NGK BP5ES Spark plugs for Cambridge head

[Speedex750]

I agree with the others - you should fit BP5HS - that's what I've got in my finned head and they work well. With them having projecting electrodes watch out for touching the valves. I've got a high lift cam and the head must have been skimmed down in the past - I have to selectively fit the plugs with different thickness washers so the earth electrode runs across the engine between the valves. Put your new plugs in and slowly turn the engine over a few times, if the gaps close up you may have to do the same as me.

Dave