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MG MGB Technical - valve stem oil seals

has anyone any information on fitting umbrella type valve seals to an 18GG engine good idear or not also part number of these seals thanks
andy tilney

A good engine shouldn't need them or they would have them anyway. If the valves/guide are worn it might reduce consumption a bit. On non-worn parts it might *accelerate* wear.
Paul Hunt 2

thanks paul what would you consider to be good oil consumpion for one of these engines mine has done 29,000 from new that was in 1969, it makes no difference how its driven thanks
andy tilney

I agree with Paul, I have never had any problem with the original type of oil seals in either our TD or MGB. the umbrella type seals probably work fine, but if the valve guides/stems are not excessively worn, so do the original seals. Cheers - Dave
David DuBois

Andy-
Unlike the other seals where the goal is zero leakage, the valve stem seal must produce a controlled flow (regulated) leak. It is much more difficult to achieve controlled flow leakage because the margin for error is so small since it is so important for a thin film of oil to remain between the valve stem and guide. However, the amount of oil used to form this film must be strictly controlled. For this reason, do not use the Original Equipment O-ring type valve stem seals (Original Equipment Part # AEK 113). The design of this type of seal only permits it to prevent oil trapped in the valve spring retainer cup from draining down the valve stem and puddling atop the valve, a condition that induces smoking upon startup and leads to heavy, flow-restricting carbon deposits atop the heads of the valves, as well as carbon accumulation on the roofs of the combustion chambers and the crowns of the pistons. This archaic design characteristic is based on the theory that whatever oil goes down the valve stem into the valve guide and from there into the combustion chamber occurs by gravity flow only. This theory disregards the tremendous vacuum forces acting upon the lower end of the intake valve guide and the valve stem, as well as the mist and spray effect that the rapidly reciprocating springs, rocker arms, and pushrods have upon the oil inside of the rocker arm cover. Being made of Nitrile, the Original Equipment O-ring type valve stem seals are prone to failure when operating under thermal conditions above 200° Fahrenheit, a temperature commonly attained in even Original Equipment specification engines when working under a heavy load or in high ambient temperatures.

Instead, install a set of Fel-Pro Teflon-lined valve stem seals that require no modification of the valvetrain components (Fel-Pro stem seal Part # SS 70373 for Chevrolet Vega 4 cylinder 140, ‘86-92 Ford 351 Windsor; also Advanced Performance Technology Part # 70373). These seals have to be slipped over the valve stem using a protective cover before being pressed onto the valve guide with a special tool. Being made of Viton, they are not prone to failure until thermal conditions rise above 450° Fahrenheit, which is much higher than that which any properly maintained street engine experiences. In addition, these positive guide design valve stem seals do a far superior job by eliminating vacuum loss. As a side benefit of the elimination of this vacuum interference with flow through the ports, the fuel mixture is more stable and can be more accurately metered to a finer degree, thus increasing both power output and fuel economy.
Steve S.

While on the question of valve seals. Do you need them on the exhause valves. I have read that they only install them on intake valves. True/False...

Ray
Ray 1977mgb

I was recomended to fit the "top hat" style seals all round by Summit Motors. I did and they work well and so far no adverse effects on any valves inlet or exhaust. It has eliminated that annoying start up puff of blue smoke.
Stan Best

Ray-
Do not use an oil seal on the exhaust valve guide in a mistaken attempt to reduce oil consumption. High gas pressures within the exhaust port momentarily restrict oil from going down the valve stem to both that induced by mechanical transference resulting from valve stem movement and that by capillary action. As the pulse of hot exhaust gases passes out of the port it leaves a partial vacuum in its wake, ambient pressure within the rocker arm cover then forces oil down the valve stem in order to both lubricate the bore of the valve guide and provide a heat-conducting medium. Thus, the absence of a valve stem seal on the exhaust valve guide will have no practical effect upon oil consumption. The film of oil on the valve stem is an essential part of the cooling of the exhaust valve as it fills the gap between the stem and the bore of the valve guide, acting as a medium for conducting heat out of the valve. Because bronze valve guides have closer operating clearances, valve stem seals are not only unnecessary on the exhaust valve guides, but are actually undesirable as they reduce lubrication of the valve stem, accelerating wear of not only the valve stem and its guide, but also of the seating surfaces as a consequence of attendant misalignment.

However, the opposite is the case where the intake valve is concerned. The low atmospheric pressures in the intake ports draw oil down the stem of the intake valve quite readily, leading to high oil consumption and carbon buildup on the head of the valve and inside the combustion chambers. Additionally, the oil being mixed with the incoming fuel-air mixture consequently interferes with combustion efficiency and actually lowers its octane rating, making preignition a very real risk. Always install the highest quality valve stem seals on intake valve guides.
Steve S.

Ray,

the Abingdon Special Tuning manual stated this and i can only agree with the information given by Paul earlier.
On one of my roadsters i tried it without seals on all the valves and it works well, although the CR is 12.5 : 1 on this engine and it is (sometimes) taken up to 7000 rpm there was not a significant conumption of oil compared with a stock engine in one of the GT's that has just clocked 60K miles within 30 years of use.

I think that the problem is the finish of the work done by the workshop when fitting new valves and bronce guides. You must only accept the smallest tollerances quoted by the workshop manual!

Ralph
Ralph

Ray-
I'm afraid the Ralph has got things reversed as regards the clearances on the valve guides. While bronze valve guides have the ability to run tighter clearances at operating temperatures, they do need to be reamed to a larger Internal Diameter because of their greater rate of expansion. Although this may seem implausible, consider that if the valve guide is standing alone in the air, heating will cause its Internal Diameter to increase. However, if the expansion of the valve guide is constricted by it being in a cylinder head that has a lower coefficient of expansion/contraction than that of the alloy of which the valve guide is composed, as in the case of a manganese silicone bronze valve guide in a ductile cast iron cylinder head, then the Internal Diameter of the valve guide will decrease because the metal has to have some unoccupied volume in which to be displaced by the heat-induced expansion. The Original Equipment intake valve stem diameter was .3422” to .3427”, while the bore of the Original Equipment cast iron intake valve guide was .3442” to .3447”, giving a minimum clearance of .0015”, a nominal clearance of .0020” and a maximum clearance of .0025”. As a general rule of thumb, use a micrometer to measure your valve stems and then use a plug gauge to measure the internal diameter of the valve guide. After installing them into the cylinder head, always ream the bronze valve guides to the maximum clearance specified for that of the cast iron guide (.0025”). This will prevent the valves from sticking. Some shops, out of sheer ignorance or an unwillingness to purchase the correct-size reamer for a job that they rarely do, will ream the guides to the average diameter for a cast iron valve guide, and sticking valves become a problem. Of course, they blame the material that valve guides are made of, never themselves.
Steve S.

Hi everyone

We tend to put soft top hat style seals on all inlet and exhaust guides on Bs for road use. It stops the puff on hot start from the exhaust guides. Plus...when someone with a bottom end problem buys a head from me or takes the carbon off the edge of the piston when fitting ahead, 'blame' doesn't seem to apportion to me if seals are visible! MSX heads are good at pulling oil down the guides if top hat seals aren't fitted and superglued in place...3-400 per pint!

MGCs...no seals...big oil burn, the top hat seals were factory fitted inlet and exhaust. T-types, we run Pinto style stem seals inlet and exhaust. Tuned A series...in in-line use (midget) no seals on exhausts as they can seize when tuned and working hard. Transverse use (Mini) all seals on as oil puddles around the guides.

All the best

Peter
peter burgess

Steve,

once an engine builder told me the same and did the same. The result was a sticking exhaust valve on no. 3 cylinder after a few K miles. New guides and valves were fitted by another workshop, going to close tolerances and this solution has lasted for years now.

Ralph
Ralph

Ok,

Steve says no seals on exhaust.

Peter B says he uses seals on both inlet and exhaust on B's...

Steve help me out. Peter is the Man.....or am I missing something here...

Ray
Ray 1977mgb

Ray. What you are missing is the fact that there are some limits of tolerance when building an engine. This means that there is no absolutely correct method of doing thing. Often, there is more than one way to perform a task and each will work well, although each may also have some minor problems associated with it. Each competent craftsman examines what he wants to do, tries to decide the positives and negatives of what he is going to do, and does the best job he can. One procedure may require slightly different machining or slightly different set up, but both are very close to being the same thing and both, as demonstrated, will work, have worked, and have worked well.

What you are missing is that competent people may disagree--and both can be correct.

Les
Les Bengtson

Ray,

i can understand Peter very well, as he must give a warranty for his work. Even if in doupt i also would do anything that noone could tell me i did not do anything...
Sometimes there is a difference between the decissions of enterprises (such as Peter Burgees competence centre) and the solutions engenners would decide for in their own engines.
Les has explaned this very good, i think.

Ralph

Ralph

Wow,

I am going to be installing a new cylinder head that has 3 angle valve/seats and bronze exhaust guides. It has seals on all the valves, so that is why I askied the question. "Doubt" on which way to go does not make this very easy. Both Steve and Peter are well respected in my books. Just don't know which way to go yet....

Ray

Ray 1977mgb

Ray Les is correct, while there are engines there will be different ways to put them together and most will work. Anyone can only offer what they have found works for them. As for me I have been working on these cars for a living since the TD was new and never had a problem with the OE seals, if fitted correctly. My SC B has bronze guides, OE seals on both IN & EX and oil usage is nil between changes (3K). My feeling is that the later type seals work TO well early in life for our setup but then do not last as well as the OE. Denis
DENIS4

Ray-
Peter is correct about the puff of smoke on starting the engine up from cold. If you have no seals on the exhaust valves, a small amount of oil may be expected to drain out of the valve collars and run down the valve stems while the engine is off. Most of it will puddle atop the closed valves and be burned in the exhaust system. However, if a valve is open, the oil will drip into the combustion chamber and form some carbon on the piston crown when combustion starts. If the engine is permitted to run for a while, the carbon will burn away. However, if the engine is used for short trips and not allowed to reach full operating temperature, then you will be faced with carbon buildup and all of its attendant problems.

On the other hand, what I said about lubrication is correct as well.

Perhaps some clarification on the subject of seals is appropriate at this point. I really should have written "do not use the Original Equipment O-ring type valve stem seals (Original Equipment Part # AEK 113) on the intake valves.", and "Instead, install a set of Fel-Pro Teflon-lined valve stem seals that require no modification of the valvetrain components (Fel-Pro stem seal Part # SS 70373 for Chevrolet Vega 4 cylinder 140, ‘86-92 Ford 351 Windsor; also Advanced Performance Technology Part # 70373) onto the intake valve guides." The O-ring type valve stem seals are appropriate for the exhaust valves.

Sorry about the lack of clarification. Does this make better sense?
Steve S.

Steve,

Thanks.

In the Payen head gasket kit it comes with 8 oil seals. Are these any good to use?

Ray
Ray 1977mgb

Ray-
They should be. To my knowledge, Payen has never sold junk of any kind.
Steve S.

This thread was discussed between 14/10/2007 and 17/10/2007

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