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how does a motorbike starter motor work?
hexxi - 22/6/10 at 07:56 PM

How does a motorbike starter motor work in general? I just opened the left side engine cover of my Rotax V990 (from Aprilia RSV mille), and noticed that the pinion is in permanen contact with the flywheel (ok, there are two gears between).

According to my knowledge, in car engines the pinion of the starter motor moves axially to the flywheel when the engine is started and then returns back. When the engine is running there`s no contact between the starter pinion and the flywheel.

So it seems that the starter motor rotates the whole time with this motorbike engine. Does it make any sence? Or could it be that there`s some sort of clutch inside the starter motor? The motor feels quite heavy when turning the pinion so it`s quite hard to believe.

[Edited on 22/6/10 by hexxi]


MikeCapon - 22/6/10 at 07:59 PM

There's a freewheel system, generally hidden in one of the 'idler' gears. That's it really. Simples.


dinosaurjuice - 22/6/10 at 08:03 PM

its essentially a one way bearing but above a certain rpm the 'rollers' retract out the way completely so no friction. can be a pain to re-assemble...


jase380 - 22/6/10 at 08:04 PM

and if you spin your car and end up going backwards dip your clutch or the starter motor will mostly be fooked


ReMan - 22/6/10 at 08:27 PM

quote:
Originally posted by jase380
and if you spin your car and end up going backwards dip your clutch or the starter motor will mostly be fooked


Almost certainly


NigeEss - 22/6/10 at 11:46 PM

Normally a sprag clutch in the gears.


hexxi - 23/6/10 at 05:11 AM

quote:
Originally posted by MikeCapon
There's a freewheel system, generally hidden in one of the 'idler' gears. That's it really. Simples.


Is this "freewheel system" inside the starter motor itself?


MikeCapon - 23/6/10 at 07:17 AM

quote:
Originally posted by hexxi
quote:
Originally posted by MikeCapon
There's a freewheel system, generally hidden in one of the 'idler' gears. That's it really. Simples.


Is this "freewheel system" inside the starter motor itself?


Here's a piccy. The 'clutch' is a pack of rollers between two rings. In the drive direction they roll up and lock the clutch. In the other direction they act as a bearing. As the diag shows they are not in the starter itself.

HTH
Mike


sprag clutch
sprag clutch