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MG TD TF 1500 - Spark Plug Advice

Hi. Have owned my 1953 TD since March this year and have nearly completed an overhaul of the engine, brought about by a cam follower failing.

On strip down I discovered that it has a skimmed (oval hole) cylinder head and large valves. The compression ratio is 9.27:1.

During the engine rebuild I have fitted a Brown and Gammonds cross drilled Fast Road Cam.

The original carb mixture settings seem correct and the existing spark plugs were NGK BP6HS, but when checked were always black.

Should I be considering fitting hotter running plugs, NGK BP5HS for example?





John Winzer

Hi John, 9.2:1 is just about the compression ratio obtained from removing .100" from the head. NGK plugs with an H have a 0.5" reach. I would expect that you would be using BP6ES plugs (.75" reach). Bud
Bud Krueger

Hi Bud. Thanks for your prompt reply. I can confirm that the head fitted on this engine is an oval hole type and takes the 0.5" short reach plugs.
I am just wondering if I should be fitting grade 5 plugs rather than 6's. Regards.
John Winzer

You could try 5's but 6's should be ok with that compression ratio etc
Having fitted a fast road cam suggests you drive sportingly so 6's would be the normal choice
I would respectfully suggest that your mixture is running rich if the plugs are black, maybe a sticking choke linkage or similar
Are you pulling the plugs out after a run out the road
William Revit

I have a 9.3:1 compresion engine. i've been running 3 grades :
B6HS
Cooler L82C
and cooler L78C

I finaly choose the L78C.
In very sunny summer days,(south of france) I still had auto ignition with the L82C when stopping the engine.

Laurent.



LC Laurent31

Many thanks for your comments. William, I will certainly check the mixture setting again when I get the engine running, also try to establish what needles have been fitted in the carbs.
Laurent, a good result after your trials, thank you.
John Winzer

Don't forget there could be differences in petrol available in Devon and South of France.

For general use rather than instant plug colouring, over here at least, the higher octane petrols can also have more cleaning in their additive package.

Embarrassingly for me Willy recently diagnosed part of my blacking plugs from a photo I put up as the debris on my air filters (bl**dy careless neighbour cutting breezeblocks).
Nigel Atkins

Good point Nigel. I have been using 95 octane up to now.
John Winzer

John,
I was thinking there could be other differences in the makeup of the petrols for the area and weather, plus (dare I mention it) ethanol content.

I always used to use Tesco Momentum99 for its cleaning package as my car was set on 95 octane. Then I suggested an additive to a N.I. B owner, it worked out as 6p a litre if bought at full price. My wife pointed out that I normally paid 10-12p a litre extra for Tesco 99 or Shell 99 - so I thought I'd give a bottle a try and am pleased with it plus it means I can put in 95 octane at a cost saving and not worry about finding a garage that sells 99.

The additive gave my plugs a distinctive deep or light salmon colouring when I had the mixture far too rich and too rich.

I know many go with Castrol but I preferred a UK/English blender -
Millers VSPe Power Plus

"USER BENEFITS:
. Endorsed by the FBHVC as a fuel treatment for protection against corrosion in metals
. Octane enhancement of up to 2 octane numbers (20 points) dependent on fuel quality
. Prevents valve seat recession when used with unhardened valve seats
. Prevents detonation, hot spots & running on
. Prevents fuel system corrosion and helps protect components
. Combats the adverse effects of ethanol in fuel (up to E10)
. Carburettor anti-icing formula
. Contains anti oxidant to improve fuel life"

https://www.millersoils-shop.co.uk/vspe-power-plus-multishot

£23 from Wilco Direct - https://www.wilcodirect.co.uk/product/fuel-treatments/vsp-epower-plus-500ml-mc-7917kb/MC-7917KB
Nigel Atkins

Thank you for that info Nigel.
Hadn't considered a fuel additive as my TD has been fitted with hard seats and runs fine on unleaded (albeit with black plugs!)

It looks to be beneficial on several counts. I will start using it.
John Winzer

I've been very pleased with it, it seemed to have the car running smoothly but of course I could be fooling myself with a type of placebo effect.

I've never considered regularly using an additive at each fill because of the hassle but as the fill up are less frequent now I've got used to it and carrying a little measuring cup in the boot as spirited driving has the Millers bottle often fallen over in the boot overfilling the 25ml reservoir of the bottle.

I've hardened seats too and have never worried about 'fanol or octane as my car is set up to run on 95 (every couple of years it goes on Peter's rollers) but I think Millers might have helped with a slight turn-off engine run-on when the weather is very hot and engine is hot with electric cooling fan running so the Millers might be doing something there at least.

It'd be interesting to hear how someone else finds it in a medium or long term test - I've still not finished the bottle as my use of the car has been limited even before Covid.

BTW - my black plugs was from an intermittent sticking jet on one carb when the choke was used even fast idle setting, the intermittent really threw me (and it was debris in the air filters and me not doing a good job setting the carbs).

Good luck with yours.

Nigel Atkins

Many thanks Nigel.
John Winzer

This thread was discussed between 24/11/2020 and 28/11/2020

MG TD TF 1500 index

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