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MG TD TF 1500 - Spark Plug

My 1952 MGTD MkII is always fouling spark plugs and I wonder if they are the wrong size. I tried measuring the cylinder opening with both a 1/2" and 3/4" wire hook, but it isn't definitive. Both 14mm and 19mm thread plugs were used in the TDs.

Here are some specs. I hope someone can tell me which length spark plug I should be using.

Build Date: 1952/May
Engine No. XPAG/TD3 22096
Car: TDc22096)
Block casting: 168422

Thank you!
Cary Gersh

This thread might help

Enter this number in the Archive search for spark plug length info

201709131833131929
Christopher Couper

Your suggestion to check the archive was very helpful. From what i can gather, my engine would use the 3/4-inch plugs. Thanks very much!
Cary Gersh

There appears to be an error with the information supplied. Both the chassis number and the engine number are the same; 22096. This is incorrect, so one of them must be wrong.
However, according to the MG production records, chassis TD/C21673 did receive engine XPAG/TD3/22096 in 1952, but it was on the 5th November 1952, not in May. The MG production records show the date in the logical UK format.
Also, 168422 is the cylinder head casting number, the block casting number should be 168421. The 168422 head had a thread length of ¾” for the spark plugs, which had M14 threads, as did all T type cylinder heads.
R WILSON

I really appreciate the time you spent sussing this out for me. I've ordered the 3/4-inch spark plugs with full confidence (now) that they are the correct ones.

Many, many thanks!
Cary Gersh

Just a thought, but chassis number TD/C21673 does not appear in the Merson TD list.
If TD/C21673 is your chassis number, you might consider sending an email to Bud@Ttalk.info, so that he can update the list.
R WILSON

Cary, if that doesn't resolve your problem you could try fitting a slightly hotter plug. I fitted an NGK BP5ES (instead of the BP6ES) which made a useful improvement.
Pete
P Willows

Just a note, if your heads require 3/4 inch plugs and you have been running 1/2 inch plugs, make sure you clean all the threads very well before installing the longer plugs. You'll thank yourself when the next plug change is due. I always coat the threads with never seize for a thread lubricant also. PJ
PJ Jennings

This thread was discussed between 22/03/2023 and 25/03/2023

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