valve stem sealing options

[robert leazenby]

I am ready to reassemble my 70 LT-1 heads and having a dilema trying to figure out the best combination of O rings, guide mounted seals, and splash shields. It seems there are many schools of thoughts.

I am leaning toward either of the following:

O rings on both intake and exhaust, current Chevrolet guide mounted high temp rubber seals on the intake only, and spash shields installed on both.

Some sources suggest not installing splash shields on high performance engines, but install them on stock engines. One source for my dilema is deciding where my engine falls. Though now built at stock specs, it is an LT-1 (stock or high performance?)

I have replaced the heads with new GM performance 492s (not cheap) which are induction hardened on the exhaust seats. Valves are stock 2.02/1.60. Springs are new stock 80 pounders (single with dampners). New GM HD push rods.

The heads are going to be installed on the original block and in six months will be installed a newly built short block which will be to 70 LT-1 specs.

Any suggestions with explanations would help me make the decision

[Joe L.]

Re: valve stem sealing options

robert-----

Your best bet is exactly the option that you mention------use stock o-rings on all valves, stock, late model Viton positive seals on the intake valves, and maintain the stamped steel, cup-shaped seals on ALL valves.

By the way, the current GM casting #3991492 cylinder heads (GM PART #12480092) do not have induction-hardened exhaust valve seats.

[robert leazenby]

Re: induction hardening

It was my understanding when I ordered the heads that they would not have the induction hardening. When we opened the box yesterday, there was most definite discoloring on and around the exhaust seats normally associated with induction hardening.

Thinking they got me the wrong heads, we double checked the cast #s and part numbers. I even referenced the performance catalog for them to show that they should not be hardended. The parts guy was confused as was I.

Finally I took them to my head guy, who also stated that they had been hardened.

I guess we could be mis-reading the coloring around the exhause seats. Do you know what else that it could be?

[Roger Legge]

Re: induction hardening

Devil's advocate here. I wonder if the intake guides would get sufficient lube if using both o-rings and positive seals. Just a thought.

Roger
#36316

[Duke W.]

Re: induction hardening

Good question, but the answer is also a function of the valve guide material.

I don't have the specifics, but guides and seals should be choosen as a system. The seal needs to pass an amount of oil that is suitable for the guide material. Most modern engines that used nickel-bronze guides use "positive" type stem seals.

duke

[Joe L.]

Re: induction hardening

Duke-----

The valve guide sealing system that I described (o-rings, Viton seals on intake valves, and stamped steel caps) was actually used by GM on most 81+ small blocks. About 1992 for LT1s they did go to different positive seals, though.

[Joe L.]

Re: induction hardening

robert----

What you describe sounds like induction hardening. However, GM says that these heads do not have induction hardened seats.

Part of the reason for this, I think, is that the induction hardening, for small blocks, was usually done only on heads with exhaust valve seats that were specially configured. These heads have a slightly raised, cast "boss" around the valve seat. This is necessary to prevent cracking of the seats and provide extra "insulation" between the induction hardened material and the native cast iron.

GM must have started doing it on castings which were not originally designed for it.