Guys
Advice and opinions please. When the brave day comes that I rebuild my engine, all parts having been gradually accumulated beforehand, I want to be as clued-up as possible.
I have been finding out about valve stem oil seals, and there are a variety of materials used, apparently:

1. OEM nitrile seals - these fail after a bit apparently.
2. Viton seals - this is a more durable material, FelPro make them, but I do not know if they make a size suitable for the 5.3 V12. Neither do I now if a Viton seal is thought to be good material to use in the V12, if they can be found.
3. Teflon valve seals as recommended by the Great Palm. Apparently part number DT1610 fits.
4. Lastly, although no seals are fitted to the exhaust valve OEM, Viton and Teflon seals are alleged to stand up to the heat, so is fitting a seal to the exhaust valve stem recommended?

So to summarise: Which material to use? Exhaust valve stem or not?
Cheers
Greg

 

Hello Greg. I will jump in on only the final question . . . efficacy of fitting stem seals to exhaust valves . . .

Back in the day, and I admit this is at least 20 out to 35 years ago, despite universal use of inlet seals, it was considered of no use whatsoever to fit such seals to the exhaust valves, whether for road or track or in our case, on "Jagged" our unlimited twin turbo'd V12 Jag hydroplane. Reasons were backed by plenty of experience . . . seals are all about inhibiting cylinder negative pressure from drawing excess oil into the combustion via inlet valves.

So,even in "blown" engines, provided exhaust valves were well lapped to their seats, by the time they were opening, even with competition camshaft overlaps, the cylinders had positive pressure so oil was never going to be drawn into cylinders . . . making any exhaust seals totally redundant.

Sorry I can't provide any reliable knowledge of relative merits of materials for inlet seals.

Cheers,

Ken

 

If the teflon seals are similar in price I would go with them, I'm using Viton for mine as this is what Norm gave me. They will probably last longer than me with the occasional use my car gets now.

 

Warren
Do you have a part number or a maker ? I am a bit more inclined towards Viton as thye are meant to be a bit more forgiving and easier to fit than Teflon ones.
Greg

 

That is most interesting Ken, thanks for the post.
Greg

 

Agreeing with Ken, or rocks will land on my roof from afar.

I used OE and did the Inlet only.

I always liked a little "lube" down the exhaust valve stem, they do get a tad HOT.

No seals on the Inlets will suck the sump dry eventually, and make a hell of a mess.

Then,

My totally Non-Scientific reasoning behind what I did.

1) Jag only supplied 12.
2) "Oils Aint Oils", and the current spec oils are kinder to all sorts of non-metallic components, stem seals included.
3) I have the cooling system well sorted, so the engine, and its oil, do NOT get out of temp range, ever.
4) The V12 cam shaft area is significantly "drier" than the older XK 6 cylinder engine, which basically bathed the cams and buckets in oil.

 

So basically, Grant, you think the OEM ones are quite durable enough? I will forget about the exhaust seals.


Greg

 

Hi Grant...quick question having not rebuilt a 12 yetttt. Can the Valve stem seals be done with the heads on???

 

i have had Teflon seal all lube from the Exhaust and wear guide and stem quickly, like 5000 miles! HE exhaust run very high temps ,relative to Pre-HE.

i had a Rotary Mazda turbo, made 430hp FAST! pic in profile.

 

Nice mine is a gen one car 900kg 450rwhp not the car to take on a wet road, you'll know what I mean.....

 

Greg,

Yep, they have survived 30 years and NO issues, so in the next 30 years, YOU and ME will be looking down from the Jag place in the clouds and laughing our aarses of.

PLUS

The egg timers up there move at half pace, so we will be too busy.

 

Nope.

That $600 chain tensioner will need "fiddling" with to get the cams off, not for the feint hearted.

Then the risk of dropping a valve into a cylinder is right up there with BUGGA.

Stem seals on a V12 are not a known issue. Most all oil smoke is from driving too sedately, drive it like ya stole it, perfect the V12 grin, and move on.

 

Makes me feel a whole lot better about the inevitable!
Greg

 

Holding the valve up doesn't worry me the chain tensioner does...... A freinds car has out of the blue started to oil up a plug 1A to miss fire point within 15 minutes of running. My immediate thought was a valve stem seal....30 years old.

 

Doubtful.

More likely oil coming up past carbon jammed rings.

If it were 5 or 6 then maybe stem seals, as that is the hottest part of the engine.

Our HE engines are the Hi Comp units at 12.5:1 ratio. Lack of use at some stage of its life could also be at play here.

My PreHE's do oil up #3 on each side, but a decent redline blast for a few hundred kms takes care of that for a year or 2. Our stupid 50KPH speed limits are very V12 unfriendly.

The HE's never did, and I did find the Red Devil had seriously stuck rings when I pulled it down for oil leaks, oops, and that really surprised me due to it not burning any oil, just leaking it. The original owner used it in and around Adelaide only, never drove it as designed, so not surprised at all by what I found. The stem seals were still very pliable, and the stem to guide clearance quite good, but it got new valves anyway.

Maybe a good hard run will help it sort itself.

 

How are you going to remove the spring with nothing under the valve head. I think valve seals are a head off job. I would also check valve springs.

I'm rebuilding an ex USA V12 ATM and from what I've seen every valve stem was elliptical and every spring not straight.

 

.

warrjon , there is a way to use compressed air to pressureize the cylinder with piston at top of stroke, done that CAREFULLY a number of times !!

there is also a kit available , Summit racing or some such,

i used a fiddled together air hose and adjustable valves ,with gages to measure pressures! screwed into the sparkplug holes!

ron

 

Correct or rope.........I have placed rope into the bore through the spark plug hole and gently wind the piston up until it's pushing the rope into the valve head....works a treat.

 

Agreed, and I have used the Comp air at BDC a few times, still scary as hell though.

The rope is OK on all but the V12, as winding that engine backwards to get the rope out MAY/WILL break that $600 Plastic boomerang, so back to square 1.

 

Assuming rings are in god condition and leakdown is very slow. Took me ages to get the keepers back on with cam carrier bolted on with head on the bench, being lazy as I had already glued it on and didn't want to pull it off and clean the Loctite off, anyway I ended up pulling the cam carrier.