Spark plug heat range

Andy

I spent far to much time researching the correct plug for my 1938 CS1 (slightly lower compression than an Inter.)as I wanted a correct period Lodge (good quality plugs) to match the rest of my restoration.

Lots of different head types around this period ,18mm plugs, long & short reach 14mm, cast iron or alloy.If it is any help, if you can tell me what size & lenght plug you need, and if cast or alloy head, I can tell you what the original recommendation is, with a cross reference to a modern make likeNGK if you need it. No mention anywhere on a different plug for running in, unless you have much higher than std. compression.

Stu Rogers' suggestion for Champion plugs is to 'throw them in the hedge'!

Magneto's do not like plugs or caps with resistors or suppressors.

I read somewhere that Champion changed the heat range at some time so a current number is not the same range as the orriginal although the numbers match.

I have a B7ES in my Rudge TT replica, but am thinking of going to a B8ES once it starts to get some serious use. Similar performance bikes, similar heat range plugs perhaps? Gordon.

I expect you are well aware of it ,watch out for piston siezure ,plenty of clearance needed, modern machine shops often get it wrong with Rudges.

This one had been in storage for over 40 years when I got it - still running on pre-modern clearances!

Andy

Gordon has got it spot on - NGK B7ES, or Lodge 2HLN in old money! Stu Rogers also confirmed this.