starter shagged

well on my previous attempt at putting all my primary back together I did something very wrong and basically the freewheel sprocket didn't, it drove the backfire device in reverse and I didn't notice it soon enough. Result? a totaly destroyed starter motor
The armature is wrecked and the 4 pole plate don't look great although it might be salvageable. The coils are buggered also.
So in a nutshell there's not a lot of use there except the casing.
Hence the kickstart in the MPEG in the "clutch wobble" thread.
Previous to all this bovver I was very happy wi the oft maligned starter. I had fitted an Oddssey battery and 4 brush conversion and it always starter right away, although I always started on the leg when cold.
So how do I rebuild it?
I'm not especially looking to upgrade for the above reasons and am happy to use the original factory components, but I will use different/better kit if it's comparable in price.
Any thoughts appreciated as well as leads to the neccessary components.
Thanks
millard

Sorry to hear about your misfortune. If your armature & field coils are damaged, well...you need parts. If you have updated to the 4-brush conversion, that's about as far as you can go with the Prestolite starter. From what I understand a number of parts are interchangeable with Sportster starter parts, but the pinion gear on the armature may be different. The HD parts suppliers may have aftermarket (pattern) starter parts available since I believe the Prestolite unit is obsolete.

I understand Dyno Dave has a modern replacement starter from some other motorcycle application - I have no experience with them.

I'd certainly be interested in hearing how the reassembly of your primary went wrong since I'm preparing to swap out the countershaft sprocket on my Mk III. Any words of wisdom appreciated - thanks!

jumpjg said:

I'd certainly be interested in hearing how the reassembly of your primary went wrong since I'm preparing to swap out the countershaft sprocket on my Mk III. Any words of wisdom appreciated - thanks!

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I suspect from what Millard has said that he fitted the starter sprag the wrong way around?

If the engine is then started (with the kick start) the rotating crankshaft will engage the sprag which will turn the starter drive and starter motor as the engine revs up, the starter drive parts will then be spun up to a much higher speed than they were ever designed to be (and the anti-backfire clutch will not stop it as it is an overload clutch and doesn't actually stop backward rotation), -until something breaks! Personally I would do a starter test after refitting the starter drive parts by briefly operating the starter to check that the starter drive engages correctly, if operating the starter didn't turn the crank then that could possibly give a warning that the sprag wasn't fitted the right way.

I'm really not sure how it happened, but suspect that when retightening the clutch nut on the anti backfire device I went a wee bit OTT and locked the whole lot up. Though that doesn't explain why the starter ring was running with the engine instead of freewheeling. This was what destroyed the armature and coils. I didn't remove the sprag when I rebuilt it all as I knew it was the right way around because I could turn (freewheel) it by hand when I removed the alternator outrigger plate.

As for new parts, I'd be perfectly happy with a standard second hand motor as the old one worked perfectly until I buggered it.
Just wondering how often they come up for sale ??
cheers
milard

millard said:

I'm really not sure how it happened, but suspect that when retightening the clutch nut on the anti backfire device I went a wee bit OTT and locked the whole lot up. Though that doesn't explain why the starter ring was running with the engine instead of freewheeling. This was what destroyed the armature and coils. I didn't remove the sprag when I rebuilt it all as I knew it was the right way around because I could turn (freewheel) it by hand when I removed the alternator outrigger plate.

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Did you then remove the sprag and check it? As the sprag cages can (will eventually) break up, and may cause the sprag unit to jam up or not release. Also the thin tongues on the spring inside break so that the sprags do not retract properly? And you may end up wrecking the replacement starter if the sprag is faulty?
If the sprag unit you have has 14 sprags then it really ought to be changed for the later 18 sprag type.

The anti-backfire device should be set to slip at 50 ft-lbs, just *nipping it up* is not sufficient because if it does not slip when it should then the sprag unit will be wrecked if the engine kicks back hard when electric starting!

This is the result of somebody 'nipping up' the backfire clutch nut a little too much (actually they tightened it right down!!)
Starter Sprag:

I ran the engine on the kick start after putting it back together and the starter gear was all stationary, but if and when I scource another starter motor I will strip again to make sure that the sprag is right and it has the later type. I didn't know there were two types, cheers Les.
I tried setting the anti-backfire at 50 ft-lbs but still don't really know if I got it wrong and if this was the problem.
I thought when I do it again with a new motor I would fiddle it with the outer primary off and tighten up the nut untill it stops slipping and turns the motor.
What d'ya think?
cheers
millard

millard said:

I tried setting the anti-backfire at 50 ft-lbs but still don't really know if I got it wrong and if this was the problem.
I thought when I do it again with a new motor I would fiddle it with the outer primary off and tighten up the nut untill it stops slipping and turns the motor.
What d'ya think?

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You could try doing it that way I suppose?
Although the common mistake is to tighten it until it stops slipping at all, but of course it is supposed to slip occasionally as the motor kicks back, but unless you are able to *engineer a kickback* then I can't see how it could easily be set to slip accurately?

I set mine by holding the gear in a vice then and used a torque wrench with a socket jammed over short pieces of welding rod placed in the shaft splines to set the preload, that wasn't too difficult.

I think I must have started the engine over 100 times before it did kick back afterwards! And then the AB clutch slipping made a sound like the primary chain had broken! Of course some would then say "aha! that is loose...I must tighten it up a bit..."

I set mine by holding the gear in a vice then and used a torque wrench with a socket jammed over short pieces of welding rod placed in the shaft splines to set the preload, that wasn't too difficult.


yeah I tried that, I kept tightening turning the nut untill the torque wrench clicked at 50ft-lbs on the splines. Was that right?

millard said:

yeah I tried that, I kept tightening turning the nut untill the torque wrench clicked at 50ft-lbs on the splines. Was that right?

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Theoretically if the clutch is adusted correctly, and the torque wrench is set to 49 ft-lbs then it should click before the clutch slips. If the torque wrench is set to 51 ft-lbs the clutch should slip first before the torque wrench clicks.

But if the crankshaft motored the starter drive then the fault is most likely to be in the sprag assembly.

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