Spark plug burnt?

[JeffW]

Hi all

Yesterday I installed new Magnecor leads. With them, I am running the Bosch Red coil and Bosch WR8DC plugs (as installed by Faversham and renewed by me).

Today I was running along beautifully en route to Hampshire when I heard a pop and the engine started misfiring. I nursed it home, clearly only running on 6-7 cylinders.

After testing the new leads and checking for any ripped diaphragms in the carbs (all fine), I took out #1 spark plug to find it basically melted and burnt - see attached.

I then took out all the rest of them and found varying degrees of black burn. A photo of #6 cylinder is also attached.

Does this mean the Magnecors + Bosch Red + Bosch plugs are incompatible? Does the Bosch Red coil pump out more/stronger spark and with the addition of the Magnecors with less resistance mean I am toasting them?

Any ideas?

Thanks
Jeff

[blue 464]

I think there should be a +3 added to your number, check with faversham on tuesday, derek

[JeffW]

I think there should be a +3 added to your number, check with faversham on tuesday, derek

Thanks Derek,but I have the original ones Trevor at Faversham installed and they are the same - no '3'. However when he installed them I had the original coil and standard green leads.

EDIT - Hi Derek - I have the original box I got my set in and at the top it says +3. Sorry, you were right!

Jeff

[Kithmo]

It looks like a carbon build up from excess oil in the cylinder, like the sort of thing you used to get when running two strokes in with extra oil. What's the oil consumption like ?

[bullstarz]

Black plugs dont melt normally as its two different things. If they are the correct plugs and melt it means your mixture and/or timing is well off. Black is either oil or way too much fuel but with a really rich mixture you will not melt the plugs. As the excess fuel keep the combustion temp right down. If the spark was too weak this would also cause the black fowling not a too strong spark.

The plugs wont melt due to the coil/leads as it just a spark and that what the are designed to do. All that will melt plugs is a excessive high temperature in the cylinder.

[JeffW]

Thanks all. I am even more perplexed.

Doesn't burn any oil at all, rarely have to top up. Did a compression test recently and all cylinders were circa 140 except one, which was 90.

Timing set by Faversham recently (June) and the car runs beautifully so don't think the timing is way out.

Guess I will try a Colourtune and see what the mixture is like. May not be a perfect test, but at least I will know if the carbs are roughly set.

Thanks
Jeff

[bullstarz]

Look at this;

https://www.onallcylinders.com/2012/12/20/reading-101-how-to-read-your-spark-plugs/

[JeffW]

I didn't know anything about heat rating for plugs - all online selectors seem to have the NGK BP5E's listed for Stags and I know a lot of people here use them. The diagram on this page show overheated plugs as a result of the wrong plug being chosen:

https://ngk-sparkplugs.co.th/product-knowledge/basic-knowledge/heat-rating/

Mine resemble the overheated one more than the fouled one, as the electrodes are damaged, whereas on the fouled ones they are fine.

The Bosch Red Coil claims to produce a 'hotter' spark. I don't know if that's marketing speak or not!

Jeff

[Goldstar]

Maybe a duff batch of plugs?

[trunt]

+1 on the oil..

you would not always notice oil consumption, especially if it’s only one cylinder. What do the rest look like?

[JeffW]

...and here is a couple of more pictures of one spark plug, either side of the electrode. Oddly on one side it is tan but you can see the tang is damaged from (I assume) heat. On the other side of the plug it is wet and sooty.

[JeffW]

+1 on the oil..

you would not always notice oil consumption, especially if it’s only one cylinder. What do the rest look like?

mostly black, with a couple tan coloured showing a reasonable burn.

[JeffW]

Maybe a duff batch of plugs?

Thanks Paul, but they have been in the car for more than a year with no issues and none of this type of fouling / heat damage when I did the compression test and took all the plugs out. Seems odd that when I switch leads they all of sudden fail after a 2 hour drive.

J

[flying farmer]

That plug is fouled not burnt. When plugs are burnt they go a very white colour.

The other plugs should not be black, they should all be a light tan colour.

I would suspect your mixture is much too rich which is resulting in lowered combustion temperatures, and I would suspect oil contamination on the plug that is pictured as well.

I think the changing of the leads is just a coincidence, this would have happened anyway. If you clean the crap off the plug you will probably find the electrodes are ok. I notice the threads of the plug look quite oily which reinforces the theory it is an oil burning problem.
I don't know anything about Bosch plugs as I tend to use NGK, but I assume that if they are recommended by Faversham they will be the correct heat range. If the mixture is weakened it will probably lift combustion temperatures enough to keep the plugs clean.

Neil

[wilf]

Wonder if these plugs are way out of their nominal "heat range" because they are counterfeit? Lost of counterfeit spark plugs around at the moment, and very difficult to spot them, even for a trader, so good is the finish/print on the carton etc.

I would try a new set of plugs and see what happens.