Lagondaforum

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

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If you google 'NGK spark plug decoder' and then look at google images you should find the table that compares heat ranges of NGK plugs with other makes of spark plug.

For NGK the higher the number the colder the plug, lower the number the hotter the plug

Hope this helps
Mark

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

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Searching for something else, I just came across a page I copied from one of my brother's Alvis club magazines, giving a comparison of suitable plugs available in the 1990s. This states "Worn engines will require a plug one stage warmer to burn the oil off the electrodes."
Cold to hot for then available 18mm NGK plugs is:
A8 - A7 - - - AB6 - AB2. So that indicates your choice would be AB2. If you wanted to try a plug between AB6 and AB2, your only choice is the Champion D21.
Hope this helps. But don't overlook that that oil indicates that something is getting worn and will need attention in the future. Changing the plugs might eradicate the symptom, but it won't be a cure!
Laurence

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

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Thanks Laurence, indeed from my various Googlings I was coming to the conclusion that NGK AB's 5,4 & 3 don't exist and I've not yet had anyone say they use an AB2. Perhaps it's too hot?

As you say I am sure that the engine will need looking at at some time; valve guides & rings would be the obvious wear points but I know from my other cars that if you replace rings you may as well replace the pistons and rebore the cylinders. And if you do that you may as well regrind the crank and fit new bearings. As for the valve guides well that's new valves & springs too... how much is an engine rebuild?

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

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Not necessarily, from that comparison, other manufacturers make hotter plugs than the AB2, and there is only one gap between the AB6 and AB2...and the only plug in that heat range is the Champion one mentioned.

Difficult, but you really need to establish if it's rings or valve guides. New rings and a light hone certainly worked for my 205CTi, but metallurgy is better today, and our old engines wear more quickly than their modern counterparts.
Whatever it doesn't sound like this is an everyday problem, so I think you can kick the ball down the line a bit. Incidentally, I was reading up on Scintilla magnetos today, and oiling up of plugs can result if you have fitted suppressors (resistors) or modern resistance core leads...all a big no-no with magnetos.

Laurence

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

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Even on coil ignition engines I think you will find that suppressed leads or plugs (R in the identity usually) will lower the intensity of the spark and should be avoided. That is unless of course you value your relationships with neighbours or family who enjoy watching television !

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

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I've not got suppressed leads :-)

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

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Hi,
Do a quick compression test.
If you are getting 90 + on each plug then there is nothing wrong with your engine.
It may just be that your carbs are too rich.
Just my pennies worth.
Best Regards
Chris

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

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Just to clarify my earlier post on 18th August and Laurence's above. Yes it seems to be correct that with NGK there is nothing between 2 and 6 for 18mm plugs. I was not aware of this.
I have also checked with the friend I mentioned above who has the pre war BMW. He is in fact using NGK 4 not 5 ! He is using 14mm plugs with an insert not 18mm. He is doing about 50 miles to a pint of oil (burnt not leaked) and does not have a misfire !
He drives very hard !
I think that with modern fuels we can probably use softer plugs than we thought we could !

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

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Just to add to this thread, it's probably worth pulling the engine out during the winter and checking it over. New rings would be useful but above all get new steel rods and shell bearings if these have not yet been fitted. I'm sure BG will do this for you if you do not have the facilities to do it yourself.

In the mean time, let the engine rev nicely to burn off any oil and note H81's advice regarding getting the carbs right. Above all, have fun getting the engine good and hot on a decent run.

M34

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

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I forgot to say that these engines are well understood by Gosnays (http://www.gosnays.co.uk/acatalog/) and if you see Adrian he should give you a price for the machining. He keeps new rods in stock. H81 and I both used him and are happy. They do not assemble engines themselves.

M34