Valve guide seal exhaust valve?

Hi!

in the exploded view of the cylinder head parts [1972, sheet g2] there is no seal for the exhaust valve. and I never had no seal on the exhaust valve guide......just a thought:


Do you think there should be one or leave it as it is? Why no seal? got some experience?

I can`t get it why they left the seal on the exhaust valve guide.....


chris

Typically a seal is not fitted to the exhaust side as it doesn't suck oil into the cylinder when it leaks as the intake side does. I suspect the root of that is due to higher temps that would shorten the life of the seal but I don't know that from first hand experience.

Russ

True...

but exhaust seals are regularly fitted on "modern" engines and retrofitted on older engines. Although exh valves/guides cannot pass as much oil as intakes can, it was found that the venturi effect of the the exhaust gasses rushing out of the Cyl head can pull oil past the exh guides. So now it's considered correct to fit exh seals to engines that originally did not have them.

As an example, my '91 Ducati 900SS did not come with exh seals but I received a factory notice maybe a year later that stated Ducati dealers would install exh seals on the bike for some minimal flat fee. Any good engine builder - at least performance oriented building - would install exh valve seals on an old conventional US V8 even though they may not have had them originally.

On the Ducati, the seals were different color so I assume the material on the int/exh was different. On seals for US V8s that I have worked on, they were the same - Teflon, if I remember right. (We know how well the "memory thing" works... or doesn't! )

Fullauto Technologies heads are fitted with the same guides on inlet and exhaust and therefore have a groove to retain seals. Otherwise a normal automotive seal of the right size which uses a spring to hold the seal on can be used. In Australia, these are available for the Holden V8 engine.

My '99 Buell X1 has exhaust and inlet valve stem seals. Both are the same part number.

when I rebuilt the heads on my 750 and 850, I didn't bother about valve seals. the bikes don't smoke.

kerinorton said:

when I rebuilt the heads on my 750 and 850, I didn't bother about valve seals. the bikes don't smoke.

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+1. In addition I left out the valve guides, piston rings, engine, gearbox, primary drive oil seals and any thing else designed to reduce oil consumption. No leaks and the bike uses no oil - works for me!

when I rebuilt the heads on my 750 and 850, I didn't bother about valve seals. the bikes don't smoke.

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I'm not going to make a sarky comment but when my inlet seals have failed the bike has smoked lots at startup and had oily chambers. It was either due to me fecking the installation by overcompressing the spring or by a supplier as recently supplying two different seals! Both very similar but one quite a loose fit on the valve. I'm assuming Norton added the seals because of excessive oil consumption.........after all they were unlikely to spend on something that was unnecessary. The early bikes were seal less, does anyone know when they changed?

Keith1069 said:

The early bikes were seal less, does anyone know when they changed?

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From 149670 (mid-late '71).

These inlet seals do just whats expected ,they keep 90 % of the oil from getting sucked into the engine, early dommies had return line feed, well more of a dribble. when positive feed was introduced this forced oil into the head . I built a commando engine ,and one inlet seal "popped off" it smoked bad on that side.
Its a catch 22 , seals do just that..they seal the valve from oil...how good are they at starving the stem and guide from vital lube, well that's another question? Cast iron guides are self lubing ,and tolerate no oil better than bronze. Mayby a small hole in the seal would allow just enough oil, whats better, a tiny haze in the zorst,knowing the valve is getting some lube ,or no smoke and dry guides? I guess most owners are hung up on any smoke?
And before "we" start quoting Modern machines, Remember not many have the Norton two valve "high thrust" rocker arms..OHC is much kinder.

:?: Unlike a NHT in a featherbed...commando intake valve stem is almost vertical. When oil gets on it, it continues to ride up and down, and more inclined to get sucked down the guide and not get scraped off and shed sideways. The exhaust which is at a large angle from verticle might slide off the top of the guide toward the front of the engine then drain down the push rod tunnel. :idea:

This seems like a good place to point out that smoking due to sucking oil through the valve guides depends a lot on the stem-guide clearance. I've never run seals on my race bikes, but the all had bronze guides and tight fits to the stems. They don't smoke except when cold, and I don't see a lot of carbon buildup on the back of the valve head. The stock iron guides require a larger clearance, and will smoke if the seals are left off, particularly if the engine has some miles on it. I always use the seals on stock heads with iron guides.

Ken

lcrken said:

This seems like a good place to point out that smoking due to sucking oil through the valve guides depends a lot on the stem-guide clearance. I've never run seals on my race bikes, but the all had bronze guides and tight fits to the stems. They don't smoke except when cold, and I don't see a lot of carbon buildup on the back of the valve head. The stock iron guides require a larger clearance, and will smoke if the seals are left off, particularly if the engine has some miles on it. I always use the seals on stock heads with iron guides.

Ken

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Ken,

When I suggested leaving the seals off on my Fullauto head...a couple of weeks back...everyone....I mean everyone including those who supply the head/seals...said....'don't do that'...

I should have a box of assorted seals to play with at home now, so I can select what I am happiest with....but I still wonder....race motor in vertical rigid mount frame.....new Fullauto so new bronze guides, and Black Diamond valves....nice tight fit....new motor likely to be stripped again over winter after very little running.....just to see how its bedding in...

At least your comment makes me feel that no seal at all is another valid choice in my particular set up.

Still, plenty of time to juggle all the opinions and options again. I don't get to the workshop again until the 9th!

Thanks

You can get away with oil contamination in the combustion chamber of an engine stripped down every few hundred miles, but on a high miler hard carbon particles will deposit on the ex. valve seat and valve causing pitting and leading to poor sealing. Cutting the seat and new valve is the only solution but this accelerates the wear rate and means components require changing more often. Road or race it makes no sense leaving out the seals.

Al-otment said:

You can get away with oil contamination in the combustion chamber of an engine stripped down every few hundred miles, but on a high miler hard carbon particles will deposit on the ex. valve seat and valve causing pitting and leading to poor sealing. Cutting the seat and new valve is the only solution but this accelerates the wear rate and means components require changing more often. Road or race it makes no sense leaving out the seals.

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Reality is that I am most likely going to fit seals....particularly after the effort of me and others to get them....all I am really saying is that there is at least one advocate of the alternative not too...and someone with far more exerience of race motor builds than either of us.....on the other hand....there are those with plenty of race motor experience who use seals....

I can completely agree that if you are doing a lot of road miles you don't want to be stripping and reworking and replacing parts every year, or plugs every few thousand miles, let alone carrying a lot of top up oil.....of course you would fit seals.....but this simply does not apply to a race motor, for one reason or another you are going to rework/replace those parts anyway, and most would change oil for each meeting anyway....whichever oil they choose and whatever they pay for it.....and plugs have a fairly short life being changed even if not needed...

As for valve seats, for a race motor you run them with a very narrow contact area and they won't last that long anyway.....

Racers are not totally rational.....some things you spend more on give you reliability, but in the search for performance most things you spend money and time on will cost you even more in the end due to part lifing etc. :roll:

'As for valve seats, for a race motor you run them with a very narrow contact area and they won't last that long anyway.....'

If you raced every month on a 3Km circuit having at each meeting five 5 lap races and four 5 lap practices at each meeting, it would be like riding your street commando to the local supermarket and back. The shape of the valve seats is important and if a small piece of a cast iron valve guide breaks and dents the seat and valve, that has more effect than wearing out. I knew the edge had gone off the motor but I didn't find it for about four race meetings

I guess I should be clear that I wasn't recommending leaving the intake valve seals off, just pointing out that race bikes run fine without them, and discussing why. Axtell and Ron Wood didn't use seals on their guides, and that's where I picked up the habit. Like Al-o pointed out, race bikes generally get regular maintenance, and don't do high mileage, compared to street bikes that are regularly ridden. When I was racing regularly, the engines got torn down and inspected at least once a season, and always got a valve and seat cleanup. The current technique for modern high performance engines seems to be using seals on both intake and exhaust guides, and the competition guys seem to prefer the spring-loaded Teflon style. That's probably what I'll use, at least on the intakes, along with bronze guides, on the two street Nortons I'm rebuilding this year. I worry just a little about having enough lubrication on the exhaust side, so might leave seals off them. I'll still leave the race engines without seals, unless I come up with some compelling reason to use them. The only use the race engines get now is for landspeed racing, and that's very low mileage.

Ken

lcrken said:

I guess I should be clear that I wasn't recommending leaving the intake valve seals off, just pointing out that race bikes run fine without them, and discussing why. Axtell and Ron Wood didn't use seals on their guides, and that's where I picked up the habit. Like Al-o pointed out, race bikes generally get regular maintenance, and don't do high mileage, compared to street bikes that are regularly ridden. When I was racing regularly, the engines got torn down and inspected at least once a season, and always got a valve and seat cleanup. The current technique for modern high performance engines seems to be using seals on both intake and exhaust guides, and the competition guys seem to prefer the spring-loaded Teflon style. That's probably what I'll use, at least on the intakes, along with bronze guides, on the two street Nortons I'm rebuilding this year. I worry just a little about having enough lubrication on the exhaust side, so might leave seals off them. I'll still leave the race engines without seals, unless I come up with some compelling reason to use them. The only use the race engines get now is for landspeed racing, and that's very low mileage.

Ken

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To support your comment that race bikes work without inlet seals.....I have just gotten home from Cadwell Park...amongst the people I spoke to was Dave Watson, owner of the 1007 Seeley Commando that Gary Thwaites used to ride up to last year....(he still has that bike if anyone wants a proven winner)....

Valve seals....haven't used them in 40 years says Dave....

Just another racers opinion....