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MG TD TF 1500 - Spark Plug Reach

Hope all are having a great Holiday season!

Just in case there's anyone out there still thinking MG at this time of year, I'd appreciate some info.

In preparing to install a pertronix ignition, I have been investigating plugs, and coil too. I have just discovered I have 1/2" reach Champion L86C plugs in my '53 TD head, and I believe based on engine # and head number, I should be using 3/4" reach plugs.

My head is stamped 168422 on the top right front on the head, and my engine # is 24722. So, by all accounts, and the archives, shouldn't I be using 3/4" reach plugs?

Also, if this is correct, how badly has the cars perfomance been affected by improper reach plugs, if at all?

Thanks

Larry
L Karpman

Hi Larry - Seasons Greetings - it's cold and miserable here, just above freezing point - hope it's warmer with you so you can check your plugs !

Irrespective of model, markings, etc, it's best to check independently - it's so easy. Get a length of thin wire , bend a 1/4" right angle at one end, a wide 'handle' at the other and insert into plug hole. Pull back to one side so right angle hits bottom of hole - put vise grip or pliers up to top of hole, move to side, remove and note depth of hole !

I always use NGK plugs but that's your choice - look up archives for advice.

Good luck, John.
J.C Mitchell

Larry,

If you have been running 1/2" reach plugs in a 3/4" head, it's likely there is carbon build-up in the lowest 1/4" of the plug hole threads. If it has been run that way for a while, there is a chance that the metal has eroded.

Hopefully you will find a 1/2 reach head using John's test.

Good luck!!
Evan
Evan Ford - TD 27621

Larry, when I've done that test in the past with my 1/2" head, the measurement always seems to me to be 5/8", which used to give me pause. I assume that a 3/4" reach would yield something longer, perhaps on the order of 7/8", but I don't know. I just wanted to give you my baseline in case you run into the same issue.

But all may be moot because 168422 is indeed the long reach head. 22952 is the short reach head.

warmly,
dave
Dave Braun

Oh, and about performance? Evan is correct, and if the spark is taking place in the 'well' of the spark plug hole, burning will be less effecient, contributing to carbon build up, less power and incomplete combustion.

dave
Dave Braun

Thanks all. I will do the manual measurement today. Hopefully I can confirm either way.

Cheers

Larry
L Karpman

OK, dumb question. How is the measurement taken? I have the head at the TDC mark lined up, and checking #1 cylinder, I have well over 1 3/4" ?????

Larry
L Karpman

OK, sorry to bother. I was not "feeling" the hooked end catch, so I took a light an confirmed where it did. I have about 7/8 - 1". I don't know what I was thinking about piston position. Too early for me after a very late night I guess :-(( Feel sorta stupid right now.

Larry
L Karpman

This thread was discussed on 24/12/2006

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