Lagondaforum

Subject: Suitable Spark Plugs for 16/80?

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My car is fitted with NGK AB6 's but over the weekend I undertook some Lagonda motoring and suffered with oiled-up plugs. Admittedly this was once, after spending 20 mins in a traffic jam in Farnham however it got me wondering if a different plug would cure this? e.g. would a plug that runs hotter be likely to "burn off" any fouling? Or, is there no cure, it's an 83 year old engine and one has to accept it? I'd be interested in your experiences.

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Subject: Re: Suitable Spark Plugs for 16/80?

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Bought half a dozen NGK AB6 's I assume they are correct, if there's an alternative plug that may be less prone to oiling up let me know

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Subject: Re: Suitable Spark Plugs for 16/80?

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Many years back I was advised to always tune the carburettors on the rich side and in my experience this will occasionally give sooted plugs when left ticking over or stuck in traffic which can give a misfire but should clear once on the move

I tried several different heat range plugs on my 2 Litre and found little difference so stuck with the generally used type

If you found it was actually wet oil fouling then that may be something different..but my guess is it was sooting

Rgds
Mark

Subject: Re: Suitable Spark Plugs for 16/80?

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Thanks Mark, I will see how I get on with some new NGK AB6 's - as you say it was more heavy soot than oil.

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Subject: Re: Suitable Spark Plugs for 16/80?

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You may even find 6 is too "hard" with modern fuels for ordinary driving.
It seems that we can use much softer plugs than previously due to the volatility of modern fuels.
Try 5s and if it doesnt misfire at the top end you would be ok.
I have a friend who is using 4s in a 319 BMW (1936) and he drives it very hard indeed ! He says they are fine !
In my experience NGKs are very good and I would stick to those.

Subject: Re: Suitable Spark Plugs for 16/80?

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Editing thi spost because I understan what Bill is saying now. My understanding is that the 5 is hotter and the 7 is colder. I would have thought that a colder plug would be more prone to sooting. However I am here to learn so am I right in thinking your suggestion is to use a slightly hotter plug?

Thanks Rich...

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Subject: Re: Suitable Spark Plugs for 16/80?

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Hello Richard,

I used to run on the NGK AB6 plugs and they are great but at slow running they do/will foul up.
Last year when driving through Spain (hottest weather there in 40 years – 46 degrees in Toledo) I switched to the NGK 7811/BP6ES plug.
It’s a modern plug so you need an adapter for the thread which I think is good because once the adapters are in place you are screwing into the adapter and not your 80+ year old cylinder head.

Anyway, in a nutshell the performance with this plug is slightly better than the AB6 and they don’t fowl up as easily at lower speeds.

Now that my carbs are correctly tuned (with modern fuel in mind) I have been running on these plugs and they are always a light biscuit brown/whitish colour (apparently whitish is best with modern fuel).

Give them a try, you will not be disappointed (Green Spark Plug Co for best price) and if you don’t like them (but you will) I’ll take them off your hands.

Best Regards
Chris

Subject: Re: Suitable Spark Plugs for 16/80?

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I forgot to mention that I find either the NGK AB6 or the NGK 7811/BP6ES are best when gaped at 18 thou.

Subject: Re: Suitable Spark Plugs for 16/80?

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Rich, I tend to only think in terms of "hard" and "soft" so cant be exactly certain about cold and hot. Someone else will put us straight I am sure!
A hard plug ie a 7, 8 or 9 in NGK terms would be used in my experience on a higher performance engine. For instance when we ran a 2.8 Hart engine on about 12:1 compression ratio we used NGK 8s.
If your engine is fouling either from too rich mixture or oil at lower engine speeds then I would tend to go to a softer plug - more like 5 or even 4. I use NGK 6 on my 4.5 engine and have been thinking of trying 5s with this horrible modern fuel.
In my experience the Green Spark Plug Co are not only reasonably priced but also extremely helpful and knowledgeable.

Subject: Re: Suitable Spark Plugs for 16/80?

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Thanks for all your help everyone. I had already ordered a set of AB6's but will now also order a set of AB5's and see how I get on. As you say I've been reading about plug gaps and didn't realise there's so much to learn. With a magneto you get a weaker spark at slower speeds because the mag isn't producing as much current so a wider gap tends spark erratically at idle speed. A coil ignition is the opposite because at slow speed it gets longer to build up the current so it tends to miss a spark high speeds because the coil is being asked to discharge more frequently. All good fun!

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