On Sat, 15 Nov 97 23:11:40 -0500 Larry Macy
<macy@bblmail.psycha.upenn.edu> writes:
>IF you get smoke when you back out of the throttle( High vacuum) is that
indicative of valve guides?
It could be bad guides, bad rings, of an overly rich fuel mixture at the
carbs. If you have good compression, badly worn guides are a prime
suspect.
>Do MG engines use valve seals?
Yes and no. They have something called valve seals, and they don't seal.
The stock MG valve seals are just small o-rings that ride on the valve
stem just above the valve guide. The intent is to throw off excess oil
but to allow a little oil down the guides to oil the valve stems. When
the guides get worn sloppy, lots of oil can get past and get into the
intake or exhaust.
Oil down the intake guide gets into the cylinder, causes smoking when it
burns, and carbons up the intake valve. This condition is aggravated by
the fact that the intake port is under vacuum which literally sucks the
oil down the guide. If you pour a quart of oil quickly into the engine
when it is running, the oil can overrun the top of the valve guides, and
you may get a rather surprising cloud of smoke out of the tail pipe.
Oil down the exhaust guide can get blown out the tail pipe and appear as
droplets of oil on the windscreen of the following car. I have
experienced this phenomenon from the following car while the car ahead
was going through a quart of oil every 50 miles.
Without pulling the cylinder head for a full valve job, the installation
of umbrella seals can stop the oil flow down the guides. An umbrella
seal is an upside down rubber cup that fits over the top of the valve
guide and constricts around the valve stem to stop the oil flow down the
guide. This is not a miracle fix. If the guides are badly worn the
valve stems still wobble around a lot in operation, and the new seals
will fail in short order.
I believe these seals are Victor Umbrella Seals, 8B45613 for the MG TD,
and 8B45404 for the MGA, MGB, and MG Midget. I have always repaired the
guides or have used a different system of valve seals, have not used
these particular seals myself, so cannot personally verify the
correctness of the part numbers. Others can, especially John Twist has
used these parts and has previously publicized the numbers.
Barney Gaylord
1958 MGA with an attitude
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