Umbrella or positive valve seals?

[airman]

I have a 351W built 25 years ago by PO and using oil. My valve seals are hard as a rock and cracked. What is coming off looks like an umbrella but was tight fit on the guide and worn as if it were stationary like a positive seal. I'm interested in opinions on making this choice. I'm having trouble finding many pros and cons out there.

 

[73azbronco]

Usually when you get to your point you also do a valve job, as the guides or stems are worn as well. By the time you pull the springs off each valve, might be easier to pull the head and freshen up the heads.

 

[airman]

Usually when you get to your point you also do a valve job, as the guides or stems are worn as well. By the time you pull the springs off each valve, might be easier to pull the head and freshen up the heads.

If I take a step down this path and knowing myself, it would turn into a complete new drivetrain. Its a deep rabbit hole I don't feel like going into.

I'm just looking for opinions on seals.

 

[Apogee]

The umbrellas have worked fine for years and years, so if you want to just freshen up the heads at minimal cost, then I'd just stick with them. Now it is 2021, so if you want to machine the heads for positive seals, then just pay the money and get the more modern solution and all of the pros that go with them: higher quality material (viton), better oil control, longer life, better valve spring clearance, less likely to cut/tear/end up in the bottom end, etc. There's a reason they're the new standard.

 

[airman]

The umbrellas have worked fine for years and years, so if you want to just freshen up the heads at minimal cost, then I'd just stick with them. Now it is 2021, so if you want to machine the heads for positive seals, then just pay the money and get the more modern solution and all of the pros that go with them: higher quality material (viton), better oil control, longer life, better valve spring clearance, less likely to cut/tear/end up in the bottom end, etc. There's a reason they're the new standard.

Thanks, They have been machined to .500 already.

 

[bmc69]

I'd definitely stay with the positive seals. I do the machining to use those on every set of older heads that I build.

 

[Rightpace]

I would go with the updated positive valve stem seals, the umbrellas are outdated.

 

[73azbronco]

If I take a step down this path and knowing myself, it would turn into a complete new drivetrain. Its a deep rabbit hole I don't feel like going into.

I'm just looking for opinions on seals.

I had leaky valve cover gaskets that turned into 12 year resto.

 

[airman]

I had leaky valve cover gaskets that turned into 12 year resto.

I had an overheating issue (eventually found gummed up mechanical advance staying thrown out) that turned into new cooling system, serpentine pulleys, Vintage Air, EFI, all new fuel lines and pump and all new under hood wiring. down for 18 months. I know a little of your pain

edit, forgot: motor mounts, new pan, new body mounts, door hinges

 

[BrownDog]

My 74 was driven 500+/- miles for the last 5 years. When my uncle finally passed it on to me it smoked like crazy. All the umbrella seals were dried and cracked. I replaced with positive stop seals. Not a bad job at all