The 1960 99c has 12v electrics ,RM15 zener and 2 MC cap. Its been charging fine for the last 20 odd years of light use. Over the last few weeks I have not treated the bike with the respect its old age deserves. Its had a hammering,and the vibration at 65/70 is not comfy. Things came loose .Now the charge does not balance .I have checked the Alt leads resistance and all is normal,I'm going to try it with the Zener and Cap disconected. Bit worried I have finished off the main bearings and there could be contact .Any other simple checks I can make?. Later, Using car hl bulb alternator gives bright light as per dynamic test.suspect rectifier ,wiring or ampmeter. How to test rectifier ? ID the output lead but if switch/meter fault then current can't flow anyway?
An RM15 even brand new wil…
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HI Phill, the alternator n…
HI Phill, the alternator normally charges about half way across the scale and the zener cuts in after a few miles as the battery is fully charged.I also run indicators and often ride in the daylight on the pilot so even though its old it must be a good un. I have found a melted spot in the rectifier so we will see if a replacement sorts it out.The vibration does seem a bit much at 60-70,Perhaps i will try faster. It was not balanced for the 650 pistons which along with the possibility of a reversed flywheel would not help. Don't want to re-build till after the classicTT as I have two other bikes to sort as well.At last years TT the Norton kept 2 bikes batteries going and carried around 30 stone , It deserves some attention.
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The rectifier is the weak…
The rectifier is the weak spot, normally failing on the way to the MoT test. Cheap and easy to replace, though I would go for one of the modern solid state regulators and do away with the rectifier and zener diode. To quote one of my tutors, "There are no electrical failures, only mechanical failures".
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You must be psychic Gordon…
You must be psychic Gordon ,very close, went to the MOT on battery power only.Bought 2 recs so I can cary a spare. All my fault, whats left of the brain went back 50 odd years and went for 90 in third,a wonder it did not go bang.Still it feels properly bedded in now.
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Charging now back to norma…
Charging now back to normal, a £3 rectifier fixed it, New one now mounted on ally heat sink plate under tool tray.
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An RM15 even brand new will only chuck out about 60W. You mention 12 volt electrics which suggests you may have a modern headlight bulb of 45/50W, tail light 5W, brake light 18W etc. No wonder you aged alternator is struggling. Retire the poor old thing and go for an RM 19 three wire or RM 21 two wire system. Add an electronic regulator / rectifier and enjoy safer night riding.
If your 99 is seriously vibrating at 60 to 70 mph then it probably is time the bottom end was checked out as well. Time for a major rebuild I think!!!