Starter question (engaging)

When a starter spins without engaging with a low battery but
engages normally when the battery's well charged, what if anything,
is likely to need work or checking ? (Battery checks out OK,
plenty of current to crank once it's engaged).

Solenoid ? Voltage drop to the solenoid ? Gear teeth ? Throwout
mechanism ? bearings ?

Thanks

 

Not the solenoid or the voltage drop to the solenoid as long as the
starter is spinning. Engagement is controlled independantly, and my
guess would be the starter clutch...just a guess though.

 

Are you even talking about a motorcycle?

Motorcycles that have a solenoid-operated Bendix drive are rather
uncommon. Harley Davidson comes to mind. What about BMW and Moto Guzzi?

Japamese motorcycles normally turn the crankshaft without needing to
transmit power through the clutch.

The Frankenstein-designed one-way starter clutch automatically drops
its cylindrical rollers onto a sleeve on the end of the crankshaft.
That's the whiz-ching! sound you hear as the engine stops. Also, the
starter probably gets back-driven part of a turn.

It's possible for those rollers to slip I suppose.

Starter clutches of that type are often bolted to the back of the
alternator rotor.

One time the internal taper of my alternator rotor wore out after
constant abuse of the loud handle loosened up the nut holding the rotor
onto the crankshaft. The starter turned without rotating the engine
when the battery was low.

When the battery was fully charged, the alternator rotor seemed to have
enough friction
to turn the crankshaft. The starter sounded strange as it spun up to
higher than normal RPM, then it would slow down as it began to actually
crank the motor.

 

BMW, running a Bosch starter. Guzzis are very similar.

 

Airhead BMW running a Bosch starter. Very similar to an automotive
unit.

 

It's definitely affected by battery charge. Works fine if the
battery's well charged. Got myself into trouble letting
it idle for a while with the heated grips on. I believe there's
and engagement coil and a holding coil in the solenoid, and
my bet would be that one of these was affected by low voltage.

I could be wrong, but I'd thought the solenoid was operated
by the control circuit while the motor was spun by the
battery circuit. I'll probably check for voltage drop just
because it's an easy test to make.

 

Could be that the Bendix shaft needs greasing. Is there a maintenance
item like that in the BMW shop manual?

 

Thanks for some excellent advice. Even at BMW prices
a spring ought to be pretty cheap, as are the rebuild kits.
The starter was sold to me as rebuilt a few years back, so it's
very possible that it might have an oddball spring in there.

Plan B would be to upgrade the whole charging system
from 280 to 400 or 800 watts to avoid the low voltage
problem in the first place.

Regards

Rob Kleinschmidt

 

Greasing the Bendix sounds like a good idea.

Worst case, $100 would just about cover a Bendix, solenoid,
bushings, brushes, brush springs and starter relay.

Only thing I haven't tracked down yet is the ambition.

 

I think you will find ambition right after being pissed off enough about
it to where it won't work much anymore and right before if i don't do it
soon, I am gonna have to eventually.

Fwed

 

Put the rebuild kit on order today from euromotoelectrics.
They suggested perhaps a new solenoid or better yet
their 400 watt permanent magnet charging system.
There are three different guys offering upgrades, each
at about $1 a watt, but I think I'll hold off a little on that one.

I figure I'll start with the rebuild kit, which includes
brush springs. Any reasonable way to test the solenoid
that you can think of ?

Thanks again

Rob

 

Turned out to be the solenoid. When I pulled it off the starter, there
was a whole lot of mechanical resistance right at the point where
it had made an electrical connection but hadn't fully pulled in.
Over a day or two, it had gotten sticky even at normal battery
voltages.

Got a solenoid from euromotoelectrics.com (recommended)
along with a rebuild kit. When I pulled the starter apart though
bearings and brushes were in near new condition so the rebuild
kit gets stashed for later. The starter got a lube with Bosch
silicon grease and went back together as is.

The new solenoid shows a little lower resistance than the old one,
travels freely and starts the bike easily even with the battery a
little
low.

Thanks to all who offered advice.