Model 18 Crank pin

Hello,

I attached Alpha's catalog page for Norton big ends. Their listing suggests a N1 for your year machine. N3 looks like later year? Good Luck

http://www.alpha-bearings.com/Big%20end%20Catalogue/Norton-600.htm

I see a note at top of listing as to the difference being shank diameter between the two numbers.

Hi John,

Your 1930 Model 18 should have a 1"crank-pin. This was used in subsequent engines until part way through 1933 when I believe there was a manufacturing problem and this was increased to 1.02" (20 thou oversize). All these big-end assemblies remained the same for the next 30 years until production stopped. This is the difference between the Alpha N1 and N3.

I think your bearing dates from the 1970s/80s as this type of protective covering was used then, although it could be later. You should be able to or get your flywheel holes enlarged to the later size but this needs to be done to the upmost accuracy. The hole is parallel bored and the crankpin has a very slight taper and this needs to start to bind when no more than a third of it's length is pushed into the flywheel at normal room temperature. Ideally this should bemachined with both the flywheels locked together or to use a mandrel to set-up each flywheel andmight be best to take to an engineer who understands the application and tolerance required. When you fit the new pin you could try warming up the wheels to 100c so you don't damage the new surface.

Regards, Richard.