Sprockets,Nuts and Broken Washers - Is yours ok?

The short story is my late 2017 CR ground to a halt with a terrible noise from the right hand side of the engine and no neutral. Got it home and found that the final drive sprocket retaining nut had unscrewed damaging the shaft thread, and the sprocket had slid up against the alloy cover. I assumed gearbox damage so opened it up for a look. I didn't know if this was a symptom, as I had been suspicious of the clutch for a while, or the cause. I shall add a few further findings but it seemed that the flat land on the sprocket and the nut only overlap for a couple of millimetres so the washer gets badly squeezed out of shape. It looks as though the locking ears have been torn off by the nut being unscrewed with force but I can't see how. Bottom line is that the nut needs a flange and a better locking method. While I work on this I fabricated a more solid lock washer.

This bike has done 10,000 miles so most lower mileage bikes are probably ok but on CNW's excellent workshop guides it shows a damaged lock washer so are you sure yours is ok? It is really easy to inspect it.

Without the lock nut the output shaft can be pushed back into the gearbox where it can engage with the dogs of the gear on the same shaft. You then have no neutral. It can also easily bend the selector fork of that adjoining gear and possibly do more damage. For those who are interested this is the gearbox assembly with clutch and splined output shaft;




When I asked Norton about getting a replacement selector fork as a precaution I was told no - you can only buy a complete gearbox!!!!!!!

More reason for making sure this does not happen to you!

I has been getting terrible graunching noises from my clutch sometimes when moving off and the clutch had become quite grabby so considering their reputation I took a look. First observation was that a spacer washer between the clutch basket and gearbox plate had been turned without the assistance of any measuring equipment or a sharp lathe tool so an interference fit collar was made to replace it. Small detail but easy to fix. Next thing I noticed was that the outer clutch basket bearing almost totally sits on the narrow splines of the shaft rather than parallel which is starting to cause wear. Design fault and I assume they don't want to throw a bin full of incorrect shafts away. In this picture the spacer when fitted takes up most of the solid shaft. You can see how the land of the plines is being polished down.

The next item on the agenda was the clutch - should I replace the rivets/ plates/ springs? On inspection it all looked ok. The heads were properly peened over and tight even though they had two attempts at one rivet. At least they seemed to be interested in quality control the day they made mine! So I decided to leave it untouched as it has covered 10000 miles without loosening. I was keen to upgrade the clutch plates so after some Googling I found some nice looking UK made products from the well respected company EBC but no Norton fitment listed. With not much hope due to recent attempts to contact other companies I phoned EBC and got an immediate answer. I was then passed to Gary in Technical Support who searched their database with my measurements and found that the clutch plates matched the latest R6 plates and offered to send me a plate to try for size which arrived next day and fitted perfectly. Fantastic service!!!!! Based on this I ordered their performance cork-free clutch kit with +15% springs and both sets of plates. Arrived next day and went in a treat.

To wind forward the clutch action was not noticeably heavier at all and all grabbiness in the original clutch was replaced by a wonderfully smooth and progressive action. FYI the original plates were barely worn so that was not the issue. Also I chose to refill the gearbox with Bel-Ray Thumper Ester based gearbox oil as suggested in another thread. I originally tried this oil with the old clutch plates, without much improvement.

You’ve surprised me Clive, for a man who likes long pipes, that’s a surprisingly detailed approach

I gotta say, I think that not selling gearbox parts is outrageous. In fact, I’m surprised it’s legal. Is it the same for the engine? “You want new rings sir, certainly, that’ll be a new engine then” ?!

You’re very wise to approach it as you are and put those fixes in. It’s also very disappointing to see such design issues haven‘t been addressed prior. But knowing what we know now about Garners business methods, I guess it’s hardly a surprise !

Carry on ...

Small point on the oil Clive, it’s actually the Bel Ray sport transmission fluid that’s specifically designed for Sportster gearboxes, which the 961 is a copy of / based on.

But I don’t know what the difference is between it and the Thumper oil ...

I was also keen to peg the ring gear but with most engineering companies on lockdown I can't find anyone to carry out the work. I intend to spark erode a pilot hole through both then split them and spark a larger hole half way into each gear so the dowel is fully captive when the two gears are put together. It will give me a chance to inspect the clutch again when I get round to it. FYI Norton quote over £830 plus VAT for a complete clutch assembly and say no individual parts are available.....

Ref the clutch basket sitting on the splines I turned a collar up to within a thou or two and then milled 'fingers' out of it to precisely fit into the splines under the bearing to take some load off the splines.

I have worked on cars for years but never delved into the internals of a bike engine. In all with the excellent CNW guides, the workshop manual and several cups of tea in a warm garage I found it relatively easy and pleasant to work on. The gearbox assembly pulls out in one and you can sit with it on the kitchen table and examine the action - compare that with dropping the gearbox from a Jaguar on axle stands on the drive in the rain.... Everything is torqued up and Loctited to the book and so far the first few miles have been without problem.

In conclusion I wonder whether the graunch on pulling off, which I assumed to be the clutch, was the nut unscrewing and the sprocket drifting against the alloy housing before it drifted back in line? I would recommend a regular inspection of the tab washer as it can be done with basic tools or cheaply by your local bike shop. And definitely a gold star on the badge of EBC for their excellent service and products.

Doesn't the Gearbox come out of something else such as an Aprilia or a Harley.

Ebay shows this Sportster gearbox where the selector forks and other parts look similar if not the same.

Yes the box is allegedly based on a HD Sportec gearbox. But I don’t know how closely ‘based’ it is and whether or anything is actually interchangeable.

Clive said:

The next item on the agenda was the clutch - should I replace the rivets/ plates/ springs? On inspection it all looked ok. The heads were properly peened over and tight even though they had two attempts at one rivet. At least they seemed to be interested in quality control the day they made mine! So I decided to leave it untouched as it has covered 10000 miles without loosening. I was keen to upgrade the clutch plates so after some Googling I found some nice looking UK made products from the well respected company EBC but no Norton fitment listed. With not much hope due to recent attempts to contact other companies I phoned EBC and got an immediate answer. I was then passed to Gary in Technical Support who searched their database with my measurements and found that the clutch plates matched the latest R6 plates and offered to send me a plate to try for size which arrived next day and fitted perfectly. Fantastic service!!!!! Based on this I ordered their performance cork-free clutch kit with +15% springs and both sets of plates. Arrived next day and went in a treat.

To wind forward the clutch action was not noticeably heavier at all and all grabbiness in the original clutch was replaced by a wonderfully smooth and progressive action. FYI the original plates were barely worn so that was not the issue. Also I chose to refill the gearbox with Bel-Ray Thumper Ester based gearbox oil as suggested in another thread. I originally tried this oil with the old clutch plates, without much improvement.

View attachment 17674View attachment 17675View attachment 17676

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I used mid grade (blue) loctite on my countershaft nut threads and a new locking tab. The threads are reverse so self tightening ? Good work Clive ! This stuff really helps us out. Maybe more will buy a 961 now ? I hope so.

Good thread Clive very interesting.

Fast Eddie said:

Yes the box is allegedly based on a HD Sportec gearbox. But I don’t know how closely ‘based’ it is and whether or anything is actually interchangeable.

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Yes very similar but not the exact same. For example , MY HD XR1200 has no trap door like the picture shows above.

Would be nice to know which parts are interchangeable Tony, especially given Norton’s awful response to spares availability...

Kenny Dreer probably knows more, he would have picked one derivative and made any changes if any to that.

Clive said:

Without the lock nut the output shaft can be pushed back into the gearbox where it can engage with the dogs of the gear on the same shaft. You then have no neutral. It can also easily bend the selector fork of that adjoining gear and possibly do more damage. For those who are interested this is the gearbox assembly with clutch and splined output shaft;

View attachment 17669View attachment 17670


When I asked Norton about getting a replacement selector fork as a precaution I was told no - you can only buy a complete gearbox!!!!!!!

More reason for making sure this does not happen to you!

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Hello Clive , How much for the complete gearset ? It comes complete with trap door ?

Good stuff Clive, identifying yet another potential catastrophic failure. I must start a ‘daily catastrophic failure check list’ that I can go through before each ride! Have we had a bike spontaneously combust yet? It’s only a matter of time! No wonder my f@#*^#g hair is falling out!

Still love it though! 200km carving through the Sunshine Coast hinterland today. Just magic!

Awesome forum.

Long live Norton.

Hello,

Ollie from Thiel-Motorsport in Germany has made improved secure plates for the front sprocket.
thicker and harder material.

In my bike the nut was also loosely and the rear wheel has blocked when I shift into first gear.
It was a dangerous situation.

Panetone

Stephen_Spencer said:

Good stuff Clive, identifying yet another potential catastrophic failure. I must start a ‘daily catastrophic failure check list’ that I can go through before each ride! Have we had a bike spontaneously combust yet? It’s only a matter of time! No wonder my f@#*^#g hair is falling out!

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Seem familiar (I confess I was getting like this with mine)...?

Fast Eddie said:

Seem familiar (I confess I was getting like this with mine)...?

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Where did that come from, do you have the original mag? It's the only Ogri & Malcolm strip that I remember, the phrase "ton to nil mph in sparrow's fart time" just stuck in my mind. Can't remember the year, early 1970s?

comet said:

Where did that come from, do you have the original mag? It's the only Ogri & Malcolm strip that I remember, the phrase "ton to nil mph in sparrow's fart time" just stuck in my mind. Can't remember the year, early 1970s?

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seriously... you’ve not got the Ogri collection books...? And you call yourself a biker...!?!