How to repair radiator cooling fan.
Posted: Mon Apr 06, 2015 11:15 pm
My cooling fan was seized and made a scraping noise when the fan was rotated by hand, it looked like it was non repairable and I would have to find a replacement. This item was at the bottom of my restoration list since up here in Alberta Canada the temperature in the summer hardly triggers the cooling fan even on the hottest of days. But it would be foolish not to have a working one on my bike. So yesterday I decided to see if I can find out why it had seized up since I was sure it couldn't be from over use. First I took off the fan blade and drilled out 2 small rivets from the surround. Next I used a flat screw driver and pryed the top cover off against the pull of a strong permanent magnet. Inside was a thin flat copper wire rotor running on a pivot in the centre of a circular magnet with carbon brushes on the under side providing electrical contact. The principle is the same as any DC motor but to make the motor flat and compact the design of the rotor is unique and the copper conductors are flat and circular. What I found was rust had developed under the magnet on the rear base plate and had pushed the magnet up and into contact with the rotor there by causing it to seize. So I removed the magnet and cleaned the base plate, reseat the magnet, lubricate the pivot pin and reassembled the fan. Tested it and it ran like new, very powerful with lots of force. 
