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MG TD TF 1500 - TD spark plugs

Well I feel like an idiot. I have owned this 1951 TD since 1977 and I now find I may have been running short reach plugs in it incorrectly. Today I measured the depth of the plug hole with a large nail and a piece of clear plastic hose over it and I find that there is .75 of an inch from the surface of the seat of the plug to where the nail will slip over the end of the plug hole in the head. Does that mean I should have long reach plugs and at some point before my ownership the head was changed? If so what are the choices of plugs to run? The engine number is XPAG/TD/LHX9342.
John Quilter (TD8986)

From Neil Cairns: For the more powerful midget TD Mk2 the engine had its waterways improved to help cooling. Whilst the TD Mk2 had both the new head and block, the normal TD and YB had to use up existing stocks. The new items are termed 'round-hole' blocks or heads, and carry casting numbers for the head of 168422 head and 168421 block. There is no octagon cast into these blocks, as they were also used on the Wolseley 4/44, and have an extra boss for the 4/44 dipstick. This was un-drilled on the M.G. 'oval hole' heads are casting number 22952,
The 22952 uses 1/2" plugs, the other 3/4. Not sure what number for the 3/4- NGK B6ES (the old part number) or something? If you have been using the short plugs for a long time, carbon may be build up on the threads and you may need to use a tap to chase the threads. George
George Butz

Cairns has assembled a great deal of valuable engine information, but I have never heard anywhere else his association of the TD/C with the change from banana to round-hole cooling passages, and not at all convinced that his statements will hold water (sorry).

I have always heard that it was an engineering improvement across the board; I would be very interested to hear the source of Cairns' information. The parts book lists the car changeover number that is NOT a Mark II car.

Sounds as though your car is indeed a 3/4" reach car.

Tom Lange
MGT Repair
t lange

The NGK 3/4" reach plug is their B6ES (BP6ES). Their 1/2" reach plug is their B6HS (BP6HS). Bud
Bud Krueger

The WSM states;
Prior to engine #XPAG/TD@/22735 The standard plug is a Champion L10S.
This is a 1/2" reach plug.
From 22735 the standard plug is a Champion NA8 which is a 3/4" reach plug.

My TD was shipped January of 52. The original engine number was 13155.

Check your engine number (ON THE ENGINE) and your head number.
If the car is not a Mark 2 and your engine # is less than 22735 and you have the original head, you should need 1/2" plugs.



Jim B.
JA Benjamin

Tom, I just intended to quote the block/head casting numbers and didn't read that part. I'm with you- that is not correct info. I'm pretty sure in other writings he explains in detail the block /head change, with nothing mentioned about a MkII. George
George Butz

Tom, check your email. I found the rest of the story in the 'Living with the XPAG" book. The initial statement about the MkII is either paraphrased incorrectly or just taken out of context, or just a mistake. The way I read the whole thing in "Living", he says that at the introduction of the round hole block and head, the MkIIs got both from the beginning. The regular TD's used a combo of round and oval until blocks and lastly oval heads were used up many engines later. George
George Butz

Where do you find the casting number on the head?
John Quilter (TD8986)

Front right corner on top.

Ed
ECS Stanfield

George - thanks for the info. I think I would want to see Cairns' source on that, as I have never seen an unmolested engine with an un-matched block/head combo, out of the perhaps 20 I have seen over the years.

Tom Lange
MGT Repair
t lange

This thread was discussed between 04/09/2013 and 06/09/2013

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