Don Terrill’s Speed-Talk

ZZ4/L98 heads, OE PM guides, chrome stem PEP valves. Currently has 1.25" springs and OE-type PC seals on intake and plain umbrellas on exhaust, working well like this for many years.

Changing to dual springs with a .700" inner and need smaller OD seals to suit. I found LT1 seals are the same dimensions - .562" guide 11/32 stem, so picked up a set of Enginetech S9210's for it. These are sure to be fine on the intakes but I'm skeered of upsetting things on the exhaust side.

What should I do? No seals at all on the exhaust? Use the Vitons and stop worrying? Try to find some sub-.700" umbrellas (not had any luck with that so far)?

One old trick is to pull the spring off the top of the valve seal on the exhaust side.

But... is that the solution, or just another option to add even more uncertainty into the mix? I want fewer options!

turbo camino wrote: ↑Mon Nov 11, 2019 3:08 pm But... is that the solution, or just another option to add even more uncertainty into the mix? I want fewer options!

I don't know, thats how I have always done mine with no issues.

turbo camino wrote: ↑Mon Nov 11, 2019 1:59 pm I found LT1 seals are the same dimensions

On LT1's and L31's etc from that era....these engines have a different intake and exhaust valve stem seal. The aftermarket tends to just sell 16 of the same intake seal. I like to use the GM seals in applications where the guide diameter allows. GM part# 10212810 for the intake(black in color), GM part#12564852 for the exhaust(orange in color)...lighter tension spring on it.

They are sold individually and the price kind of adds up. I've used that orange lower tension exhaust seal quite a few times...on intake and exhaust.

I've also pulled the springs off the exhaust seals as well, like previously mentioned. ..but that was mostly on the Teflon pc seals.

This is what I have: https://www.rockauto.com/en/moreinfo.php?pk=5571951

On the #12564852, I see some places have it listed as for 5/16" stem, assuming that's an error. Is it a different material or is the oil metering different and the orange just for identification? Sheesh, I thought Viton was Viton...

turbo camino wrote: ↑Mon Nov 11, 2019 4:14 pm Is it a different material or is the oil metering different and the orange just for identification?

That's possible, but I recall it having less tension. The interesting thing is, that even in the GMPP catalog. Gm just calls out the use of 16 of the 10212810 seals for use on both intake and exhaust on the performance heads. Yet the catalog shows separate intake and exhaust seals for the OE applications.

I think I'll try it with no seals on exhaust. If it doesn't work it won't break anything, I can add seals later if it's a problem.

CGT wrote: ↑Mon Nov 11, 2019 3:33 pm

turbo camino wrote: ↑Mon Nov 11, 2019 1:59 pm I found LT1 seals are the same dimensions

On LT1's and L31's etc from that era....these engines have a different intake and exhaust valve stem seal. The aftermarket tends to just sell 16 of the same intake seal. I like to use the GM seals in applications where the guide diameter allows. GM part# 10212810 for the intake(black in color), GM part#12564852 for the exhaust(orange in color)...lighter tension spring on it.

They are sold individually and the price kind of adds up. I've used that orange lower tension exhaust seal quite a few times...on intake and exhaust.

I've also pulled the springs off the exhaust seals as well, like previously mentioned. ..but that was mostly on the Teflon pc seals.

Yes the Teflon is was what I was thinking, I got some orange ex seals on my last go round, I just don't remember where I got them.

turbo camino wrote: ↑Mon Nov 11, 2019 5:04 pm I think I'll try it with no seals on exhaust. If it doesn't work it won't break anything, I can add seals later if it's a problem.

It will most likely blow a puff of smoke at start up like you have a bad valve seal...

If it smokes too much from too much oil that's easily fixed, too little oil and a stuck stem with the head broken off and stuck through the piston top and the cylinder wall blown out is a bit of a bigger job. I don't think the umbrellas on there now are doing much of anything anyhow.

I have been putting the positive viton seals on both intake and exhaust for years now. Have not had a problem. Thats how the cast iron Vortec heads are. I have been using that type on 502 marine engines too with no problems. Virtually all modern engines have the positive seals on both intake and exhaust.

Howard’s Viton. Summit. No issues.