Maybe this question sounds a bit stupid...

I will start to replace the old valve stem seals with new ones:

FELPRO SS 72527 for the intake valves
FELPRO SS 72877 for the exhaust valves

In the seal sets I've found the seals and a set of the O-rings.

Now my question is:
Do I only have to replace the valve stem seals or the valve stem seals AND the O-rings too???

Where do I have to install the O-rings?

 

By searching Google I found the following:

"The o-ring valve stem seal goes on the SECOND grooved notch of the stem"

I think this answers my question.

 

I used the Positive type 72527 for both intake and exhaust. The 72877's are umbrella type and not Positive type. And yes you change both the o-ring and the valve seal.

 

There were some posts in my search results that say that using the intake seals for the exhaust may have pose a shorter life because of the heat. Were they the rubber kind?

 

i use both, doubt it help but i'm sure it doesn't hurt either

 

Positive type 72527 are made of Viton. Should hold up fine on exhaust.

 

I know this is an old thread, but I am doing the same job on a 1990 350 TBI. I have SS72527 and SS72877. The SS72527 is the intake positive seal, which came with BIG rubber o rings; SS72877 is the exhaust umbrella seal which came with small square o rings.

The problem is the big o rings that came in SS72527 with the positive seals are loose in the second groove of the stem and they're way to big to install with the spring cap/retainer on and compressed... I don't get it, the exhaust was straight forward. I put on the umbrella, then the spring and retainer, compressed them, installed the little square o ring in the second groove, then the keepers, relaxed the compressor - done. But, the intake side is not working out like that... The o ring is enormous. What the hell? Did they give me the wrong o rings? lol

 

Forget the o-ring on the intake side. Not needed. Today's positive seals are viton which is miles ahead of the old rubber seals used by the factory back in the 80s. FYI- you can also use them on the exhaust side by themselves if you want (no o-ring), but getting the intake side sealed up tight is 10X more important than the exhaust side. Some engines (endurance/road race applications) I don't even put a seal on the exhaust. I figure the exhaust valve is getting the snot beat out of it for hours on end it can use as much lubrication as it can get to keep the guides alive.

 

I omitted the o ring on the intakes like you said. I did put the proper-looking squared o rings on the exhaust since they came with the exhaust umbrellas anyway. Honestly, I am not sure I got them all in correctly in the groove, but I am not too worried about it. It turns out it didn't have any seal besides old rotten o rings on the exhaust, so it should be much better off with the umbrellas on there at least.

I used compressed air to hold the valves shut. I heard air escaping and the compressor would keep turning on for all the cylinders. Then I got to the last cylinder and it was so bad it wouldn't even hold the valves up. All the air was escaping out the intake port. My heart sank. I thought I had a bad valve. But, it ran so well... I put a piece of wood atop the valve and hit it with a hammer several times. Then it sealed, much better anyway. I don't know if it was carbon or gasket pieces holding it open or what...