Another clutch basket failure.

Well, Richard-7 warned us all about the possibility of failure in the rivets holding the clutch basket to the drive gear, and I've just had it happen to me. The loud noises in the primary of my 2014 961 Sport seemed like they were getting louder, so I finally pulled the primary to take a look. All four rivets had pulled out. It still worked because the rivets were still in the slots in the gear, but everything was flopping around like crazy. I'm amazed it was still rideable. I have to hunt up some special Torx wrenches to get it further apart, and then I'll post some pictures. I have several sets of Torx keys, but none or the tamper-proof style with the hole in the center that are required to remove the toothed wheel on the crankshaft. I'm hoping that I can make repairs without having to deal with trying to get parts from the new Norton.

I'm really glad I bought the tools from CNW that Richard and his dad developed. Using them is way better than trying to do it the way the service manual from Norton describes. Thank goodness for the illustrated instructions that Richard sent out.

I'm already looking forward to riding a 961 that doesn't sound like a thrashing machine.

Ken

Sorry to read this Ken. How many miles on the clock?

Ken
This happened to my 2014 -961 as well with about 2000kms on it ,
It went to the dealership under warrantee to have a new clutch basket installed,
Not sure if it was same or updated clutch basket .
But with another 17000 kms it hasn't given any trouble
cheers
Paul

I have an issue at the moment at 10000 miles which I suspect is clutch but haven't opened it up yet to confirm. Either way, hopefully as a long term owner, and engineer I am wondering how this clutch reliability problem can be eliminated. It would be great if the new company took a look at the experiences of current owners and saved themselves future grief - even if 961 production has a limited life.

iwilson said:

Sorry to read this Ken. How many miles on the clock?

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5,540 miles so far. Based on how long I've been hearing the noises from the primary area, I think it was probably already starting to come loose when I bought it with less than 400 miles on the clock.

Ken

I've seen some references here to Norton having made improvements on the clutch design during the 961 production life, but no details. Does anyone know the nature of the improvements, and when they were put in place?

Ken

If memory serves me Richard7 posted a little while back that the factory "fix" was to set the shouldered bolts in epoxy to take out any slack. Possibly effective but a bodge rather than an engineered solution if so.

Wasn't the epoxied bolt fix for the starter ring gear mounted on the clutch basket?
The ring gear was a problem on early models too.

OK, finally got the tools and got it apart. It appears that the rivets just came apart. I call them rivets, but it's kind of a weird design.

This is a picture of the basic parts. You can see two of the rivets to the right, along with the collars that appear to have been installed and then the rivets peened over in the plate to the right to keep them in place. But there's no sign in that plate of any marks from the pins being peened over, so I'm a little unsure of what happened here. I left the other two rivets the alloy clutch basket at the top to show where they fit. The rivets don't seem to have been any sort of interference fit in any of the pieces, so I'm just assuming from the looks of them that they were peened over poorly at the start. Or else that's just a really bad design.



And this is a picture of the same bits from the other side.



and this is a picture of the bits partially assembled to show how they fit together. There's also one of the rivets showing how the collar fits over it. The springs will fit in the obvious cutouts for them and the spring plate will go over them, and then the rivets get peened. At least that's how I think it went.

Edit - As Klaus pointed out to me, the gear is sitting on the clutch basket wrong side up. But I'm leaving it here because it still shows the arrangement of the bits.



I'm not sure where I'm going from here. My thought is that I could just assemble it and tig weld the ends of the pins to the spring plate. I think that would work OK, but would be a little sticky if I ever need to disassemble it to replace the springs.

I've heard that there were updates in the clutch design, so maybe the later ones were improved. If so, I could try to buy a new one through Norton's new parts system. But I'm not interested in that unless it is an improved design. Does anyone here know the story on the clutch changes?

Any other ideas?

The ring gear is nice and solid, but I still plan to put a couple of dowel pins in it.

It doesn't look like there is any other damage in the primary case. This is a photo of it with the parts removed.



Ken

lcrken said:

OK, finally got the tools and got it apart. It appears that the rivets just came apart. I call them rivets, but it's kind of a weird design.

This is a picture of the basic parts. You can see two of the rivets to the right, along with the collars that appear to have been installed and then the rivets peened over in the plate to the right to keep them in place. But there's no sign in that plate of any marks from the pins being peened over, so I'm a little unsure of what happened here. I left the other two rivets the alloy clutch basket at the top to show where they fit. The rivets don't seem to have been any sort of interference fit in any of the pieces, so I'm just assuming from the looks of them that they were peened over poorly at the start. Or else that's just a really bad design.

View attachment 16866

And this is a picture of the same bits from the other side.

View attachment 16867

and this is a picture of the bits partially assembled to show how they fit together. There's also one of the rivets showing how the collar fits over it. The springs will fit in the obvious cutouts for them and the spring plate will go over them, and then the rivets get peened. At least that's how I think it went.

View attachment 16868

I'm not sure where I'm going from here. My thought is that I could just assemble it and tig weld the ends of the pins to the spring plate. I think that would work OK, but would be a little sticky if I ever need to disassemble it to replace the springs.

I've heard that there were updates in the clutch design, so maybe the later ones were improved. If so, I could try to buy a new one through Norton's new parts system. But I'm not interested in that unless it is an improved design. Does anyone here know the story on the clutch changes?

Any other ideas?

The ring gear is nice and solid, but I still plan to put a couple of dowel pins in it.

It doesn't look like there is any other damage in the primary case. This is a photo of it with the parts removed.

View attachment 16869

Ken

Click to expand...

As you say Ken, it's a bit weird. Presumably the collars are supposed to rotate on the "rivets" ?

Yet another cost cutting piece of crap most bikes with even half the bhp that this bike makes have 6 or more rivets to transmit the engine power, a clear case of spoiling the ship for half pence worth of tar, whoever designed this clutch should have known better

I had the same failure on my clutch basket 2015 SE. I think the idea is the sapcers should be clamped between the spring plate and the clutch basket. The spacers gives clearance for the primary drive gear to move to allow the spring to act as a shock absorber. The problem in my mind with the design is how do you quality control a rivet, is it tight enough to prevent movement as any movement will reult in the assembly getting progresively looser. I got a new clutch basket which looked the saame but so far has been ok. My plan when I get round to it is to try to fit some high tensile bolts instead of the rivets to the old clutch basket. There looks to be plenty of room behind the clutch basket for a nyloc and I will probably loctite as well.

Thanks for sharing this it is the first time I've seen the clutch in its terrible naked glory. As you say replacements for the rivets could be tig welded in place with a piece of temporary shim material which is removed after assembly. I still wonder if the basket inner could be retained with the original plates and a new backing/ outer basket fitted? Perhaps something from a company like Rekluse (they look really nice) or a Triumph unit? There must be someone who custom builds race bikes who could do this?

Hello Ken , This is very good that you caught this before any damage !

spannerhands said:

I had the same failure on my clutch basket 2015 SE. I think the idea is the sapcers should be clamped between the spring plate and the clutch basket. The spacers gives clearance for the primary drive gear to move to allow the spring to act as a shock absorber. The problem in my mind with the design is how do you quality control a rivet, is it tight enough to prevent movement as any movement will reult in the assembly getting progresively looser. I got a new clutch basket which looked the saame but so far has been ok. My plan when I get round to it is to try to fit some high tensile bolts instead of the rivets to the old clutch basket. There looks to be plenty of room behind the clutch basket for a nyloc and I will probably loctite as well.

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I think a barrel style sleeve nut & cap screw would be more suitable in this application

Thanks for the replies so far. I think spannerhands is right about capturing the collars/spacers between the spring plate and the clutch basket. I'm planning to see if I can convert it to a bolted assembly, as acadian suggested. Should get to that today. It does seem to be all about the quality of the rivet. From what I can see of what's left on the ends of my rivets, it doesn't look like there was much material in the end that was peened over. Might have just needed a bit longer rivet. Or maybe it just wasn't assembled very carefully. At least it looks like I can probably fix it, one way or another.

I was considering trying to get a new one, but from what acadian said, it doesn't look like the replacements are an improvement.

The adventure continues

Ken

The other thing I noticed is that my clutch basket does not look like the ones pictured in the factory service manuals (both the early version and the Euro 4 version) and in the Cootes' service tutorials. Mine has a one piece cast basket, but the pictured ones look machined from billet, and have a steel retaining band around them. From what Nikolai said in another post, the first UK built units were machined from billet, so I assume that means I have one of the Taiwan products. Does anyone know if the UK billet clutches used the same rivet desigh?

Ken

lcrken said:

The other thing I noticed is that my clutch basket does not look like the ones pictured in the factory service manuals (both the early version and the Euro 4 version) and in the Cootes' service tutorials. Mine has a one piece cast basket, but the pictured ones look machined from billet, and have a steel retaining band around them. From what Nikolai said in another post, the first UK built units were machined from billet, so I assume that means I have one of the Taiwan products. Does anyone know if the UK billet clutches used the same rivet desigh?

Ken

Click to expand...

Oddly enough I brought up the topic of clutch baskets and revisions when at the factory today and the feedback was that the early baskets were billet and replaced by cast ones, but I didn't ask when this happened.

David Coote's 2013 basket is billet . My late 2014 is cast . So 2014 , yours looks cast like mine and part of that MK2 process . I think a lot of the clutch issues boil down to quality of assembly . At 6,500 miles my clutch basket was good and tight . I have not looked in 9,000 miles. I have a new Norton clutch basket on order , I am still waiting to hear back from Norton . If I can get a new one , I will post the condition of my current one.

McMaster Carr stocks these in 316 but not in Grade 8