Graham Wilshaw of Startright, Leeds
There is no doubting the fact that a good Norton is a wonderful machine to ride, needing little maintenance to keep it that way. Unfortunately, not all second hand ones are in a good state of health. I have listed the main areas you should look at when thinking of buying one. This method of appraisal holds good for Interpol 2 and Commander; the F1 and F1 Sports are rather more difficult to check because of the lack of a centre stand but they react in the same way with regard to the engine.
Place the bike on level ground, on its centre stand. Start the engine and hold at around 2500 r.p.m. Without sitting on the bike, engage first gear and let out the clutch - BE CAREFUL ! ! Gently use the throttle to simulate drive and overrun listening carefully to the gearbox and repeat for all gears; third is likely to be the noisiest. There is always some noise from a box tested like this but you will be able to tell how worn it is by comparing to top gear which, because of the design is the least likely to be noisy.
Noisy gearbox ? Allow around £75 per pair of gears plus about 15 hours labour, because the engine must be removed before you can get to the gearbox. By the time you have reselected neutral, the temperature gauge should have lifted from the stop and the engine should be ticking over at around 1200 r.p.m.; if this is so then the engine may well be good.
Once the engine is warm (Interpol 2 minimum 100 degrees , Commander 80 degrees, (perhaps you could get the owner to take it for a warm up run) the ignition retard system will be switched on by a temperature sensitive switch. This system operates below 2100 r.p.m. and can provide up to 70 degrees of retard to force the idle speed down to an even 600 r.p.m. This low idle speed will show up any weaknesses in compression or carburation / ignition problems.
Suffice to say, if it ticks over evenly under 1000 r.p.m, it's a good one. If there is no tickover or an ailing one, listen closely to the airbox or airboxes (Commander) to see if there is air blowing past the rotors back into the induction. The noise is like a 'chock chock chock' and would suggest that the surface the rotor runs against has been smeared by excessive heat. To decide which side is bad, remove one plug lead, start the bike on one rotor, see how slow the engine will run without stalling and compare it with the other side. If it won't fire up with one plug lead off then it's pretty bad.
Allow a minimum of £750 for an engine rebuild (maximum probably around £1500). I strongly believe in a special coating of molybdenum on the endplates which can reduce internal friction and increase engine life; cost - under £300 per engine.
I have deliberately kept it simple to make sure you know what you are getting. If you want more or to know more, contact me; better still take a ride out to see me.