A couple of thoughts, The plug recommended for the first 88 on the list must be for motors with an iron head, helpful if it said that. The extended nose plug for the Atlas was probably intended for the original dished pistons , how many Atlas motors still run those??. Most run Commando pistons and would need a Commando plug?.
I'm not sure this plug chart is correct.
G15 fitment lists NGK BP7ES (extended nose type) which cross refers to Bosch W5D and Denso W22EP-U.
Commando fitment lists NGK B7ES which also cross refers to Bosch W5D and Denso W22EP-U
Something perhaps wrong there?
I have the extended nose plugs in my Atlas which is fitted with Commando pistons , The plug earth electrode only just misses the valve by the tinnyist margin. That's checking with the head off. Perhaps I should fit Commando plugs.
NGK list the extended nose spark plug BP7ES for most Commando models in their official application catalogue via the link below:-
Where as the plug chart in Roadholder seems to incorrectly list non extended nose spark plug NGK B7ES for Commando models?
Also the Roadholder plug chart has incorrect cross references from NGK to Bosch and Denso in several application examples, two of which I highlighted in my previous post.
Robert, here is the NGK application for your Atlas which is also an extended nose type plug:-
The chart in Roadholder would appear to agree with this fitment.
With so many mix and match engine rebuilds on our old motorcycles perhaps it's almost impossible to produce a definitive spark plug application list?
... is the recommendation for a short reach plug (in the Edgar Franks book and elsewhere) for my iron head 1952 ES2. The thread length in the head is a good 3/4"+ and a long reach plug works fine with no unpleasant plug/piston contact.
... I 'learned' (probably from Motorcycle Mechanics) that long reach plugs were for alloy heads as the head needed more thread to avoid stripping by overtightening. But I could be wrong!!
But why have the plug points buried down a hole by fitting short reach on mine?
hello better spark plugs for Nortons twins are N9BYC these are better for running on ethanol fuels The Same heat range As N5 for a colder plug you need N7BYC yours anna j