Another MK III broken axle (2018)

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Chaztuna and others (myself included) are updating the MK 111 workshop manual concerning helpful revisions and cleaning up a few omissions.
I believe the 80 lbs./ft. in Section A causes potential problems. This might very well be changed to 50-60 and the word Axle placed after the word Spindle (in brackets) . Many on this side of the pond do not use the word Spindle.
In Section A, they refer to it as a spindle. However, I find it interesting that in Section H1 step 4, Section H2 steps 3-5, and steps 8&9, Section H3 steps 9&10 plus Section H8, step 5, they refer to it as an axle. In fact, I see no use of the word spindle in Section H. I've updated the edited manual to show both terms. In Nortons defense, they include "GLOSSARY OF PART NAMES AND ALTERNATIVES", an English to North American technical term dictionary. It's located in the front of the manual, just after the Table of Contents.
Last month, I updated the edit to include book marks to speed getting to the correct section of the manual. These book marks are functional providing you are using Acrobat Reader to view the manual. Book marks can be seen by clicking the blue icon [2nd from the top] in the gray band in the left margin of any document that provides them. Click a second time to hide the book marks. They are not available if you are viewing the manual using Firefox or MS Edge. I don't use Chrome or Safari, so no idea about those.
In my experience, a spindle is a specialized axle, generally made of wood, used in making furniture or Industrial Revolution era machinery. The Mk III rear wheel instructions had to be written fresh, as earlier models had drum brakes. It appears that by 1975, axle was the preferred term.
Back to the subject at hand; I've previously owned 3 Commandos. I never broke a rear axle [aka spindle]. I never used a torque wrench, simply my professionally calibrated arm. I, like most others, learned at an early age [15] how tight was to tight, the hard way! :( [1/4 inch UNC valve cover bolt]
 
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Good n' tight . Do not lean into it hard with a long spanner (oops , I meant wrench ! ).
From the guy on the other side of the pond.
 
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The axle is 17mm.
The metric 6203 drive-side wheel bearing is 17x 40 x 12mm which 11/16" (17.4625mm) wouldn't fit! snipped
You are absolutely correct. I suspect it comes from my bad habit of using certain Imperial or metric 6 point, heavy wall [aka impact] sockets interchangeably. When under a car, if I need an 11/16" socket, I know that I can safely use a 6 point 17mm socket and vice versa. This eliminates my having to get up from under the vehicle. This holds true for 5/16"/8mm, 11/16"/17mm, 3/4"/19mm, 13/16"/21mm, etc etc. FYI, don't try this with 12 point sockets on hex head hardware. You'll round off the heads.
 

Richard Tool

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I have always been under the understanding ( perhaps mistakenly) that an axle is continuous through its length - i.e. between its two supports and a spindle is not . In other words a spindle may only be supported on one end or it is not continuous and therefore has a second ( or more ) component that carries through to the second support.
 
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I have always been under the understanding ( perhaps mistakenly) that an axle is continuous through its length - i.e. between its two supports and a spindle is not . In other words a spindle may only be supported on one end or it is not continuous and therefore has a second ( or more ) component that carries through to the second support.
Richard wins the prize. According to Websters, his is one of the definitions

Spindle defined
 
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I would totally agree that 80 lb ft is ballpark for a grade 5 bolt. Since I reported this particular failure I suspect it's more likely a result of under torque than over torque as the nature of the break would indicate some flexing. I don't have that picture anymore but I do have the axle as it remains on my press for when I need to impress that approximate diameter on to a piece of metal. I suspect the broken end is still unchanged unless I hammered on it. Anyway, for those who've seen classic fatigue breaks, this is a poster for it. The thread base provides the focal point or stress point for the crack to begin and it slowly fatigues with a very fine grain. The unbroken last third or so let go with a course grain with just snugging torque before a torque wrench was applied. I'm quite sure I torqued the replacement to the WSM spec with no feel of over stretch.
 
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Mike, What is the diameter of your ZZR rear axle? Does anyone else have a recommendation for proper tightening of the Mk III rear axle? I see no mention of a rear axle torque in Section A of the Mk III workshop manual. Section H2 [Refitting the Rear Wheel] Step 8 says:

8 Ensure the tensioner fits snugly to the swinging arm. Tighten the right-hand axle. T i g h t e n the lower suspension [shock absorber] bolt & nut.

Looking in Sections A & H of the 1970 & up 750 manual, I don't see any mention of a torque setting for the rear axle.

Unfortunately the ZZR manual does not specify a diameter for the wheel axles and the bike is not currently accessible for me to take out and measure. But would sayits roughly thesame as my norton . What might be more important is thegrade ofsteel used? It is a tight fit through the track ends and I wonder if fit might be n issue for those reporting broken axles .
Mine is 71 like all mk3 Fastbacks . Wonder if the tolerance was changed.. 80ft/lb seems an awfful lot of torque for the application otherwise. For the record i have only ever used long ring spanneres on British bikes for doing up the axle not even a abreaker bar or torque wrench. Remember the ZZR is a 100bhp bike and has more teeth on rear chainwheel so more leverage to pull a wheel over in the event of it being loose.

I always use a torque wrench on the ZZR primarily because of it beingnew fangled metric and my arm is onlycalibrated in Whitworth. However the last time I took it in for a tyre change I note the garage did not use a torque wrench or breaker bar either. The wheel has never come lose and is fine just as they said it would be.

I suspect that if the axle is loose in the track ends even with 80ftlbs itmight chatter and that could lead to fatigueand fracture..
My inclination would be to get a replacment nt axle plated in the vicinity of the track ends
 

ZFD

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The Mk3 rear axle breakages were legion in the old days of original Mk3 axles. The drawing was later updated and all new axles now have a radius where the originals had a sharp 90° corner where the thread starts.
In my early dealer years I used to sell Mk3 rear axles all the time. Nowadays I sell hardly any. Last sold one 2 years ago, no doubt to the proud (?) owner of an original version one.
 

L.A.B.

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The Mk3 rear axle breakages were legion in the old days of original Mk3 axles. The drawing was later updated and all new axles now have a radius where the originals had a sharp 90° corner where the thread starts.

I asked some time ago if you could give information about those apparent "five alterations to the original drawing" so owners were able to identify an axle with a higher risk of breakage, but there was no answer.


In my early dealer years I used to sell Mk3 rear axles all the time. Nowadays I sell hardly any. Last sold one 2 years ago, no doubt to the proud (?) owner of an original version one.

If we could identify which ones are more likely to break then perhaps you might sell a few.
 
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Unfortunately the ZZR manual does not specify a diameter for the wheel axles and the bike is not currently accessible for me to take out and measure. But would say it's roughly the same as my Norton . What might be more important is the grade of steel used? It is a tight fit through the track ends and I wonder if fit might be n issue for those reporting broken axles . snipped
Mike, more info please. Year/make/displacement of the ZZR. I have PDF versions of over 500 motorcycle factory shop manuals. My experience with Japanese motorcycles is that their axles are considerably more robust. I'd like to determine your bike's axle diameter.

Perhaps a member who has purchased a replacement axle could provide photos of the original and the replacement? I would like to know how the factory changed that radius.

The Mk3 rear axle breakages were legion in the old days of original Mk3 axles. The drawing was later updated and all new axles now have a radius where the originals had a sharp 90° corner where the thread starts.
In my early dealer years I used to sell Mk3 rear axles all the time. Nowadays I sell hardly any. Last sold one 2 years ago, no doubt to the proud (?) owner of an original version one.
 
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Mike, more info please. Year/make/displacement of the ZZR. I have PDF versions of over 500 motorcycle factory shop manuals. My experience with Japanese motorcycles is that their axles are considerably more robust. I'd like to determine your bike's axle diameter.

Perhaps a member who has purchased a replacement axle could provide photos of the original and the replacement? I would like to know how the factory changed that radius.
+1 , that will be fine to see and know what to doe , may be just putting the axle in a lathe and make a nice radius ...........
 
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Its a 600 D2 1992 . I struggle to see that any norton commando needs 80ft torque applied to rear wheel axle... Seems like a factory bodge to cover upsome other issue. It would not be possible in the event of say a puncture to remove the wheel with the supplied tool kit. Nowadays not much of an issue but pre mobile phones it certainly would be.
 

johnm

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The Mk3 rear axle breakages were legion in the old days of original Mk3 axles. The drawing was later updated and all new axles now have a radius where the originals had a sharp 90° corner where the thread starts.
In my early dealer years I used to sell Mk3 rear axles all the time. Nowadays I sell hardly any. Last sold one 2 years ago, no doubt to the proud (?) owner of an original version one.
Must have been machined by the same guy that did the right angle machined on the drive side of the crankshaft.

Perfect text book example of how not to do it.
 
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