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MK3 rear axle

Classic Norton Commando Motorcycles.

Re: MK3 rear axle

Postby madass140 » Mon Aug 07, 2017 12:20 am

Exactly L.A.B. this is what I said earlier. the only possible way is to revert to a 9/16" axle, even then the "shouldered spacer" would only have a wall thickness of approx 1.35mm which would probably still be ok, It has to have the shoulder.
And the 9/16" axle would need a 17mm shoulder on the right side for the swingarm gap.
The problem I see is owners will think going down to a 9/16" axle is defeating the whole exercise. However the one piece 9/16" axles dont have any issues.
Don
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Re: MK3 rear axle

Postby L.A.B. » Mon Aug 07, 2017 12:28 am

madass140 wrote:Exactly L.A.B. this is what I said earlier. the only possible way is to revert to a 9/16" axle,


The only part that needs to be 9/16" is the threaded section. Edit: plus the flats to fit the LH slot.

madass140 wrote: even then the "shouldered spacer" would only have a wall thickness of approx 1.35mm which would probably still be ok, It has to have the shoulder.


The axle could still be 17mm, so the spacer would be the same OD and length as the 'head' of the dummy axle.

https://andover-norton.co.uk/en/shop-de ... dummy-axle


madass140 wrote:And the 9/16" axle would need a 17mm shoulder on the right side for the swingarm gap.
The problem I see is owners will think going down to a 9/16" axle is defeating the whole exercise. However the one piece 9/16" axles dont have any issues.


The axle as I see it can remain at 17mm. Reducing it to 9/16" isn't necessary so no additional spacer.
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Re: MK3 rear axle

Postby mdt-son » Mon Aug 07, 2017 1:42 am

Mr. Rick wrote:...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.


True, but those models had a bolt-up hub /drum-sprocket, which distributes loads closer to the S/A supports. Load distribution is not comparable to the cushioned hub design.

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Re: MK3 rear axle

Postby madass140 » Mon Aug 07, 2017 2:49 am

Knut, the pre MK3 hub is a "cushion" hub and uses the same 9/16" axle set up as the earlier bolt up hubs
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Re: MK3 rear axle

Postby L.A.B. » Mon Aug 07, 2017 3:03 am

madass140 wrote:some may not agree but many have had axle breakages because of a combination of things, such as , not the best design having a relatively
small diameter axle (9/16") and threading it in to the other half of the axle assembly (the stub axle) sometimes these threads will strip or
the long axle will break at the end of its thread, remember that the root diameter of the thread is only about 1/2" so it doesnt take much
ill fitment to put stress on the axle.


If I remember correctly, the Mk3 axle thread is 1/2" UNF so even less root diameter!
Image


According to Joe Seifert, 'ZFD', in a previous 'broken axle' thread, there were five alterations made to the original Mk3 rear axle drawing.

I asked in that thread (and again in another thread) if he could give us the details of those alterations so those Mk3 axles more prone to breakage could be identified, however, nothing was ever heard.
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Re: MK3 rear axle

Postby madass140 » Mon Aug 07, 2017 3:07 am

what a can of worms, If I owned a MK3 I would be fitting a 9/16" one piece axle and appropriate spacer , but for now I'll keep away from MK3 axles.
I got to much other stuff on my plate.
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Re: MK3 rear axle

Postby L.A.B. » Mon Aug 07, 2017 3:27 am

madass140 wrote:If I owned a MK3 I would be fitting a 9/16" one piece axle and appropriate spacer


But then you'd have to fit a 9/16" ID x 17mm OD spacer (or up to three spacers, as a short wider section would be required to take the place of the dummy axle head) the total distance between one axle plate and the other, as sprocket section, hub section and caliper plate are all 17mm.

Edit: Make that up to four spacers as the disc-side spacer 06-5545 could be replaced with one of 9/16"
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Re: MK3 rear axle

Postby Mr. Rick » Mon Aug 07, 2017 12:06 pm

Makes you wonder: Why was it okay to slot the RH swingarm plate to 17, but not the left? Coulda run a 17 axle (or 2-pc with dummy) all the way across...
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Re: MK3 rear axle

Postby L.A.B. » Mon Aug 07, 2017 12:20 pm

Mr. Rick wrote:Makes you wonder: Why was it okay to slot the RH swingarm plate to 17, but not the left? Coulda run a 17 axle (or 2-pc with dummy) all the way across...



The flats and narrower LH slot prevent the dummy axle rotating with the nut or the main axle.
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Re: MK3 rear axle

Postby mdt-son » Mon Aug 07, 2017 4:37 pm

L.A.B. wrote:The only part that needs to be 9/16" is the threaded section. Edit: plus the flats to fit the LH slot.
< >
The axle could still be 17mm, so the spacer would be the same OD and length as the 'head' of the dummy axle.
< >
The axle as I see it can remain at 17mm. Reducing it to 9/16" isn't necessary so no additional spacer.


I agree, and machining the flats to a one-piece axle is obviously the best solution, although there is no need for an axle torque restraint when using a one-piece axle.

It seems we need to source a supplier in the UK for this.
L.A.B., do you know of someone who could undertake making a small batch?

I would like to propose using AISI 4340 (EN10250, DIN 1.6511) in the conditions Normalized + Quenched @ 800 ´C + Tempered 2 hrs @ 540 ´C. This will yield a high cycle fatigue sustainable stress of 500 MPa / 70 ksi (R=-1) which exhibts an elongation at break Ae = 16% approx. Stainless nut and washers, as suggested by Don.
The spacer replacing the dummy bolt head may be made of AISI 4340 in the normalised condition.

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Re: MK3 rear axle

Postby L.A.B. » Tue Aug 08, 2017 12:02 am

mdt-son wrote:It seems we need to source a supplier in the UK for this.
L.A.B., do you know of someone who could undertake making a small batch?


No, sorry, I don't.
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Re: MK3 rear axle

Postby mdt-son » Tue Aug 08, 2017 4:47 am

Hi all,

I have had an email exchange with Andover Norton on the subject. Here is a section of my letter with them:

"As for the failure rate of the Mk3 rear axle, this is clearly a high cycle fatigue failure due to inherent design stress risers. Failure will depend on loading, road conditions, mileage, riding style, and possibly manufacturing and material defects. Several of the reported breaks have been on race bikes. The lean around a course will increase axle loading towards one side (mostly the left side), thus increasing bending and subsequent crack growth.

In order to dismiss the fatigue failure problem as irelevant, one really needs to examine the service record and rider´s notes, especially of those bikes which have covered substantial mileage.

At first glance the pre-Mk3 models should be even more affected due to their thinner axle - maybe they are not used as much as the Mk3 - and/or the bearing sleeve/spacer 06.2069 acts as a reinforcing member to the axle. This sleeve/spacer is absent in the Mk3 design.

Rather than perform a re-design of the Mk3 rear axle, as a least resort I suggest the workshop manual be amended by prescribing the rear axle / dummy axle to be replaced say every 150,000 miles for safety reasons. "


As noted by Andover-Norton, examining service records also requires traceability of the fitted parts. This requirement can´t be fulfilled due to the various sources of parts.

Regards,

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Re: MK3 rear axle

Postby L.A.B. » Tue Aug 08, 2017 7:29 am

mdt-son wrote:"As for the failure rate of the Mk3 rear axle, this is clearly a high cycle fatigue failure due to inherent design stress risers. Failure will depend on loading, road conditions, mileage, riding style, and possibly manufacturing and material defects. Several of the reported breaks have been on race bikes. The lean around a course will increase axle loading towards one side (mostly the left side), thus increasing bending and subsequent crack growth.

In order to dismiss the fatigue failure problem as irelevant, one really needs to examine the service record and rider´s notes, especially of those bikes which have covered substantial mileage.


"Examine the service record and the rider's notes...." indeed. Is this serious! :)

mdt-son wrote:At first glance the pre-Mk3 models should be even more affected due to their thinner axle


At first glance it should be noted that although the Mk3 axle is thicker than pre-Mk3, the threaded section where it breaks is thinner (1/2" dia.) than pre-Mk3, not only that, but the Mk3 dummy axle isn't as substantial because it passes through the sprocket bearing and speedo drive gearbox, therefore the dummy axle isn't likely to be as rigid as pre-Mk3.



mdt-son wrote: - maybe they are not used as much as the Mk3


I doubt that. :wink:


mdt-son wrote: - and/or the bearing sleeve/spacer 06.2069 acts as a reinforcing member to the axle. This sleeve/spacer is absent in the Mk3
design.


While it's true the Mk3 assembly doesn't have the 06-2069 spacer, it does have the 06-5550 spacer but the Mk3 axle doesn't break in that area.
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Re: MK3 rear axle

Postby mdt-son » Wed Aug 09, 2017 4:11 am

mdt-son wrote:At first glance the pre-Mk3 models should be even more affected due to their thinner axle


L.A.B. wrote: At first glance it should be noted that although the Mk3 axle is thicker than pre-Mk3, the threaded section where it breaks is thinner (1/2" dia.) than pre-Mk3, not only that, but the Mk3 dummy axle isn't as substantial because it passes through the sprocket bearing and speedo drive gearbox, therefore the dummy axle isn't likely to be as rigid as pre-Mk3.


As for the dimensions, both Mk3 and Mk1/2 spindles feature a 9/16 UNF thread (18 tpi) which has a basic minor diameter of 0.4943", thus no change there. Agreed, the Mk3 dummy axle is longer and therefore not as rigid as the pre-Mk3 version.

mdt-son wrote: - and/or the bearing sleeve/spacer 06.2069 acts as a reinforcing member to the axle. This sleeve/spacer is absent in the Mk3
design.


L.A.B. wrote: While it's true the Mk3 assembly doesn't have the 06-2069 spacer, it does have the 06-5550 spacer but the Mk3 axle doesn't break in that area.


That´s not my point. In the pre-Mk3 design, the sleeve/spacer 06-2069 provides additional rigidity to the spindle because it transmits a counteracting bending moment to the cantilevered spindle on account of the dual supported sleeve (proviso tight clearance between spindle and sleeve). In the Mk3 design, the 06-5550 sleeve is supported on one side only and can´t apply a counteracting bending moment. The ball bearing in vicinity of the spindle/dummy spindle joint is not able to restrain the spindle either. Therefore, the "cantilever" spindle (I am not sure it deserves to be considered a cantilever design) is quite flimsy and will deflect considerably more at the vulnerable spindle/dummy axle joint, mainly due to the poor support condition of the spindle.

One wonders who cocked up this design when they could have adopted the pre-Mk3 design quite easily?

-Knut
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Re: MK3 rear axle

Postby L.A.B. » Wed Aug 09, 2017 4:36 am

mdt-son wrote:As for the dimensions, both Mk3 and Mk1/2 spindles feature a 9/16 UNF thread (18 tpi) which has a basic minor diameter of 0.4943", thus no change there.


Only the Mk3 dummy axle thread is 9/16" UNF.

The Mk3 axle/spindle thread is 1/2" x 20 UNF (0.4387").
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