SBC head casting 3917291, guide boss is about .580, 11/32" valve stem. It had umbrella type seals that were hard, cracked, broken and were hung up in the double valve springs.
So I don't need to use the positive type seal or umbrella seal ? Just the o-rings on the valve stem ?
I have used umbrella type seals from a older Cadillac V8 (not sure of the size) in a small block Chevy that were recommended by a machinist friend years ago, seemed to work fine without any modification. I am sure there are better more expensive new seals that work better now, all seals get hard and fail after many years of heat cycles and use. There are better materials now but some of the "off shore" seals are made of materials that fail in short order. A friend ordered a very inexpensive gasket set from Amazon for his small block Ford and it came with umbrella valve seals in the set. Two years later the oil pump seized and twisted off the drive shaft, we found pieces of the valve seals in the pump and that's when we realized the seals were coming apart. In all fairness, this friend has been known to run some pretty weird additives in his oil. Just sayin....
as long as it has the metal cup over the spring, the O ring should be sufficient. But some guys add a positive seal over the guide, just because. A quick look shows that the normal "universal" sizes won't fit unless you machine the guide some more....
I have heads re-done in the past that use the stock O rings and heads that had the umbrella seals installed. I have not noticed a difference in performance either way.
Those heads came from the factory with only the o-ring and that’s all GM thought was necessary. If you have guid and stem wear an umbrella style seal wouldn’t hurt. When working in the rebuilding business we always installed umbrella seals and the o-ring it was pretty much the standard in the industry at the time. Mostly for insurance and a selling point. .520 is the most common guide OD to use with an 11/32 valve stem. I think a .580 is available but may not clear the damper spring. I haven’t done this work in a long time and unfortunately don’t have a good brand to recommend. Seems everything has gone down hill. I will say I was never a fan of the felpro umbrella seals.
Whatever seals you use, if you're replacing them without removing the heads then get this spring compressor. https://www.summitracing.com/parts/sum-906784 I'd seen a video on YouTube where a guy was using it so I bought one when I needed to replace the seals on the 4.3 V6 in my DD pickup. It works really good in general, but it really shines when you start to install the locks back onto the valve stems since the design gives clear access to the stem . The old star wheel type compressors make it difficult to know for sure that the locks are engaged in the grooves and every time I ever used one I figured it was just a matter of time until I ended up eating a spring when the locks decided they weren't in just the right place.
There were no O-rings on the valve stems, but I am in the process of removing the old umbrella seals and installing the o-rings. Only 12 more to go.
Umbrellas are hard to beat on a stock type SBC head,,,,,I never liked the o rings,,,,,unless the guides are new and tight . Umbrellas work good on stock type Mopars as well . Full umbrella on the intake,,,,,half umbrella on the exhaust . Tommy
When I was doing valve jobs for a living, I would see lots of Chevy heads come in for oil consumption with improperly installed o-ring seals. When they are installed correctly along with the metal cup shield on the spring, they work fine. Don't just push them on the valve stem then install the spring. They need to be in the groove in the stem and inside the retainer to do their job. They will not work themselves into the groove from under the retainer. Compress the spring first, install the o-ring in the groove, then install the keepers and release the spring
I bought a car that the PO had “just put new o-rings on” yet still smoked in start up and decell. So I popped the the VCs and was about to pull the heads and my dad said to pull a spring first, that’s when I noticed an o-ring on the valve stem. So a few hours later pulling all the doings and putting the o-rings in the right spot helped a lot, guides were still shot but at least it was a lot better. But GM went to the seal around the guide in the mid 80’s? I think, it is a much better set up.
Chevy started using positive seals on the intake and umbrellas on the exhaust when they found that oil past the guides was fouling catalytic converters and causing emissions failure. If I knurled guides on a SBC, I always used umbrellas on intake and exhaust in older heads that weren't machined for positive intake seals. But I also installed the o-ring like the factory did.
If you install non- umbrella type seals similar to the ones in the picture, be sure you do a valve movement check to insure that the spring retainer does not contact the seal and that the valve springs clear the seal. Don't want any contact with the retainer, and not all non-umbrella seals are the same. Note: I edited this post as I had previously said "umbrella" type instead of the cprrect term "non-umbrella" type. Thanks to Desoto291Hemi for catching that mis-statement.
Those are not umbrellas,,,,, Those are a type of Viton seal,,,,,and the guide o.d. Has to be cut to the correct size for fitment. And it is usually a good idea to go ahead and cut the guide height down a little while you are there for good measure . Tommy
I want to thank everyone for the replies. That's the exact spring compressor that I have, when it is adjusted correctly it will fully compress the spring and lock in that position so you have both hands free. Hopefully I'll get this engine installed in the next few days and see if it smokes any.
early 472 Caddy umbrella valve seals fit with no modifications. We would run them on our junk yard enduro round track race cars and our $ 300 claimer motors.
I would stick another set of umbrella seals in them, there is more than likely a little too much clearance in the guides and was the reason they were installed. We used 2 sets of Vega valve seals, they were cheap and when you couldn't afford machine shop services, it would really slow down the oil consumption. Good luck
Many big chunks did not make it past the screen but lots of tiny ones did. Screen was not damaged that we could see but pump would not turn so we pulled the pump apart to see why. Big chunks were easy to identify, we assumed the small chunks were more of the same. Engine had 11K miles on it and otherwise was very clean inside.
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