Interesting 961 History Info

worntorn · Jan 9, 2021

Triumph saw fit to put 2 balancer shafts in the 1200 , which also has a 270 crank.
Even the Daytona 955i Triple has a balancer. You can lay your hand on the tank at idle or 12,000 rpm/ 161 bhp with negligible vibration felt.
If the balancer shafts are hurting power output in those two, engines, it's not noticed.
I think the balancer shaft is a wonderful thing. We can have an engine run at 12 or 14 thousand rpm, make insane power and without the need to build half the bike out of rubber ( 750/850 Commando) trying to get away from the vibration. I love my old Commandos, but the rubber mounting is kind of a hokey way to utilize a tremendously out of balance engine. At that we still suffer some annoying shaking below 3000 rpm. A 270 crank could help a bit, but with the higher revs used now in most modern engines to get at higher power, ugly vibrations would likely remain.
It makes sense that someone decided to fix the engine to solve the problem. I suspect balancer shafts are here to stay. If they are made correctly, they are brilliant!

Glen

Fast Eddie · Jan 9, 2021

We seem to have gone a tad off track...

How dya know it doesn’t hurt power Glen? You haven’t tried without!

I wasn’t saying balance shafts don’t work, or shouldn’t be fitted, especially to modern high rpm smooth engines !

But does a track focused 961 need one? In which, the crank and balance shaft are both out of balance as supplied by the factory!

And ref the 180, a 270 crank is inherently smoother than a 180. Phil Irving worked this out in the 1950s.

TonyA, ref the dummy shaft, it wouldn’t be needed if the noisy horrid gear primary and fragile clutch were binned and replaced with a belt drive and better ‘off the shelf’ clutch...

But alas, it would take greater skill, more motivation, and much deeper pockets than I posses to try any of this out !

BritTwit · Jan 9, 2021

worntorn said:
Even the Daytona 955i Triple has a balancer. You can lay your hand on the tank at idle or 12,000 rpm/ 161 bhp with negligible vibration felt.

Glen

I hope folks don't think that only twins gave balancer shafts.
Because several multis do as well, like the Yamaha R1, YZR, Kawasaki ZX-14, etc.......
Once twins grow larger than 500cc they produce significant vibes that must be addressed.
When 4 bangers grow above 1000cc or so their vibes become annoying too.

Fast Eddie · Jan 9, 2021

You’re right there, many big 4 cylinder motors have them these days.

But those motors aren’t as well balanced as us Nortoners might think. I read a quote from APE racing on this:

“None of these cranks are well balanced from the factory. They are, after all, street bikes that spend most of their time under 4000 RPM. If a crank is heavy where the factory can not drill holes, they are done, it goes in a motor. Yamahas are the best with Honda being worse overall. We have seen stock busas out 8 grams”.

And also from APE on the balance shaft topic:

“Any motor that is going to be raced should be race balanced. We get then to less than 1/3 gram end for end. We always recommend this if the balancer is removed. We get many reports that the cranks we have balanced and the balancer removed are smoother than stock”.

So I gotta say, I’m still thinking that a 961 with a well balanced crank and rod assembly may well turn out as smooth or smoother than stock, and certainly smooth enough for a track day hot rod!

Its all pie in the sky though. I’ll let you know how it turns out when I’m done, just don’t hold your breath waiting...!

worntorn · Jan 9, 2021

Fast Eddie said:
How dya know it doesn’t hurt power Glen? You haven’t tried without!

I don't know if there is power lost by the balancer, however my comment was, if it's hurting power on those two engines, (955i, &1200) it's not noticed. Meaning I'm having enough trouble hanging on as it is! When the Daytona hits 8,000 rpm it's all I can do to keep up with it . You have to stay forward to keep the front end reasonably close to the ground thru 1st and 2nd. Second tops out at 105 mph at which point the front wheel settles down to the pavement then lifts briefly again in 3rd
No traction control or wheelie control on that old bike means full throttle is full power.

It could be that with the balance shafts removed, there might be a couple of extra horsepower. I sure wouldn't notice it.
Some racers have tried removing the balancer with the 955i, but all I have read about eventually failed.
The engines blew up or vibrated so badly that rad mounts and other things broke.
Jim ( Bushman) found that the balance shaft in his 961 was wonky and making things worse. He corrected that as well as the crank problems and now the engine runs quite smoothly.

Glen

BritTwit · Jan 9, 2021

Fast Eddie said:
So I gotta say, I’m still thinking that a 961 with a well balanced crank and rod assembly may well turn out as smooth or smoother than stock, and certainly smooth enough for a track day hot rod!

Its all pie in the sky though. I’ll let you know how it turns out when I’m done, just don’t hold your breath waiting...!

Well, I think this whole vibes issue has been done to death on the Classic forum already.
A parallel twin with a 270 degree crank will surely have less vibes due to primary imbalance than a 360 degree twin.
But it will have additional vibes from a rocking moment, where the 360 engine will not.
An unbalanced 1000cc - 270 degree twin engine, is bound to have significant vibes, even if the crank/rods/pistons are carefully dynamically balanced.
The pistons and rods counteract the flywheel mass in the vertical plane.
The villain is the crankshaft flywheel mass moving forward and back each engine revolution that has no counteracting mass.
It would be interesting though to see what an unbalanced 961 is like.
Especially if it were to be instrumented to measure vibes.

Fast Eddie · Jan 9, 2021

Vibration is a strange topic. Different frequencies , acting differently at different revs, etc. And, of course, different rider perceptions. The only vibration that really matters on a track bike is the vibration that breaks things. If it’s below that threshold, it generally doesn’t matter. And, that is the context in which the notion was put forward.

Nevertheless, FWIW, it is most certainly not clear that a 180 crank vibrates any less than a 360, they do vibrate differently, but which is better or worse ain’t easy to say. I know this from personal experience riding otherwise very similar bikes back to back. A 270 is definitely a better start point in the quest for a low vibe twin.

No question at all that there’s no such thing as an optimally smooth unbalanced twin.... But anyone looking for optimum smoothness ain’t gonna be riding a bloody 961... at least not for long...!

worntorn · Jan 9, 2021

In fairness, how many of those vibes are due to the " All hand built in the UK! "assembly job?
From what Jim tells me, these engines are smoothies once everything is properly lined up.
With a balancer shaft that is balanced and crank mainshafts not running in an ellipse, smoothness is possible, maybe even probable.

Fast Eddie · Jan 9, 2021

worntorn said:
In fairness, how many of those vibes are due to the " All hand built in the UK! "assembly job?
From what Jim tells me, these engines are smoothies once everything is properly lined up.
With a balancer shaft that is balanced and crank mainshafts not running in an ellipse, smoothness is possible, maybe even probable.

Absolutely, as already discussed (#16), TonyA already reported this, much smoothness can be discovered this way. Still wouldn’t expect it to match your Thrux tho...

worntorn · Jan 9, 2021

One of the many Triumph engineers named Simon claimed that they felt that the new motor was too smooth initially, so they added some engine texture via fuel mapping.
It does have a strong pulse when accelerating in Sport mode, but that is quite a different thing from vibration, isn't it?

Glen

Fast Eddie · Jan 9, 2021

worntorn said:
One of the many Triumph engineers named Simon claimed that they felt that the new motor was too smooth initially, so they added some engine texture via fuel mapping.
It does have a strong pulse when accelerating in Sport mode, but that is quite a different thing from vibration, isn't it?

When I rode a Thruxton I was amazed at how smooth it was. But I didn’t like that! As I said earlier, in my opinion vibration is a multi faceted thing that’s often difficult to be precise about. The pulsing you describe is still a type of vibration to me. But a good one! High frequency buzzing through the bars is a bad one. This is the type that ‘smooth’ multi cylinder engines can produce.

Perception of the rider is key too of course. I’m one of those that need a visceral riding experience, so need some vibration or pulsing to add to the experience. The idea of a turbine smooth and quiet electric bike does NOT appeal to me at all. But some would consider it the holy grail.

To each his own. Again.

TonyA · Jan 10, 2021

Fast Eddie said:
Absolutely, as already discussed, TonyA already reported this, much smoothness can be discovered this way. Still wouldn’t expect it to match your Thrux tho...

TonyA · Jan 10, 2021

The 961 is no way as smooth as the Triumph. FE , I like the idea of a full on 961 racer eliminating the balance shaft and going with a belt or chain drive with a crankshaft rebalance ! BUT , just letting you know guys know that It won't be me . If I could see a clear path to getting the parts and the expertise it could be viable. But right now I just don't see it .

Clive · Jan 11, 2021

As already mentioned, as well as in other threads, a lot of this is subjective and unfortunately we are thinly spread with few dealers so cannot compare machines. As I seem to have to escaped a lot of common issues I would be most interested for other owners to try my bike to see if it feels any different. Maybe once this is all over we can have a nice big meet-up one warm and sunny weekend! (for our more climatologically blessed cousins outside the UK this means rain a few degrees away from horizontal and to be able to turn our heated grips to Low).

How about a few owners putting dyno run results of their bikes on the forum? Although I know someone who visited several dynos with his his car and found huge variations to big-up their tuning work but the curves should still be useful.

Interesting 961 History Info

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