Question: How risky is it to put valve seats into a MkII XPAG head?
I have the head off my MkII XPAG because I am putting in new valves,
guides and seals. Today I took the head, with the valves still
installed, to a NAPA machine shop. The machinist was courteous, honest
(unusual today) and seemed knowledgeable. He said at a minimum four of
my valves needed seats, thus all should be done. How did he determine
that? Four of the valves were slightly recessed below the combustion
chamber surface. He said this was seat wear, not valve wear.
Being a MkII, the larger valves are right up against the wall of the
combustion chamber. Virtually no room for seats. He said "shallow" seats
would have to be installed. He did not have the equipment for this. What
is the difference between "shallow" and "normal" seats?
Furthermore, he said there was no telling how thick the casting was. To
him it appeared relatively thin and said it would indeed be a big gamble
to cut a seat for there was a good chance he might cut through to the
water jacket or hit a pocket of sand introduced during the casting. He
recommended I go to another NAPA machinist 25 miles away in the city.
At the second NAPA, I heard basically the same story. The machinist
there said he could cut into the wall of the combustion chamber in order
to give room for a seat. However, he again raised the alarm about the
possibility of breaking through to the water jacket or hitting a pocket
of sand. He highly recommended that I not proceed with having seats
installed but that I have a normal valve grinding job along with the
installation of new valves, guides and seals. He said recessed valves
would not affect the performance of the engine.
Is this good advice or is it relatively safe to grind seats in an XPAG
head? The previous owner STRONGLY warned me several times to treat the
MkII head with kid gloves, because if someone makes a mess of it, I
would never find a replacement. The MkII is just too rare.
I understand John Twist and some others have installed seats in the
regular TD XPAG head. Has anyone heard of any horror stories of grinding
through to the water jacket, etc. Has anyone heard of problems putting
seats into a MkII head?
For the moment, I am leaning toward no seats. The head is too rare and
the risk too high. However, I would appreciate opinions from
knowledgeable and informed TD owners.
Thanks.
Stu Keen
51 MG TD MkII
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