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MK3 rear axle

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Re: MK3 rear axle

Postby jeffdavison » Fri Aug 04, 2017 6:50 pm

If you build them, I will come.

JD
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Re: MK3 rear axle

Postby mdt-son » Sat Aug 05, 2017 1:20 pm

madass140 wrote:well that makes it a bit clearer. Well from what I can see, the only way to fit a one piece axle is to revert to a 9/16" axle which in
one way a step backwards going to a smaller diameter and it would entail different bearings and spacers . All a bit cost prohibitive.
If I had my own MK3 I may consider a one off for myself at bugger all cost. I think we have to shelve this idea for the time being.


Don and all,
Mk3 rear axle is really poorly designed. In the interest of safety i would suggest altering the swingarm by machining (milling) the LH swingarm slot to the same shape as the RH slot, thus providing a 17mm axle dimension right through. Sure, this is a non-reversible action, but a spare swinging arm may still be purchased by those wanting to return to originality in the future ....
Going by the image in the parts book, the S/A axle supporting plates are of identical outer dimensions. Maybe someone can confirm this as my bike is in a remote workshop.

Don, if you would like to make an initial sample along these lines, I volunteer as tester.

-Knut
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Re: MK3 rear axle

Postby o0norton0o » Sat Aug 05, 2017 11:46 pm

mdt-son wrote:Don and all,
Mk3 rear axle is really poorly designed. In the interest of safety i would suggest altering the swingarm by machining (milling) the LH swingarm slot to the same shape as the RH slot, thus providing a 17mm axle dimension right through. Sure, this is a non-reversible action, but a spare swinging arm may still be purchased by those wanting to return to originality in the future ....
Going by the image in the parts book, the S/A axle supporting plates are of identical outer dimensions. Maybe someone can confirm this as my bike is in a remote workshop.

Don, if you would like to make an initial sample along these lines, I volunteer as tester.

-Knut


I did exactly what you suggested. I bought a second swingarm and had a machinist mill the slots out to use a one piece 17mm axle. In my case, I modified the swingarm slots to use a yamaha cast wheel who's axle size was 17mm.

IF the only part of the MK3 rear wheel assembly which is not 17mm is the axle slot, then it might be easy to convert an MK3 to a one piece 17mm axle. The 17mm yamaha axle I used in my modified swingarm is available on ebay for about $15. I also bought the axle spacers on ebay too.

I never had an issue with the 2 piece axle on my commando, but I always thought it was weird. Now that I have a 1 piece 17mm axle I have one less flaw to worry about.
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Re: MK3 rear axle

Postby mdt-son » Sun Aug 06, 2017 3:54 pm

o0norton0o wrote:
I did exactly what you suggested. I bought a second swingarm and had a machinist mill the slots out to use a one piece 17mm axle. In my case, I modified the swingarm slots to use a yamaha cast wheel who's axle size was 17mm.

IF the only part of the MK3 rear wheel assembly which is not 17mm is the axle slot, then it might be easy to convert an MK3 to a one piece 17mm axle. The 17mm yamaha axle I used in my modified swingarm is available on ebay for about $15. I also bought the axle spacers on ebay too.

I never had an issue with the 2 piece axle on my commando, but I always thought it was weird. Now that I have a 1 piece 17mm axle I have one less flaw to worry about.


Excellent contribution, thanks!

Going by the bearing sizes, a one piece 17 mm axle right through should work just fine. All we need now is length and thread length.

Last night I played with the idea of upping a one-piece axle to 20mm, or designing a stronger two piece axle. While other parts could accomodate a 20 mm axle by machining the parts (esp. the sprocket), this would require a drive side hub bearing bore of minimum 42mm diameter which is not possible using the factory casting, save for the lockring 06-5548. Thus, either a custom hub or a third-party cushioned hub would have to be adopted (e.g., by RAD). I guess this venture is too radical for most of us, and if the 17mm axle works strength-wise for Mk1-2 models, it will probably work for the Mk3 too (though latter has more axle loading than the previous models).

-Knut
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Re: MK3 rear axle

Postby madass140 » Sun Aug 06, 2017 4:20 pm

there is a bit more to it than just removing the old axles and sliding a 17mm axle thru the existing parts.
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Re: MK3 rear axle

Postby Mr. Rick » Sun Aug 06, 2017 4:29 pm

...and if the 17mm axle works strength-wise for Mk1-2 models...
I believe the previous models are riding on a 9/16" (14.3mm) rear axle.
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Re: MK3 rear axle

Postby o0norton0o » Sun Aug 06, 2017 6:16 pm

For all practical purposes my 17mm axle is bulletproof. Something else will break, like the cast aluminum hub, before that 17mm axle breaks, so a 20mm diameter axle doesn't increase the strength of the weaker parts that will fail first under stress so a bigger axle is pointless. Since the wheel I was adapting was already from a bike using a 1 piece axle, I only had to figure out spacers to make the wheel fit centered between the arms of the norton swingarm. The internal hub spacers were already set up to work from the donor bike with the 17mm axle.

If Don says adapting a 17mm axle to MK3 has more issues than just widening the axle slot, I would believe him, since he makes the kit to adapt the early model commando to use a 1 piece axle... so he knows.

My bike had the early bolt up hub and 9/16 diameter 2 piece axle and it never failed me, unlike some other people who weren't as lucky as I. My move to a 1 piece axle came purely because it was the simplest place to adapt the chosen yamaha wheels to the norton swingarm.

Just to make Don's point about there's often "more to it", I had other issues too... I moved the speedometer gearbox to the front wheel. I made a custom brake cable to reach the new drum brake now located on the timing side of the bike hub. I had the sprocket carrier turned down .25" to align the sprockets. I welded a brake "stand off" onto the swingarm to recieve the torque arm of the brake hub on the timing side, and I welded a stud to hold the brake cable end on the timing side of the swingarm near the swingarm slots... I could list more...

So, be aware that prototype modifications can snowball from inexpensive and simple to complicated and costly. I know this from experience. I can also say that I love my bike as it is now too, but never expected to put as much into it in time and money as I eventually did.

With that being said, IF I wanted to adapt an MK3 to have a 1 piece axle, I would probably do it and bugger all the costs... but that's just how I am. Obviously, I can't leave well enough alone.... 8)
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Re: MK3 rear axle

Postby Deets55 » Sun Aug 06, 2017 6:32 pm

Would using the same design, but replacing the axle with a higher grade of steel, similar to a Grade 8 bolt, be a practical solution?
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Re: MK3 rear axle

Postby mdt-son » Sun Aug 06, 2017 7:23 pm

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Re: MK3 rear axle

Postby mdt-son » Sun Aug 06, 2017 7:24 pm

Deets55 wrote:Would using the same design, but replacing the axle with a higher grade of steel, similar to a Grade 8 bolt, be a practical solution?


Unlikely. Fatigue strength usually worsens with higher grade steels.

-Knut
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Re: MK3 rear axle

Postby madass140 » Sun Aug 06, 2017 7:29 pm

"Wrong. Featherbeds and G15 series used a 2-piece 17mm axle. P11 series used a one-piece 5/8" (15.9mm) axle."

Learn something every day , cant speak of the G15 or P11 , but I better refund all those Featherbed guys I sold 9/16" One Piece Axles to.
Don
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Re: MK3 rear axle

Postby mdt-son » Sun Aug 06, 2017 7:40 pm

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Re: MK3 rear axle

Postby madass140 » Sun Aug 06, 2017 7:44 pm

the bearings are NOT mounted on the axle. unlike the front 17mm axle.
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Re: MK3 rear axle

Postby mdt-son » Sun Aug 06, 2017 7:50 pm

madass140 wrote:the bearings are NOT mounted on the axle. unlike the front 17mm axle.


Ouch, you are right, I stand corrected.

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Re: MK3 rear axle

Postby L.A.B. » Mon Aug 07, 2017 12:07 am

I can't be sure about this without dismantling the assembly (the photos were taken some time ago) but to make the Mk3 rear in one-piece it would seem to need a parallel spacer to replace the shoulder of the dummy axle.

Image


If flats were machined to match those on the dummy axle and the thread diameter also reduced to the original 9/16" size there would be no need to open the LH slot to 17mm.

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