Ford racing Z304DA valve stem seals: umbrella vs positive

[tortuga]

So in poking around trying to get to the bottom of my 427/535 sbf, I've surmised that the valves have "umbrella" type valve seals as opposed to positive type seals which attach to the valve stem bosses vs riding on the valve stems.

Is this a fairly straight forward swap or do the heads need some machine work to fit the positive type seals? I am also thinking about doing this over the fender using compressed air to hold the valves while the springs are off?

Thanks
Steve H
SPF 1764

[spdbrake]

Yes those are Umbrella seal on those heads.

The air fitting will work. Putting the cyl your working on at TDC will save your Compressor as you look for whatever tool you just set down somewhere...

You may or may not have to machine the valve guides OD to fit the Positive Seals. Depends on the measurements. You will have to pull the heads and remove the valves to use the guide cutter.

While I'm really not against Positive Seals, since they lube the valve stem and guide from the top gap the seal top gap is critical. Too small you burn up the guides and valve stems, too large and you have a smoker.

Working on KISS principle going back with Umbrella seals (possibly a better material than you currently have) is not a bad way to go. https://www.enginebuildermag.com/199...s-and-designs/

[tortuga]

LOL yep, got it...just seems like the umbrella seal are sort of a silly idea...with some research (including a call to the FRPP tech line) think I can hopefully track down the exact right bits and what needs to be done.

Maybe best to just pull the heads and take them to a machine shop, but then I'm at the mercy of the whims of an overbooked business...but hopefully it's all done right.

Steve H
SPF 1764

[Gaz64]

Heads off, stripped, light valve spring fitup on two valves, check for retainer to guide clearance at max valve lift to suit current camshaft, machine top of valve guides for positive viton seals that still allow adequate retainer clearance, machine valve guides for bronze guide liners, recut valve seats concentric to new guides, inspect valves for continued service, clean or replace as necessary, resurface heads, clean, reassemble heads.

I like to seal the valve locks in the retainers after assembly, prevents oil running down the stem, they only need the odd splash, if running a bronze guide liner.
Cast iron guides do not survive with reduced lubrication.

Gary

[tortuga]

So I think I've finally figured out my oil consumption, I DO have a couple of leaky seals: drove it yesterday and tried my damnedest to do a lot of engine braking (trying to draw as much vacuum as possible) checked the plugs and viola #'s 2 and 7 had light oil and we're obviously a little wet:
SOOO,
The umbrella seals work in 6 of 8, two are sketchy...so I think I need to fix those two with what works in the other 6. I'm betting two bad seals.
Weird thing is that the bad two are in the same cylinder if the identical heads are laid next to each other?

Steve H
1764