Why does the 961 vibrate so much ?

probably mainly resonances at various points on chassis at various revs, all interplaying with original engine vibration. So difficult to compare to other Nortons. That close up of exhaust bracket is already showing start of a crack. Not surprised they sometimes break…..
 
probably mainly resonances at various points on chassis at various revs, all interplaying with original engine vibration. So difficult to compare to other Nortons. That close up of exhaust bracket is already showing start of a crack. Not surprised they sometimes break…..
I think the conventional wisdom is that with the hand built nature of the 961, that centre hanger was often not well aligned and therefore often under tension, transmitting vibration as a result. The reason they often fail and (anecdotally) vibrations reduce as a consequence - who knows!

The above also rings true of course Jan. Vibration was certainly dependent on how the bike was being ridden and where in the rev range it sat. It definitely reduced a significant amount over time/mileage though, for whatever reason.
 
But that doesn’t explain why the 961 vibrates more than the Harley below 5,500rpm does it ?

My original question behind this thread still stands.

I have a 1007cc Seeley Commando track bike. BIG engine, high CR, rigid mounted in a lightweight frame with a 360 crank and no balance shaft.

I do not believe it vibrates any worse than my 961 did !

With a 270 crank AND a balance shaft, the 961 shouldn’t vibrate any more than a 1200 Hinckley Bonnie.

I honestly don’t understand …
The 1200 Triumph twin has 2 balance shafts . I don't think the Harley V Twin engine has any rocking couple ? My bike got better and smoother the more miles I put on it . A good tune helps too of course. I don't doubt that a proper dynamic balancing of the 961 engine would work wonders ! I kinda wish you were still on board the 961 train FE .
 
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I suspect your running the 961 at higher revs that the Harley, which must make a difference.
Hello Bevel , Yes revs are usually higher say about 1000 more on the Norton . On the HD probably 3500 at ~ 70mph vs 4500 on the Norton .
 
probably mainly resonances at various points on chassis at various revs, all interplaying with original engine vibration. So difficult to compare to other Nortons. That close up of exhaust bracket is already showing start of a crack. Not surprised they sometimes break…..
Hi Jan , If you are looking at mine ? Yes , I welded a thick flat washer to the this area and that was 8K to 10K miles ago . If they are not tightened , they will not break .
 
On my TVS Norton, vibes only become noticeable at over 70mph (in 5th), and only then in the pegs, at any speed the bars are fine and the mirrors still usable. Wearing different boots helps, my Sidi adventure boots feel much better than the thinner Alpinestar SMX boots. Oddly the vibes get better at higher revs, over 6K, before coming back toward the red line. Its up to 1500 miles now, can't say it feels any smoother than it did when new.

BTW at 70mph on my 131ci 'Harley', its turning over at only 2600rpm in 6th. Compared that that the 961 feels quite frenetic lol.
 
… I kinda wish you were still on board the 961 train FE .
I’ve got 3 Nortons to keep me busy Tony, and they only make up a third of my stable!

And… TVS have not addressed the things that were ‘issues’ for me, and nor do they show any signs of wanting to.

So I won’t be boarding that train anytime soon mate.

But fear not… I’ve plenty of Norton-ness to keep me going…

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I’ve got 3 Nortons to keep me busy Tony, and they only make up a third of my stable!

And… TVS have not addressed the things that were ‘issues’ for me, and nor do they show any signs of wanting to.

So I won’t be boarding that train anytime soon mate.

But fear not… I’ve plenty of Norton-ness to keep me going…

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Very nice !
On my TVS Norton, vibes only become noticeable at over 70mph (in 5th), and only then in the pegs, at any speed the bars are fine and the mirrors still usable. Wearing different boots helps, my Sidi adventure boots feel much better than the thinner Alpinestar SMX boots. Oddly the vibes get better at higher revs, over 6K, before coming back toward the red line. Its up to 1500 miles now, can't say it feels any smoother than it did when new.

BTW at 70mph on my 131ci 'Harley', its turning over at only 2600rpm in 6th. Compared that that the 961 feels quite frenetic lol.
WOW that is BIG 131cid ! Is that the Sportster Featherbed ?
 
Looking at the picture I'd posted of the centre mount made me realise that there is a fundamental flaw in its design. The shaft of the steel spacer in the centre of the frame mount is the same length at the tube on the frame, so when the bolt is tightened all it's doing is compressing the slight protrusion of the rubber bush and pulling the exhaust hard against the tube, so eliminating any vibration insulation. I was going to reverse the rubber bush and spacer, but it's a pig to get out and I thought it may misalign the exhaust, so for now I have just put a thick washer between the steel bush and the exhaust. Unfortunately reversing the bushes on the right hand silencer hanger made the silencer hit the bottom of the shock, so I've reverted them and again placed thick washers to extend the centre spacer. The weather is crap here at the moment so won't get a chance to try it for a day or two.



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I agree with what you have done and went a bit further by slacking the both header front pipes nuts off and exhaust mounts. Tighten the centre exhaust bracket then retighten headers and then the exhaust mounts. Worth a try.
I don't think that is what he means to do , maybe I misunderstood. That is certainly NOT what I am doing on my exhaust.
 
I don't think that is what he means to do , maybe I misunderstood. That is certainly NOT what I am doing on my exhaust.
I’m fixing the centre mount but not rigidly. The spring keeps it from rattling, and will allow a bit of side to side movement, and as the mounting hole is slotted it can move fore and aft a little bit. I have the exhaust all mounted, but only the headers tightened. I plan to take the bike out for a ride, let it all settle into position, and then tighten the clamps.
 
I think some of us made an assessment of the security of the exhaust system as a whole, without the centre mount fitted - usually when it failed.

Had a good look with the mechanic servicing the bike when mine failed some 5 years ago+, deciding just to leave it off. Been all good since.
 
I think some of us made an assessment of the security of the exhaust system as a whole, without the centre mount fitted - usually when it failed.

Had a good look with the mechanic servicing the bike when mine failed some 5 years ago+, deciding just to leave it off. Been all good since.
The problem is that If I have to take my bike for inspection it will fail with either a broken or disconnected mount. ( they fail cars and bikes for oil leaks here 😩).
 
Hi Again , Are you still running a belt final drive ?
No, snapped two belts in the first year or so, therefore swapped to chain, which in turn allows for more gearing options. Both times, the belts snapped when changing into 2nd at high revs, guess they couldn't take the torque. With the softail swingarm design, both it and the primary/clutch needs to be removed to replace the belt.. a pita. With the chain, only the swingarm needs to be removed.
 
No, snapped two belts in the first year or so, therefore swapped to chain, which in turn allows for more gearing options. Both times, the belts snapped when changing into 2nd at high revs, guess they couldn't take the torque. With the softail swingarm design, both it and the primary/clutch needs to be removed to replace the belt.. a pita. With the chain, only the swingarm needs to be removed.
I have read that they have stronger belts now , but I suppose it's not worth taking the chance again. Are you running a #530 Xring chain or something bigger ?
 
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