Sat Oct 22 01:47:52 SAST 2016

Solenoid might be the culprit

By unknown | Jul 01, 2009 | COMMENTS [ 0 ]

MY girlfriend and I really appreciate the mechanical insights we gain from your weekly column.

MY girlfriend and I really appreciate the mechanical insights we gain from your weekly column.

We have a 1981 Kawasaki 440 LTD motorcycle that has had a hard life but is still providing much-needed transport.

It is showing strange behaviour. When the makeshift starter button on the handlebar is pressed the only thing that happens is a single, loud click from the starter solenoid. When the button is released, there's another click.

We have confirmed that the clicks come from the solenoid, mounted on a frame rail, by putting a hand on the solenoid and feeling it "kick". If we bridge the two large contacts on the solenoid with a screwdriver, the starter motor will cut in, swinging the engine lustily. But this trick is difficult o for one person to do so we often resort to push-starting the bike. Your suggestions as to how we can get a functional starter switch back will be highly appreciated.

John and Ulla


John and Ulla, from what you say there can be little doubt that the problem lies with the solenoid or at the heavy-duty contact where the thick wire going to the starter motor is attached to the solenoid.

The fact that the starter swings the engine with gusto when the solenoid is bypassed, rules out a weak battery, a faulty starter motor and bad connections in the rest of the wiring. My first action would be to clean up that contact on the solenoid.

Remove all corrosion and dirt from the terminal as well as from the lug on the wire. Use sandpaper to get the lug shiny. Then spray some de-watering fluid on the connectors and tighten up the connection firmly. If this doesn't restore the normal working of the starter button, remove the solenoid for inspection after first noting which wires go where - a drawing is best.

The heavy wire bringing current to the solenoid from the battery is permanently "live", so it's essential that you isolate the battery by disconnecting its earth cable before doing anything else.

With luck you might be able to open the solenoid housing to see why the switch inside isn't passing current to the starter motor, though it is clearly being pulled closed with a solid click. Perhaps there is corrosion or a build-up of arcing deposits on the contact faces, which you can clean off with fine sandpaper. If the solenoid is so tightly sealed that it cannot be opened without destroying it, you will have to buy a new one. Note the current rating marked on the solenoid and get yourself a heavy-duty relay with the same or higher rating.

The "chattering" of the solenoid is often an indication of a battery that is too weak to keep the switch inside the solenoid closed against the spring . In that case the battery will be my first suspect .

Measuring the voltage across its terminals after it has been fully charged (with a charger ) and then allowed to rest overnight. The next morning the voltage should be around 12,8 volts


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