Hey,

I'm doing the valve seals at the moment on my A12 and just realized that there is nothing to stop them staying on the head?!

I was under the impression that they stayed on the head and the valve slid through the seal but now they kind of look like they stay on the valve stem and kinda of reciprocate with it and act like a shorud to stop oil getting down the valve stem?

FYI my new valve stem seals look just like my old ones which are a domed black piece of rubber with a hole through it.

Am I missing something or is that how they are meant to run (fixed to the stem)?!

The valve stems seals tend to be more useful on the intake valves, the minute vacuum produced (remember these are the intake valves so there is suction/vacuum on intake) keeps them down the bottom where they are most effective, keeping a decent seal. What little fumes escape through or past the exhaust valve stems/guides are expelled through the outlet at the top of the rocker cover, along with all the other fumes.

What you have is the umbrella sort which is basically a shroud. The better ones have a little spring collar that grips the valve guides, these are most effective when there is a groove cut into the valve guides to allow a decent connection. I will try and get some photo's if that'll be any help explaining things?

I know what you mean because when we rebuilt a mates L28 he had the spring clip retained seals - where as I have a shroud type one.

Having said this, when idling you can see orange flashes through my glass spark plug I use to tune the idle circuit. The proper color should be an oxy torch blue and orange flashes indicate oil burning. At idle it creates a high manifold vacuum so what I thought is that my valve stem seals are worn...but if in fact my A12 uses shroud type seals (that cannot wear out) maybe my valve guides are worn?

How else can oil get into the cylinder under high vacuum? How much wobble should the valve have when the spring is off and I can wiggle it by hand?

Having said this - can I install the "proper" (positive seal type) valve seals on a head that originally ran shroud type seals?

You can install positive lock type stem seals without machining a groove in the guide but they can pop off.
I just had my head reco'd and got them to machine the groove in and fit the positive seals, worth the effort I reckon.

Ah wicked - dont suppose you know what engine the seals came off that you used? Just any L series?

Also, I plan on running the positive seal type on the inlet and umbrella on the exhaust. Umbrella on the exhaust will lubricate better and thus transmit heat out of the ex. valve better.

Now if the engine burns oil on idle, is that common of umbrella seals OR does that mean my valve guides are worn out?

Those positive seal kind (stays on the valve guide) don't work too well when the guide gets a little worn.

And the O-ring type seals are only partially effective.

I recommend Ford-type "umbrella" seals on both intake and exhaust valves. These stay on the valve stem and go up/down with the valve.

That's what I have now but on high vacuum situations my engine burns oil so I guess my valve guides are worn?

Were is the burnt oil coming from? If the engine is 'burning' oil, it's coming out the exhaust, which means you would most likely have an issue with your piston rings. A compression test is a good indication of how well things are sealed.

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Most likely, although there is a small possibility the rings are bad. Do a wet & dry test to tell for sure.

If it is the usual valve guide wear, then umbrella valve seals will clear up 80% of the problem, and do not require you to remove the head.

I have umbrella seals now and it burns oil at idle (while driving its fine - no smoke, plugs are nice and clean).

Thats why I wanted to put positive seals on the intake valve stem just for now so I can tune my carbs a little better then when I rebuild the engine I'll get the valve guides done.

Does any one know of a positive valve seal that will fit A series heads? (a drop in replacement that requires no machining to the guide)