Starter motors - difference between car and bike ones

On topic(ish) I suppose.

I've never thought about this until someone[1] asked me today.

Car ones appear to have an external solenoid, and a gear mechanism to
engage.

Bike ones, don't.

Can someone go into more detail please ?


[1] He is converting a small "pull" start engine to an electric start
(speed boatish I think)

 

Cars also generally have two more wheels.

HTH.

 

Fist fucking frenzy

 

Most bikes use sprag clutches instead of inertia or solenoid systems,
though TBH I don't know why.

You'll also find that at least some motorbike starters spin much
faster and use a planetary gear system to slow the output shaft.

At a wild guess this gives them a higher torque in a smaller package;
at another guess it's probably more efficient, so a smaller battery
can be used.

 

The BMW R bikes have an external solenoid , I assume that most bikes
don't
is probably a size/weight thing.

Steve

 

Guzzi's do.

 

Originally car starters used a simple Bendix gear which uses inertia
to throw the starter cog unto the flywheel against a spring which
disengaged it when the engine started. As engines got bigger this
caused premature wear problems. The solenoid on modern car starters
engages the cog onto the flywheel before the motor turns, reducing
wear.

Bike engines are smaller and easier to turn so the Bendix gear is
still good enough.

 

I can't think of any bike that uses bendix type starters.

 

Just changed one on the scoot, but maybe that does not count.

 

The recent one use Valeo that are also fitted on cars or BM (the rotation
is inverted, the nose is different).
Those older that use Bosch units can be retrofitted with the same Valeo.

The interesting point is that you can find oem parts cheap at car parts
dealers, it is esay to fix them.

 

Automobile starters are rather too long for motorcycle use, and using
a Bendix type engagement gear would result in a lot of metal grit from
the flywheel deposited in the engine oil.

A Bendix type starter is certainly the simplest low tech solution if
you have the space and a toothed flywheel.

Most motorcycles use a compact (short) over-running starter clutch
which automatically *engages* itself everytime the crankshaft STOPS
turning.

That's the exact opposite of what a Bendix drive does.

Examples of over-running clutches are the Sprag type, which looks like
a roller bearing with eccentric-shaped rollers or the ramp and roller
type which has only three cylindrical rollers.

Sprag clutches are always engaging a tiny amount and they wear out the
sprags
as the engine runs. Ramp and roller types only wear the rollers a tiny
bit every time the engine stops.

The rollers dropping onto a sleeve in the clutch is what makes the
"whiz-ching!" sound when you shut off the engine of a motorcycle
equipped with such a clutch

To me, one of the disadvantages of the over-running clutch is that it
sits motionless on a needle bearing or pressure lubricated bushing,
while the crankshaft spins up to 15,000 RPM only millimeters away from
the clutch.

I seem to be the only human being on the planet to recognize the
kamikaze nature of over-running clutches, having had two off them
seize up and stop the crankshaft while I was riding the motorcycles.

The other disadvantage of an over-running clutch occurs when the
design engineer decides to *bury it* in the oily depths of the
transmission, where it gets plenty of oil, but cannot be easily
accessed for maintenance.

Early Hinkley Triumphs and Yamahas designed in the 1980's had buried
starter clutches.

There are a bazillion over-running clutches being used in Japanese,
British and Italian motorcycles with no user complaints.

An engine with a flywheel that doesn't run in engine oil can use the
Bendix type starter.

Harley Davidson and Moto-Guzzi use Bendix type starters.

Interestingly, the starter on my Nissan pickup truck has a Bendix
drive *and* an over-running Sprag clutch to prevent the engine from
backdriving the starter...

What about BMW motorcycles? I CBA to research BMW's...

 

Just about every bike starter I've seen has an external solenoid.

 

Yamaha's XS650 twin certainly did, and I am pretty sure the
XV750/1000/1100 vees did too.

Harleys? Though I've little experience of them.

 

He wasn't asking about the single function power switching solenoid,
you silly ****.

 

Didn't say so, though, did he?

 

More a Bosch/Lucas we always done it that way v's Nippon Denso thing.

 

He communicated his question well enough for even a senile Yank to
understand
what he meant, you daft twat.

 

*Shrug*

Whatever.

 

FT500 - spit!

 

Excellent wheelie machine, but crap at everything else, including
reliability.