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MG Car Repair/XPAG tappets and valve seals

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Question
Hello Barrie,
I've recently had my XPAG engine (TC) rebuilt to run on lead-free petrol. When I start the engine the tappets are very noisy for about half a minute before becoming quieter. I checked the tappet settings which seemed ok (.019) but I noticed there was no pool of oil in the valve cap. A further check (by poking a piece of wire between the collets) I descovered there is no rubber sealing ring under the collets and the oil is draining away. I started the engine with the rocker cover off and there is no oil at the tappets until the pressure builds up and oil flows from the top of the rocker down towards the tip and into the valve cap. The oil seals for the valves/guides are the modern type fitted on top of the valve guides.
 I've looked at all the forums on this subject and the debate is always "which to use - original O-ring-type seals or modern umbrella-type seals".  The consensus seems to be one OR the other, not both. The original design used the rubber ring (in the right place, in the valve cap under the collets) to retain oil at the tappets and the deep shroud to stop too much oil being splashed onto the valve stem.
 Is it now ok to do without the pool of oil at the tappets on start up or are we generally missing the point of the original design?

Answer
Hi Joe.  What an excellent question.  

The original O ring served two purposes.  It stopped oil dribbling down the valve stem and it retained oil in the valve cap where it acted as a reservoir to lubricate the tip of each rocker.  

If you have fitted modern stem seals than you must NOT use the shrouds because they will destroy the new seals.  However, I believe the O rings should be retained because otherwise the valve tips will be dry whenever the engine is started up, leading to rapid wear of the rocker tips and mushrooming of the valve stems.

The clattering noise you can hear is probably dry rockers, but it could also be dry cam followers.  I suggest you run the engine without the rocker cover and check that oil is reaching the top of the engine. Oil should spurt out of the hole on the top of each rocker. If not, you have a problem.

o It is possible to assemble the rocker pillars incorrectly so the rear pillar is blocking the oil supply hole in the head.

o It is possible to assemble the rocker shaft incorrectly so the 8 lubrication holes do not line up with the holes in the rocker bushes.  

o It is also possible that new rockers have not been drilled correctly after re-bushing.

Let me know what you find

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Barrie Jones

Expertise

MG Sports Cars from 1949 to 1980 - Including MGB, MGBGT V8, TF1500, TF, TD and modern Midgets. I also specialise in SU carburettors, Lucas wiring, suspension, steering & brakes.

Experience

I have owned my 1955 TF1500 since 1966. Technical specialist for the TD and TF with the MG Car Club T Register. Also owned 20 MGBs and currently own an MGBGT V8. Written 3 books on MGs and produced a DVD on how to strip and rebuild the TD/TF gearbox.

Organizations
MG Car Club.

Publications
Barrie's Notes on the 1953-55 MG TF (author). /=====/ Barrie's Notes on the MGB (author). /=====/ Barrie's Notes on the MGB GT V8 (author). /=====/ The Essential Buyer's Guide to the MG TD, TF and TF1500. (author)

Education/Credentials
M Phil, C Eng, BSc (Eng).

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