Does anyone knows if older bikes had to have the little bush fitted to the sparkplugs or could do without? Worked with a friend on his bike today and I found that he had sparkplugs (NGK D7AE) fitted with the original (well they looked like the originals) caps. All very dirty inside and one of the plugs had quite a bit of rust on the tip, but the bike ran OK???
Does anybody has a good tip how to clean these caps on the inside?

Thanks, Rene.

I guess the best way would be to run a tap in the hole to chase the thread.
These caps start to be the 'pain' as nobody provide them with new spark plugs.
IF YOU HAVE SOME SPARE, DON'T TROW THEM IN THE GARBAGE. Soon you will not be able to find them anymore.
This is the price to pay for owning an older bike.... Here in Canada, cars are considered 'vintage' when they are older than 25 years, but we (the government collecting fees) doesn't have any rules for bikes.
No special considerations are given to older bikes when DOT (department of transportation) changes any rules. You have to comply. No grand father clause for bike!

Generally plug caps intended for the screw on plug adaptors need them but can function without them at the expense of performance and risk to the HV side of the electrics because the spark will jump the extra gap but it is not beneficial to do so.

One thing often said when checking ignition spark is to do so with a spare plug in the cap and lay it on the engine. It is worth taking care not to let the ignition lead go open circuit when it is sparking as the voltage build-up can cause flashover on the HV side and lead to potential coil failure or so they say.

Very Good point about the little screw on plug tips they are not supplied nowadays.

Another thing I do every time I service any vehicle whenever I have spark plug caps like the K Bike is pull them off and spray inside the boot with silicone spray and spray the plug. This is primarily to stop the rubber bonding to the porcelain of the plug and also to help prevent rusting inside tha cap. After replacement I give the outside of the cap and leads a spray to help reduce the effect of water as the silicone tends to repel water well.
Regards,
K-BIKE

Mine was fitted with suppressed silicon leads before I purchased it and does not seem to cause any problems but I can't remember if it uses the threaded spark plug caps but I am pretty sure they are still available here at least.

Regards,

Phil

Thanks team, better start looking for spare spark plug adapters then!