Valve seals

[390owner]

What is the best valve seals for my 390?

[GerryP]

Viton.

[Tunnelwedge]

The stock 390 used a rubber umbrella seal. Works good stock.
There are some positive lock seals to fit a stock guide, Mahle I think.
What heads do you have and what do the guides look like?

[390owner]

It has stock heads. I had it rebuilt by a machine shop I use about 20000 miles ago. It is smoking while holding back my camper going down hills in 3rd gear. I called the machine shop and he said sounded like it needed new valve seals.

[Tunnelwedge]

Probably good to follow his advice.
Stock umbrella will be the ones.
They go hard and brittle after a while. 20,000 miles is a while.

[Diogenes]

I had a smoking problem back when I purchased my car. I used Comp Cams p/n 514-16 on my stock heads, and they have worked well.

[pbf777]

      I'm not going to pretend like I could tell you the solution to the oil control problem your vehicle seems to be suffering from standing here; yes, seals could be a participant, but his actually often is only in conjunction with excessive valve guide clearance too.  But so could the piston rings be a cause, as remember rings utilize cylinder pressure to aid in their seating and on a long downhill run with the throttle closed your not making a lot of pressure to aid the rings in seating or participating in oil displacement through "blow-down" either.   

      Also, the fact that umbrella seals may become "hard" doesn't really change their effectiveness, they're actually not well defined as a seal at all, rather they would be better described as an umbrella "shield" or "oil-deflector";  that is until they crumble and fall off!   

      B.T.W. the Comp-Cams #514-16 will not properly fit "stock" heads, as they are intended to press over a .500" guide boss O.D. (these are not an "umbrella" seal) and this the "stock" heads do not present, unless they have been machined at a later date for such.   

      Scott.

[My427stang]

There are positively located seals that fit an FE guide, but they are pretty big and depend on valve spring choice and retainer to guide clearance.  US Seal sells by dimension, but here is an example from another source. 

https://alexsparts.com/3-8-x-625-660-viton-valve-seals-flex-body-type-fe-ford-universal-vss-407-set-of-sixteen/

I agree though, good guides first, then if doing a valve job anyway, put real guides in (consider a 11/32 valve), cut the locator pad off and run a real locator and a nice Viton .531 seal.

If the heads are nice, you could just pull them down and cut the existing guide, but sometimes you will have retainer to seal clearance

As far as which brand of seal, I really like Manley Viton, Brent turned me on to them many years ago.  They push on easier, hold tight and last well.  It's all I really use now

[390owner]

He built the entire engine including the heads. This is the second 390 he built me. I bet the guides are fine and within tolerance   If it is the valve steam seals why does it not smoke when I first state it

[GerryP]

You started this thread on the topic of stem seals and said your mechanic felt it was stem seals.  It might be seals, but that's not where the smart money is.  A great stem seal will fail quickly with bad guides.  A really good guide can pretty much function without a seal.  Particularly on the exhaust.  As to what it can be under heavy vacuum if not a valve guide issue?  It could be bad intake gaskets.  It could be a flooded or stuck open PCV.  It could be pulling oil past the rings.

[Tunnelwedge]

A few things are happing with the seals.
The stock umbrella seal when new hugs the valve stem and rides down and up
with the action of the valve. The oil that cascades down from the rocker is defected by the
umbrella. When the seal gets old and hard it does not ride the stem anymore and sits on
top of the guide and this allows the oil to seep past into the chamber.
When you are going down hill and using the engine brake that allows the oil to accumulate
on top of the head. This is also when you have high vacuum in the intake runners.
You could be sucking oil in from a intake gasket also.
When doing a cold start all the oil has drained away and you are doing a dry start.

[1964Fastback]

Re. PCV, if you have the usual setup with it in a valve cover (mine is the old style at the back of the intake), an easy test would be when you come to a hill like this, stop and pull the valve out of the cover but keep it plugged into the hose, just hanging free.  Then go down the hills and see if it is smoking less.  Could be oil mist sucked in through the valve because of a missing or bad baffle in the valve cover or excessive oil mist.

Sure, it might be guides, seals, intake or a combination.  But I like free and easy tests.   

Pat