Starter spins, but that's all

Help! My '75 850 Commando has been running well, had the motor rebuilt last year and it's great. I was just in from a ride and I thought I'd try and kick start it, which I never do. Wasn't able to kick start, nothing new about that. So I just clicked the electric start, which has always worked very well. But now all I hear is the whirr of the starter, but no other sound at all, just the starter spinning. Checked the wires etc, but still, just the whirr. The solenoid looks to be the original. If I need an new solenoid, any tips on replacing it?

NoSkiddoKiddo said:

Help! My '75 850 Commando has been running well, had the motor rebuilt last year and it's great. I was just in from a ride and I thought I'd try and kick start it, which I never do. Wasn't able to kick start, nothing new about that. So I just clicked the electric start, which has always worked very well. But now all I hear is the whirr of the starter, but no other sound at all, just the starter spinning. Checked the wires etc, but still, just the whirr. The solenoid looks to be the original. If I need an new solenoid, any tips on replacing it?

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Hi, so being a ‘75, presumably it’s a MkIII? If you hear the starter spinning the solenoid is fine. It sounds as if your sprag clutch needs replacing. Look for threads on “Chinese sprag” as that seems to be the way to go.

Yes, most likely the sprag has either broken or flipped over (due to too much clearance) or the anti-backfire device has lost its adjustment. If the starter motor is spinning then it's unlikely to be the solenoid or any other part of the electrics.

https://www.nwno.org/resources/OldBrittsWebsite/e_start_gears.html

Sprag not engaging. Could be broken, cage deformed or if your lucky the teeth (or dogbones) just not engaging. The last sprag i replaced had a habit of doing this if i exceeded 90 mph. The teeth were flung out and would stick in the sprag cage, so not engaging, easily seen when stripped. That sprag lasted for a year until the the cage deformed and jammed in the 'disengaged' position. Chinese sprags can work well but they are not immune to failure either. I Had an 18 tooth Chinese sprag last three years, work faultlessly until one day, i stalled in traffic, hit the button, the engine started along with a horrible grating, whirring noise. Shit, I thought i know what that is. The sprag had broken up and jammed the starter gear. I pulled off the road and got recovered home. It took out the starter motor as the engine spun the starter to revolutions that it cannot withstand.
You might get the sprag to engage if you rough up the drive gear snout (the bit that sits inside the sprag) with course emery tape, the snout can have a too high a polished finish, so prompting slippage. If you do this plug the needle roller with something so you don't get emery dust in it. Importantly, work the emery along the axis of the snout, not round and round.
The original prestolite solenoids are crap, I've had two fail. The lucas ones for a mini are far better and fit straight in.

When my (Andover Norton supplied) sprag was practically new (I'd had to replace the one my bike came with), I gave the bike a couple of kicks, then went on to the starter button. The starter just whirred round, the sprag failed to engage. I put it on the centre stand, then in gear, rotated the back wheel by hand, just to turn the engine over. Clutch in and hit the starter again, off it went fine. I have repeated this once more, a couple of years ago. My ignorant theory: I think kicking it over can cock the sprag into the wrong position and it fails to catch. Not every time, but occasionally. 4 years on, it's still starting on the button with that same sprag.

Yep, been there and had to do that. I just engaged 2nd gear and paddled the bike backwards and listened for the starter motor to turn backwards, then into neutral and go for a start. Worked about 80% of the time.

dobba99 said:

Yep, been there and had to do that. I just engaged 2nd gear and paddled the bike backwards and listened for the starter motor to turn backwards, then into neutral and go for a start. Worked about 80% of the time.

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Yes,putting the engine at just past TDC before hitting the 'lectric leg seems wise...gives it a chance to get the crank spinning before hitting next compression point. Basically same prinicple as when using the meat and bone starter.

Also, be aware of a badly wetsumped engine, yes even mk3 can suffer this...the starter will fail, damaging sprag and/or the anti kickback device. Ive been workong on a friends mk3 ti resolve blown sprag and blown kickback device..both from running starter with 2L of oil in the sump.