Topic: Speedometer trouble

[janwic]

Hi,

I own a worn down, ill-running CB500K0, and still I prefer it to my other bike, a perfect, fault-free Valkyrie. I guess Pirsig's book from the 70's, about the art of maintaining an old bike, can explain my preferences. After having realized that old is better than new, I have decided to trade my Valk for a '79 Yamaha XS1100 and a '83 Kawasaki Z1100 Spectre, both with a lot of interesting faults. I have not informed my wife of this yet, if I never post here again you'll know she took it bad.

To the topic. It has an interesting fault that I fail to solve on my own. The speedo behaves erratically at speeds above 40mph, it suddenly jumps up to the higher end of the scale and back. This does not happen at lower speeds. I thought this problem was due to dirt being caught in the magneto-torsion-clutch thingy which converts revolutions to angle within the speedo, by physically engaging the needle drive and sending it into to the interesting speed range. Thanks to the autopsy instructions in the tech forum, getting the speedo in pieces was easy, and dirt can be ruled out. When I connect the speedo cable to a power drill, the speedo works just fine (and wow what an impressive acceleration it can display! No man has ever seen an CB500 accelerate like that without a power drill). Does anybody have a clue of the cause? Something in the wheel hub? Wrong grease somewhere? Vibrations during driving which the power drill does not induce? Any advice is much appreciated.

/Jan

[Raul CB750K1]

The inner wire must be well greased, but leave the last inches in the speedo side clean to avoid grease going in. Another cause for erratic behaviour is tight angles. The drive must be laid loose, with fluent lines and wide angles. If somebody installed a longer drive it is possible that it is kinked somewhere. Check it out.


Raul

[janwic]

Raul, thanks for the tip. I did grease the wire, but the problem is still there.

However, a thread in another SOHC forum informed me that there is a guy in the countryside of Sweden who restores speedos, so I gave him a call. He told me that these symptoms usually occur when the seating around the bearing, which carries the magnet converter (or whatever that would be in English), gets worn - eventually vibrations will make the bearing misalign enough for the magnet to be touched by the cup shaped wheel, and this moment of physical contact is enough to send the needle across the scale. And, of course he can fix such problems, a restored speedo is about 120 Euros. If anyone else suffer from this, the URL for his Swedish web site is http://www.instrumentjige.se/.