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MG TD TF 1500 - Updated Spark Plugs

Spark Plug technology has come a long way since the French designed our XPAG engines in the 1930's. Today, we have spark plugs that seem to last forever.

Is there any benefit to switching to platinum or iridium plugs? I've already got a pertronix system that has made a significant improvement in starting and running cooler.

Should I stick with my tried and true Champion N5C?. I do a fair amount of cruising at highway speeds

Gord Clark
Rockburn, Qu.
Gord Clark

I run platinum plugs in my MGC and I'm probably going to switch back. These old engines don't run as clean as modern ones so for the same reason why I don't run expensive synthetic oil that can theoretically go 10,000 miles between changes, I don't feel the high end plugs offer any real value. Others may disagree.
Steve Simmons

My thinking is that SUs can sometimes run rich, and this can cause a plug to work pretty hard to clear it.

I understand that the platinum and iridium plugs, will fire no matter what. Not often my plugs fluff-up and it sometimes takes a few moments to clear them. Will a platinum or iridium plug be any better?

I believe that platinum and iridium plugs were designed for the quite high compressions of modern engines. That's not something I need.

Gord Clark
Rockburn, Qué.
Gord Clark

I've replaced platinum plugs in the MGC because they were too gunked up to fire, so I wouldn't say they fire no matter what. But I'm not sure if they are better or worse than standard plugs in that situation. I guess I'll know after the next plug change. The engine is high compression, around 10.5:1
Steve Simmons

With the N5C at $1.99 at Advanced Auto Parts using whatever coupon they are offering I think I will stick with them.

After carb rebuild, distributor rebuild the car starts on first try, if it ain’t broke ....

P G Gilvarry

This sums it up pretty well.

Timothy Burchfield

NGK- B6ES might be worth a try
A lot of guys swear by NGK plugs here
The Champions we get here are a bit hit and miss
Actually ,on a basically std XPAG, B5ES would probably be better, a bit warmer than a B6ES and NGK plugs are known for being a bit forgiving in their heat ranges a bit without an issue

With the iridium plugs I believe you are correct in thinking they are built for later engines mostly with high output coils and very large plug gaps to help with the very lean mixtures required now--They have their problems though, there wouldn't be many that get to their scheduled plug replacement time
A prime example is early 4 cylinder Ford Mondeos, the service schedule is up near 80-90000Klm somewhere but 50000 onwards and they start sparking down the outside of the insulators causing missfiring
William Revit

I ran iridium plugs in one of my trucks and didn't notice any difference in performance between them and the stock recommended plugs. Changed them about 60,000 miles and they still looked good, but went back to the recommended plug for that engine. I run N5Cs in the TF, ran different number champs in the 72 B also with no problems. PJ
PJ Jennings

Just thought I'd mention that our engines were NOT designed by the French in the 1930s. Our engines were based on the Morris 1140cc XPJM engine, which was designed in the Design Dept of the Morris Motors Engines Branch factory at Courthouse Green, Coventry - in 1938. It was an overhead valve design, based loosely on the previous MPJM/MPJG OHV 1292cc design, also designed in the above Design Dept. There were two articles in "The Autocar" in 1939 about the design of the Morris XPJM engine, and the articles are available to read on the MGCC T Register website, with access; .
The Courthouse Green factory is not the ex-Hotchkiss factory, which was also in Coventry, and which Morris used, and later bought, to make an engine based on a side valve engine designed in the USA. Production of the side valve engine ceased in the 1920s, and the factory stopped making engines in 1936.

It might be useful to add that the USA designed engine probably had USA threads, although I am not sure what they would have been in 1919 - possibly Whitworth. However, Hotchkiss was a French company, having moved from France to Coventry during WW1, and they used the Systeme Internationale (SI) metric thread system, slightly incorrectly known as "French Metric", for all their threads. Thus all their taps, dies and other thread cutting equipment was set up to produce SI threads, so these were the threads used for the Morris engine. However, the hexagon heads were changed to imperial so that English motor mechanics had spanners that fitted. Morris continued to use the SI metric thread system until about 1956, and the SI metric thread system was replaced by the ISO thread system after WW2 (although not all ISO threads are metric).

This thread was discussed between 07/08/2019 and 15/08/2019

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