Beater79TA

A few weeks ago we noticed our recently acquired 90 IROC vert was blowing a small amount of smoke at startup if it had been sitting for a day or so. Knowing that the primary cause of this is the valve stem seals, we acquired a set to do the repair. When we opened up the valve cover and got the springs off, we noticed none of the exhaust valves had the caps on them, just the o-rings? Is this normal on the 305 TPI's used in the 90 IROC verts or did someone do an incomplete repair at some point?

Gramps

iTrader: (1)

they used either the orings or the umbrellas, i am about to do this myself and am going to be using both orings and the umbrellas.

l_dis_travlr

I'm not sure when, but for some time GM has only been putting the umbrella
seals on the intake valves. Look at the retainers -- the exhaust valves have
a shroud element included, which in conjunction with the o-ring is deemed
sufficient. I've seen some older literature that confirms this configuration,
but nothing that explains it. Speculation: oil leaking down the intake will
adversely effect combustion (VE ratio, plug fowling, ???), whereas leaking
down the exhaust just get gets blown out the tailpipe. Probably also a
cost control thing. I've got a major rebuild in progress, and head service
will include umbrellas on BOTH valves --or convince me why it's not a
better way.

good luck,
kk

five7kid

iTrader: (14)

Intake valve has vacuum on it that tends to pull oil past the valve stem & guide and into the cylinder.

Exhaust valve has pressure on it that tends to push oil away from the valve stem guide back into the valve cover/rocker area.

When the engine isn't running, oil on the exhaust stem can run down the guide and into the cylinder if the valve is open. Or burn in the exhaust stream after the engine is started until it's gone. Producing blue smoke out the exhaust upon startup.

Beater79TA

Ok. So this is normal then. It did surprise my mechanic though when he saw it. We're installing the umbrellas on the exhaust while replacing the ones on the intakes though. The car doesn't get driven that much so there is plenty of time for oil to leak down through the exhaust valve stems.

Now for the follow on question? Is there any reason to not put the umbrella seals on the exhaust valves?

Apeiron

The only reason to not use umbrella seals on the exhaust would be if you're going to use a positive seal instead, like the intake valves have.