Why does the 961 vibrate so much ?

An interesting post from a new joiner to the Facebook group…

”Hi! I'm new to this group. I recently joined because yesterday I put down a deposit on a 961 SP at Crazy Horse following a couple of test rides with the Norton events team on Thursday. I rodé 2 961's , the first had only done 400 miles and the second had done 2.7k miles. I was very pleasantly surprised at how much better the ride was on the higher mileage bike”

And went on to say…

”the first bike vibrated so much that my hands went numb and it felt like the engine internals were trying to come through the seat. The second bike with 2.7k was enjoyable to ride with pleasurable levels of vibration. I would not have purchased on the strength of the first ride. ”
 
Fast Eddie said:
If you mean production tolerances between identical engines, then I do not believe that CR differences would be sufficient to cause noticeable differences in engine vibration.
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I think it’s the primary gears there straight cut but I am sure they could get them better by better tolerances
 
I have’nt heard many other 961’s in the flesh but mine appears to be quite quiet, mechanical noise certainly not excessive for an air cooled bike - the short open pipes help of course.

I used to get a numb throttle hand regularly, depending how aggressively I was riding and where within the rev range, for the first few years of ownership. Can’t remember exactly when that settled, but I get no hint of it now.

True to say also I suppose, that clatter may not necessarily lead to excessive vibration.
 
Joe 961 said:
I think it’s the primary gears there straight cut but I am sure they could get them better by better tolerances
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Good point and thats another reason for the noise as well as the vibration that some experience..
 
The gentle whirring and mild chattering of NORMAL straight cut gears is NOT the clattering and banging that worries people I can assure you.

Folks would greet me as I pulled up saying ‘sounds like your big ends gone mate’ !

Unless the play was massively too big, and then the uneven forces created by the 270 crank and balance shaft acting on these sloppy gears, that I could imagine being part of the issue?

I honestly don’t know what causes it. But I do know the noise mine made was not ok from the perspective of a mechanically sympathetic mind.
 
Fast Eddie said:
The gentle whirring and mild chattering of NORMAL straight cut gears is NOT the clattering and banging that worries people I can assure you.

Folks would greet me as I pulled up saying ‘sounds like your big ends gone mate’ !
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Indeed!
If you own a Jap sportbike, and I've owned many, with the stock-super quiet exhaust system, you can hear the primary gear whine when revving the engine. They also use spur (straight cut) gear drive in their primaries. Nothing untoward about that sound.
The grinding, or slapping noises that some 961 engines produce are another matter entirely. They would seem to indicate that something is not quite right in the motor. I have never seen any gear driven primary with an intermediate gear other than the 961's. That is where I would focus the attention of my engineering staff. If I intending to keep producing the 961 into the future, I would re-design the crankcases, and drive the balancer shaft off of the timing side, and eliminate the intermediate primary gear all together.
 
BritTwit said:
Indeed!
If you own a Jap sportbike, and I've owned many, with the stock-super quiet exhaust system, you can hear the primary gear whine when revving the engine. They also use spur (straight cut) gear drive in their primaries. Nothing untoward about that sound.
The grinding, or slapping noises that some 961 engines produce are another matter entirely. They would seem to indicate that something is not quite right in the motor. I have never seen any gear driven primary with an intermediate gear other than the 961's. That is where I would focus the attention of my engineering staff. If I intending to keep producing the 961 into the future, I would re-design the crankcases, and drive the balancer shaft off of the timing side, and eliminate the intermediate primary gear all together.
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Yes and we were told on here somewhere that both Ollie and TVS were investigating improvements….
 
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