Bendix Gear

[Bob Bennett]

I have starter problems, 1985 R80 Mono,

It starts ok cold, but most of the time when hot' (ie, riding for an hour and stop for 15 or 30 mins) the starter rotates the engine about half a rev and then just spins not rotating the engine, could the bendix work ok cold but slip when hot?

I have had the starter out three times now and this is all I can think that the problem could be.

All info and response is much appreciated

[Ken in Oklahoma]

I gather that your starter is a Valeo, as opposed to the earlier Bosch starters. I have little experience with Valeo starters, but I'm not going to let that stop me.

The Bendix gear will be thrust into engagement with the flywheel gears by the solenoid (which also makes the high current electrical connection to the starter motor). The gear is either going to be thrown in to positive engagement with the flywheel or it will not, spinning ineffectively. For the engine to turn part of a revolution then stop means that the gear is positively engaged.

So your problem will lie somewhere else. Either the starter motor isn't getting the high current supply it needs or the starter is encountering an abnormal load (such as a dragging starter armature or something worn so badly that an abnormal mechanical friction happens).

You've been working this problem hard (three starter pullings is work). Surely you would have noticed any slop in the bendix mechanism. What I'm wondering about is whether the problem the Valeo is famous for, namely the field windings coming loose from the starter shell, could be the source of the friction. However I don't see how that would be temperature dependent.

Can you tell us what you've done to make sure your battery is good (such as jumping it with a car battery) or what you've done to make sure that your battery cables, positive and negative, are known to have good, bright, high current connections? Have you been inside the solenoid to look around? That's where my thoughts are.



Ken

[Bob Bennett]

Thanks for your reply Ken.
I really should have said that it is a Bosch at the start. Sorry.
I have already checked and all addressed the things that you have mentioned. though the bendix is a little sloppy
on the shaft.
In this Bosch starter there is a one way clutch type mechanisim located in the bendix between the solenoid drive ring and
the drive gear. I think its job is to stop the engine driving the starter motor on occasions. I think my problem could be
that this clutch is sliping in the drive mode and was wondering if anybody has had this problem, maybe knows of a fix,
or indeed can tell me that I'm barking up the wrong tree. Not a lota trees left though.
LOL yes I'm getting rather speedy at pulling and replaceing the starter now.

[Sibbo]

Hi Bob ,let me preface my comment by saying that I know SFA ! That said ,something electrical that works cold but not hot sounds like a tiny break in a wire .Cold ,you have a connection ,hot the wire expands and the break somehow gets bigger .

My 2c worth .

[Rob Frankham]

I'm going to throw a reather scary possibility into the mix here...

As I understand it, the problem is that the starter turns the motor for about half a turn them the starter spins free and the motor stays still.

This is classic for a couple of teeth missing off the ring gear or wear to the ring gear and drive gear... not as unusual as you may think. The drive gear will always tend to hit the ring gear at the same spot and this causes uneven wear on the gear. AFAIK, there is no way to replace the ring gear and a replacement flywheel/clutch carrier is the only way to go.

Sorry, said it was scary

Rob

[Garnet]

Bob, you can have several problems that have symptoms that you describe.

A poor battery, althuogh they usually show their weakness cold rather than hot, but it should be tested.

Poor battery cables or connections. Take some time to read this thread: http://boxerworks.com/forum/viewtopic.php?f=1&t=984

I'll finish this in a bit.

[Garnet]

OK I'm back,

Bosch starters will "drag" when hot when their bushings wear. As well there could be a drive problem, but it is less common.

http://www.euromotoelectrics.com/ and http://www.motoelekt.com/index.html sell replacment parts, starters and Motorrad offers Bocsh rebuilding.

[mattcfish]

I'm going to throw a reather scary possibility into the mix here...

As I understand it, the problem is that the starter turns the motor for about half a turn them the starter spins free and the motor stays still.

This is classic for a couple of teeth missing off the ring gear or wear to the ring gear and drive gear... not as unusual as you may think. The drive gear will always tend to hit the ring gear at the same spot and this causes uneven wear on the gear. AFAIK, there is no way to replace the ring gear and a replacement flywheel/clutch carrier is the only way to go.

Sorry, said it was scary

Rob

I agree mostly with Rob. He says the starter is spinning freely after first engaging. The only problem with the missing teeth, ring gear theory is that the problem does not occur when cold. I have a friend who has a similar problem on his /6. The teeth on his flywheel are warn almost halfway from front to back. All the teeth are still there. For the starter to engage properly the bendix has to extend all the way into the teeth to grab them. When it gets hot the starter doesn't always catch the teeth (perhaps due to metal expansion, or electrical resistance, or (heaven forbid) end float issues). If there is a spot on the flywheel where it is warn deeper than others then you will have the problem described even if the teeth aren't actually missing. I think if you remove the plastic cover from the rear of the starter you can look at the flywheel and check it for tooth issues.

[dougie]

I think if you remove the plastic cover from the rear of the starter you can look at the flywheel and check it for tooth issues.

Airhead dentistry. Excellent!

[George Ryals]

I think the solenoid has a pull in winding(strong force) and a hold in winding(not so strong force). If the hold in winding is faulty (when hot) the slightest bump( partial firing of a cylinder)may cause the spring to retract the bendix.