part 2 - second alton starter failure - the fix

joe czech said:
i agree, the yves design may not be a 100% solution fix to the problem, but IMO, an improvement to the original alton design. i'm thinking a washer will address my retaining nut's step flange concern. i know someone had issues with using a serrated belleville washer, but that's tha route i'm taking. either way, if i have one more failure, my crank may be toast. i have do everything and anything, and whatever it takes to get this right.
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Yves solution looks sound to me, all I’m saying is it still relies on proper torque to make the taper work… as do all Commandos.

If you’re running out of thread, a washer should indeed cure that.

It was me who urged against the serrated bevel washer as it looks to sit on soft alloy and it will chew it up horribly I think. Many on here, myself included, use a normal plain bevel washer without issue.
 
As long as the taper sees the proper torque once then until you put a puller on the engine sprocket that sprocket is not going to move, note the number of threads asking how to get it off when even the puller will not budge the sprocket, answers include heat and hydraulic pullers. Its a holding taper not a quick release taper, the morse taper on machine tools is also a holding taper.
 
baz said:
Not quite sure what you mean? The Yves type spacer does lock on the back of the sprag
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Understand that all I'm thinking is that this could be achieved more simply by machining a slot straight across the spacer rather than the more complicated machining shown in Joe's picture
 
grandpaul said:
As long as there is still a woodruff key in the tapered shaft of the crank, ALL OTHER COMPONENTS IN THAT ASSEMBLY have to be perfectly clamped in order for the key NOT to eventually fail again.
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Yep totally agree
But it's not the woodruff key on the taper that is failing
It's the alternator key on the parallel shaft
 
nortonmews said:
Understand that all I'm thinking is that this could be achieved more simply by machining a slot straight across the spacer rather than the more complicated machining shown in Joe's picture
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I like where you're coming from but as there are at least 4 different aftermarket belt drives in use plus the original chain it would be difficult to cater for each combo. I've had no issues with mine either and I firmly believe it's because I fitted a Belleville washer under the (albeit reversed ) nut as it keeps a larger area of the outer sprag plate in tension. However, I am seriously considering taking it all apart and removing the woodruff key completely. Personally I would rather the sprag slipped than the broken key wreck the pto shaft.

Another thought I had is just to cut a slot in the spacer and put a piece of square key between it and the existing machined keyway slot on the sprag. If that should happen to shear much less damage would result.

It would be also really valuable to know if any primary drives are common to the failures ( i.e. original chain, Norvil belt, Maney belt, RGM belt etc....) Maybe the belts offer less shock loading on the sprag for example.

Mine is fitted to a Norvil belt drive primary.
 
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I stated this in an earlier post I know
But it really would be nice to know how many Alton's are out there working just fine
And how many have sheered the alternator woodruff key?
 
And how many folks can honestly say they haven't tried to start the bike when it was in gear without the clutch disengaged? I am definitely guilty.


There is also an advisory from Alton at the end of the install manual..

"WE RECOMMEND OWNERS PULL THE CLUTCH LEVER IN AS A SAFETY AND PERFORMANCE FEATURE. SAFETY - SINCE THEN THERE IS NO ISSUE IF THE BIKE IS LEFT IN GEAR. PERFORMANCE - AS THE STARTER IS NOT TURNING THE GEARBOX OVER WHILST IN STARTING SEQUENCE, JUST THE CLUTCH BASKET THUS SAVING A LITTLE WEAR AND TEAR."
 
cliffa said:
And how many folks can honestly say they haven't tried to start the bike when it was in gear without the clutch disengaged? I am definitely guilty.


There is also an advisory from Alton at the end of the install manual..

"WE RECOMMEND OWNERS PULL THE CLUTCH LEVER IN AS A SAFETY AND PERFORMANCE FEATURE. SAFETY - SINCE THEN THERE IS NO ISSUE IF THE BIKE IS LEFT IN GEAR. PERFORMANCE - AS THE STARTER IS NOT TURNING THE GEARBOX OVER WHILST IN STARTING SEQUENCE, JUST THE CLUTCH BASKET THUS SAVING A LITTLE WEAR AND TEAR."
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Blimey I've never seen that before !!!!
 
baz said:
Yep totally agree
But it's not the woodruff key on the taper that is failing
It's the alternator key on the parallel shaft
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another thing to note - the woodruff key on the tapered part of the crank appears to be larger than the key used on the rotor. i'm sure norton designed the holding taper and larger key to withstand crankshaft forces whereas the rotor key is only there to position the rotor. there are no additional forces or loads applied to the original alternator rotor. adding a alton sprag clutch assembly is pushing the limits of norton's original design for the rotor key. by adding the Yves fix, retaining nut torque aside, it distributes excessive loads and forces from a singular woodruff key to the two spacer flats and two crank gear/coupling spacer pins. another note, norton's original rotor retaining nut is coupled with an internal tooth lock washer.

here's the bellville washer i'm planning on using - https://www.mcmaster.com/90895A216/ -- i'm also going to bump the retaining nut torque to 80 ft.lbs. 80 is still well within the torque limits for a 5/8-20 fastener.
 
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baz said:
Yep totally agree
But it's not the woodruff key on the taper that is failing
It's the alternator key on the parallel shaft
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Well, the same fact applies. The key doesn't hold the rotor ON, it only holds it in alignment. (but I think the point has been made more than once already, and you are aware of it, obviously).

"For the want of a washer..."
 
cliffa said:
... I am seriously considering taking it all apart and removing the woodruff key completely. Personally I would rather the sprag slipped than the broken key wreck the pto shaft...
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YIKES!

If it loosens a bit, it will still trash the shaft. Key or no key. Why offer it a BETTER chance of happening?
 
cliffa said:
And how many folks can honestly say they haven't tried to start the bike when it was in gear without the clutch disengaged? I am definitely guilty.


There is also an advisory from Alton at the end of the install manual..

"WE RECOMMEND OWNERS PULL THE CLUTCH LEVER IN AS A SAFETY AND PERFORMANCE FEATURE. SAFETY - SINCE THEN THERE IS NO ISSUE IF THE BIKE IS LEFT IN GEAR. PERFORMANCE - AS THE STARTER IS NOT TURNING THE GEARBOX OVER WHILST IN STARTING SEQUENCE, JUST THE CLUTCH BASKET THUS SAVING A LITTLE WEAR AND TEAR."
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My first car was an NSU 1000. The owner's manual said that in an emergency you could put the car in first gear and use the starter motor to get you to the side of the road. I suspect that my cNw e-start might survive that - the Alton, not so much.
 
maylar said:
My first car was an NSU 1000. The owner's manual said that in an emergency you could put the car in first gear and use the starter motor to get you to the side of the road. I suspect that my cNw e-start might survive that - the Alton, not so much.
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Did the NSU Manual state you should remove the spark plugs first?
 
grandpaul said:
Well, the same fact applies. The key doesn't hold the rotor ON, it only holds it in alignment. (but I think the point has been made more than once already, and you are aware of it, obviously).

"For the want of a washer..."
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I was answering your point about the tapered shaft key failing
This is not the issue here if it were it'd also apply to the cnw starter the qpd starter the Kickstarter and bump starting etc
Agreed the whole lot works as a package
 
Much ado about a washer...

Please see the picture - The nut is 27mm AF, the section of the drive hub that is taking the compressive force to the spacer and to the engine drive sprocket is 30 mm OD, so there is already a significant coverage of the available area between the nut and the hub OD. Adding a washer is not going to have much of an affect.

Starter Drive Cross Section.jpg


Where I do see some possible benefit is in adding a 2.25" OD washer (https://www.mcmaster.com/91525A421/) to help to add support to the area where my starter drive broke out and possible reduce flex in this area. There is a significant bending moment on the thin flange, induced by the chain pull acting asymmetrically to the assembly. The bearings / sprag clutch carry a portion of this load, but some of it will get back to the 2mm thick flange.

As can be seen, this pushes the nut out about 4 mm from it's original position, impacting thread engagement. On my bike, roughly 3mm of thread protrudes from the nut, the neck of the nut should be extended by the thickness of the washer to compensate.

Increasing the nut torque is where the largest gains come from IMHO.

My $0.02
 
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