed it this way it must work, so how do I know if I need to replace anything or not?

Silver Surfer 07-19-2013 04:54 PM

You have to mill down the outer diameter of the valve guide boss to accept the positive valve seal. Also the new seal is going to require more clearance (the valve spring retainer will hit it). So for a low lift factory cam, maybe not a big deal. But with a higher lift aftermarket cam you might have to cut the valve guides for clearance. Either way you gotta check it. I believe Crane and Comp Cams make cutters for this and you can do it at home. But if it was me I would cough up the bucks and let the head shop do it.

MouseFink 07-19-2013 07:31 PM

Apparently a previous owner of those heads knurled the valve guides. That is a 10,000 mile repair of worn valve guides.

Take the heads to a competent machine shop and get a good valve job, have K-line phosphor-bronze valve guide liners and .530" I.D Viton rubber, metal clad, positive stop valve seals for 11/32" valve stems installed. Use Comp Cams 518-16 valve seals or equal.

Mr. P-Body 07-21-2013 10:36 AM

We use Pioneer OS-938. Viton "positive" seal. Same guide boss machining mousefink speaks of.

When the guide is replaced, often what's left of the original (a "shell" of iron about .020" thick) cracks or breaks off. This leaves no material for the original .535" size. For this, a .500" seal is called for. We use SBI 122-1275. It's also Viton, designed for the '82-'83 Ford 3.8 V6. Nice fit. Put them on all 16 valves. Delete the steel "splash shields" (dead weight).

We have also seen a significant number of "lined" guides fail due to the liner moving (in several engine families, including Pontiac). We don't use the process. We install true "thin-wall" guides (.502" OD). Avoid "spiraled" guides. For anything above .520" lift, bronze is called for (resists "side-loading" better than iron). There are some "hardened iron" guides available too, but we prefer the bronze. For under .520" lift, a stock replacement is fine.

While you're "in there" is the time to install screw-in rocker studs, too. It takes less work for the Pontiac than a Ford or Chevy small block. After the original studs are removed, the holes are perfect for 7/16-14 HeliCoils. No other machining is required, and you can utilize the stock pushrods, guideplates and bottleneck studs for a "non-adjustable" valve train if the cam has a stock base circle. HeliCoils are stronger than iron threads, so relax about that. It must be done on a precision machine, though (no hand-tapping).

Jim

MouseFink 07-21-2013 03:24 PM

The machinist that prepared my engine uses K-line Bronze Bullet, smooth wall, valve guide liners. The K-line phosphor-bronze thin-wall liners that were used on my 4.3L V6 Chevrolet heads have a maximum bored hole tolerance of 0.372" to 0.3735" I.D. with 0.530" I.D. Viton rubber valve guide seals. The Manley SS valves have 0.343" O.D. stems (not tapered) with .0015" intake and .0025" exhaust valve stem clearnce. My machinist uses the same K-line smooith wall guide liners on Pontiac heads.The name "Bronze Bullet" refers to the nose of the guide liner which is tapered so it will start in the bored guide hole easily.

It takes a experienced machinist with the proper K-line tools to correctly install and size K-line guide liners . It is not a job for a part-timer.

cobalt327 07-21-2013 05:25 PM

Quote:

Originally Posted by Nuck Chorris (Post 1695980)
Okay, I have been stunned. Took apart my heads and apparently the valve stem sealing is accomplished by an O ring and a bunch of grooves that are machined into the valve stem hole. Just did some research and found that installing positive seals or a bronze guide would require $machine work$. However, I am wondering, since GM designed it this way it must work, so how do I know if I need to replace anything or not?

The guides sound like they were knurled. That will mean the fix is a bronze liner in most cases. Machining for positive seals can be done at that time. Be sure that there's clearance between the underside of the spring retainer and the seal at max lift.

When GM designed the oil control for these heads there were less environmental concerns and the engines were basically low rpm, so the O-ring and tin splash shield arrangement was sufficient, if not ideal. Mainly it was cheap. Updating the seal arrangement to a positive seal and refurbishing the guides are what it takes to put things right. BUT- if you redo the guides, the seats will need to also be done because the center of the replacement guide doesn't always end up being in the same place as the original guide. Likely as not the seats are worn anyway, so plan on a 3-angle valve job to go w/the rest.

Question: What is the casting number of these heads and are they screw in or pressed studs? They should be screw in if original. That makes replacing the bottle neck studs a piece of cake. No helicoil, etc. needed, just remove old and replace w/new straight wall studs.

Nuck Chorris 07-22-2013 04:16 PM

just called around to various machine shops in my area. So it appears to me that I am going to be putting something like 350 minimum and they'll probably find more stuff that needs fixing. So I'm looking for a decent set of D ports off a 400 now, not going to put a bunch of money into fixing these heads.


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