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Old and new plugs

Some time ago I had a nice discussion about old English bikes with an old mechanic who restores dynamos and magnets as a hobby. He told me the reason why modern plugs are usually short-lived in old bikes: they are not made with porcelain cores but kind of sintered alu oxide. Very good with modern petrol and oil, but in older bikes when they get contaminated with grease the isolation is gone forever. Can anybody confirm this

Re: Old and new plugs

I don't think that there has been any change in the make up of the insulator. What has happened is that there is no longer any glazing on the insulator. This means if you over fuel the engine the petrol can soak into the material used and short out the spark. This doesn't cause a problem on modern engines with their computer controlled injection systems.

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