Bike: 1979

Issue: voltage drop on output from starter selenoid to starter.

Symptoms:

Selenoid sitting on bench
Ground selenoid case to ground of battery
Long post of selenoid going to positive of battery.

Test voltage at long post with meter have @ 13volts.

Put 12volts to terminal to energise selenoid.

Check voltage at short terminal of selenoid.
Only reading about 10.3 volts

When connect starter to this setup, getting same voltage readings.
Starter barely spins.
I believe the voltage drop is the problem.

If I run positive of battery direct to starter, starter spins fine.

Tried another selenoid with same results.
Granted this is an old selenoid, so it could already have a problem.

I have not tried another battery at this time.

Does anyone have any prior knowledge with this problem?

Any suggestions?

 

I would dismantle the solenoid, clean and inspect the inner workings.

When the plunger activates it moves a large washer [copper in the good, OEM solenoids, steel in the less good new aftermarket ones] to make contact with both of the studs. The washer and also the studs get physically worn out. You can buy a kit which has new parts including the plastic cap, both studs and the washer/plunger assembly.

The most tedious part of the process is putting it back together. There are rectangular parts that must fit into rectangular holes in the plastic cap, the assembly is under spring pressure, and you have a couple of small wires that must not contact internal moving parts. Just the usual IronHead tediousness, take your time with it.

What i have done a couple of times is, instead of replacing the studs [one of which requires a bit of soldering], i rotate the stud so the good side is being used.

If you dismantle/clean and inspect before buying the kit you may well find that you do not need the kit.

If it is all rusty and cruddy inside [likely] i clean it with spray can electrical contacts cleaner.

 

I recommend cleaning the contact washer in the solenoid but remember a starter draws a lot of voltage when cranking and 10v while cranking sounds normal.

 

Not the same but the same principals.