Why does the 961 vibrate so much ?

Fast Eddie

Fast Eddie

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Let me start by saying that personally, I didn’t find that mine vibrated that badly, in fact it was part of the charm for me.

But nevertheless, they do vibrate, it’s something that all reviewers comment on, some quite negatively.

Why is this?

Some context to my pondering:

I had an 1800cc Harley Dyna, which means it had a rubber mounted engine with no balance shafts (like an old Commando), although it shook a bit at idle, it didn’t vibrate badly in use at all. I’ve replaced it with an 1800cc softail. This has the engine solidly mounted, but it has balance shafts (like a modern Commando). The solidly mounted balance shaft engine is much SMOOTHER than the rubber mounted one, in fact it is really very smooth (rather than just smooth for a Harley) in use.

So, balance shafts DO WORK.

Meanwhile, the 961 has a balance shaft AND a 270 crank layout, this is well known to be the smoothest configuration for a parallel twin, effectively making it a 90 degree v twin.

So, the 961 has the smoothest possible crank configuration AND it has a balance shaft.

So… why does it still vibrate so much ??
 
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answers on a postcard please. Meanwhile, some early ones had balancer shaft timing not correctly set up, I seem to recall.
 
Mines an early one (2011) and it doesn’t noticeably vibrate. Interestingly I did notice vibration when I test rode a new one earlier in the year.
 
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cliffa said:
Mines an early one (2011) and it doesn’t noticeably vibrate. Interestingly I did notice vibration when I test rode a new one earlier in the year.
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Like a Guzzi the 961 will smooth out with more miles under it’s belt.
 
baz said:
How? And why?
Looser piston ring grip on the bores?
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Good question!

Its definitely a ‘thing’ with some bikes though, same with Harleys.

Looser ring grip as the ring tension relaxes due to heat cycles is all I can think of. Maybe a similar thing with valve springs?
 
Fast Eddie said:
Good question!

Its definitely a ‘thing’ with some bikes though, same with Harleys.

Looser ring grip as the ring tension relaxes due to heat cycles is all I can think of. Maybe a similar thing with valve springs?
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I can only imagine ring grip tbh
Because with modern technology there should be nothing else to break in on an engine?
 
baz said:
I can only imagine ring grip tbh
Because with modern technology there should be nothing else to break in on an engine?
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I agree.

But… and I’m not being funny here… how much of the ‘because with modern technology’ does / does not apply to the 961 I wonder ?
 
Fast Eddie said:
I agree.

But… and I’m not being funny here… how much of the ‘because with modern technology’ does / does not apply to the 961 I wonder ?
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Well I'm guessing their crank grinder etc would be cutting edge
 
Elevated/Different compression ratios surely would all play a part from one engine to another
 
Good question on 961 - I certainly don’t know the answer.
In keeping with the apparent trend of shift to electric vehicles I’ve been considering replacing the engine on my ES2 with one of
these ..
CA16AD95-95FF-420E-99DB-8DB2AC8691F9.jpeg

range of course would be determined by the length of the extension cord but it should be considerably smoother than the original 100 mm stroker.
 
KiwiShane said:
Elevated/Different compression ratios surely would all play a part from one engine to another
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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.
 
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 kind of meant/thought for instance ...say a stock 103 H.D @9.7:1 compared to a stock Norton 961 @10.1:1
I haven't had the pleasure of riding a modern Norton so dont really know how much they rattle T.B.H :)
 
KiwiShane said:
I kind of meant/thought for instance ...say a stock 103 H.D @9.7:1 compared to a stock Norton 961 @10.1:1
I haven't had the pleasure of riding a modern Norton so dont really know how much they rattle T.B.H :)
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Oh I see what you mean. Well mines 1802cc, so kinda getting towards double the 961, which I would think was more relevant than a relatively small CR difference ?

But my main reason for mentioning HD was to compare their rubber mounted with their balanced engines. Cos to me that proves a solidly mounted engine with a balance shaft is very capable of being smooth… even if it’s a big daft twin !!
 
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Fast Eddie said:
Oh I see what you mean. Well mines 1802cc, so kinda getting towards double the 961, which I would think was more relevant than a relatively small CR difference ?

But my main reason for mentioned HD was to compare their rubber mounted with their balanced engines. Cos to me that proves a solidly mounted engine with a balance shaft is very capable of being smooth…
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Absolutely 👍
 
It may need a second balanceshaft instead of relying on just one. But a complete re-evaluation of the balanceshaft system is needed. For example : The power should not flow through the balance system , but rather be left alone to balance separately . I hope this is clear , this alone would make it smoother. But this drive and balance together system is central to this design . After all this time owning and driving this bike it never feels happy unless you are hard on the power , then its glorious with no time to worry about vibes.
 
Voodooo said:
Bore to stroke ratio
Piston compression height
Rod length
Rod angle
And who knows how accurate they are when they've balanced the rotating assembly
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I like this thinking and for a truly dedicated owner with resources made be our only solution .
 
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