Originally Posted by Nuck Chorris
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.
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.