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Hi Folks,

I'm casting the net a bit wider to get some more opinions about balancing the clutch and cush drive (also posted on TOL but posts there get lost quite quickly)

What have folks typically done, balance all the components? Balance them as units? As we know the supplier balanced them as a unit but this seems to have had a fairly hit and miss result.

What effect does the friction plate has that moves position every time you use the clutch? Negligible? should we balance without it? and the cush drive rubbers? balance without or are they too light to matter?

I'd be really interested in folks experience with balancing where the end result was significantly less vibration.

How did you do it?

Cheers


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Bikes: '69 T120 on average (1967 rolling frame and 1971 Bonnie engine) + '56 1/2 T110 on average (58 rolling frame - with 55 iron head engine) + 74 T150 Home model.
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One of the Melbourne BSA club members has started balancing the clutch and cush drive as a unit. The feedback from the customer was very very good.

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The primary parts to balance are the basket, pressure plate and chainwheel which are all cast parts. The cover, spring and clutch plate are all made from stamped flat metal so are going to be very consistent in dimensions. The cover could have some imbalance due to differences in the rivet dimensions but since the cover is needed to mount the basket this is accounted for.
You can balance the chainwheel and basket/pressure plate as a unit but then you need some way to always align them in the same orientation.
Although the basket and pressure plate are typically balanced together it is better to balance then separately. The basket imbalance is located away from the cover and the pressure plate is located next to the cover so the two can be balanced about the pullrod axis there still can be an imbalance between the pressure plate mass centre and the basket mass centre which causes a rocking couple. This would show up if it were put on a spin balance machine.
The chainwheel is a unit so it can be balanced as such. There is not a lot of movement between the hub and chainwheel. If this were a turbine wheel then you would go through that much trouble.

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Thanks for the feedback Dave,

I've spent a few evenings playing with the clutch and hub and my static wheel balancing rig.

I'm trying to think what else could cause this high frequency vibration felt strongly through the left footpeg at 4500 RPM. I'm sure it has been there since the bike was new, with only 10'000 km I had to repair a cracked chainguard, cracked oil tank mount and the oil tank dipstick had broken off from the cap....... I'd not say it's unrideable but it makes the ride MUCH less enjoyable. I'm guessing that the reason it has such low mileage is due to this vibration.

The clutch assembly itself (fully assembled as it came from the factory) seems very well balanced, it stops anywhere when spinning it on the rig on a 8mm rectified rod..

The chainwheel unit is a bit harder to set up on the rig but it does appear to have a heavy spot but not dramatically . The same for the two units together, they seem to favour one side but there is a wide variation.

I've carefully remeasured the runout of the clutch when everything is installed into the two covers and find the best I can get is about 6 thou (0.15mm).

Over on TOL they seems to think that 6 though will lead to major vibration and is simply not good enough.

There is a very professional crowd locally who can balance anything who I am planning to talk to.

From what I understand is that if I can get the clutch and chainwheel as a unit supported on the axial bearing faces of the chainwheel and dynamically balanced that way, the out of round problem would be a non issue as the items will be fully balanced as a unit. iI there is still some runout it's irrelevant as the units will be balanced regardless? Or am I missing something? I calculate that the 0.15mm runout would be equivalent to about 1 gram extra weight on the far end. Does not seem much to me.... What is your folks experience?

John Healy has talked often about the misalignment of the clutch hub to the clutch and chainwheel, anyone know how to check this, and if this would lead to vibration?

I was hoping to find a smoking gun with an obviously out of whack clutch but no luck so far.

Any insights greatly appreciated.

Cheers

BMF


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I can feel your pain. I have fought same type vibe on 73 T 150V. Had clutch balanced , had 3 thou runout. What helped the most? Going to a lighter clutch plate helped. To my total surprise taking the engine breather out of the air cleaner helped the most! Getting all 3 cylinders working together makes a huge difference on these engines. Just something to ponder.HTH Vic

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Hi Victor, thanks for the input, what is your vibration like now around 4.5k RPM, trying to figure out what is normal here. Mine is much worse than my 71 twin.

Apparently one can use your mobile phone as a sensor to measure the vibration, bit late now as I have taken the clutch out again but for future reference might be interesting to measure the vibration for a given RPM, could give a few clues.

Has anyone built the complete assembly of the two primary covers with the cush drive and clutch and driven the lot on the bench up to 2k RPM to see what happens?


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Has always smoothed out above 4000 rpm. My vibration was between 3500- 4000. After clutch balance, a lighter disc it's much better now. Hard to get everything working together but what a sound!

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Thanks for the input Victor.

Steven A, would you be able to put me in touch with the gentleman who does the balancing in Melbourne being in Europe it's not an option but hopefully he would give me some background.

The trident been wheeled to the back of the garage 🙄 while I ponder this and deal with the knocking coming form the primary of my Tiger

At least the old Suzuki still gets me around 😜


3D TV: A format that lost a format war without even having an opponent.
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Originally Posted by DMadigan
You can balance the chainwheel and basket/pressure plate as a unit but then you need some way to always align them in the same orientation.
I believe this was done by Borg and Beck when the clutch was made. People seem to think that the parts were marked for proper orientation. I've never seen any marks but the ones I make when I disassemble the clutch.
Could be that PO had the clutch apart and put it back together out of balance?


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Hi, I sent my clutch to LP Williams to be lightened & balanced. They removed around 13 oz from the complete assembly.
Also, don't neglect to index your clutch assy to the hub.
Mine changed from 21 thousands run out down to 5 thousands just by rotating the spline location.
There's a great video on YouTube on how to index your clutch.
My 71 Rocket 3 is now incredibly smooth, no vibration spots at all.
Good luck.

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Thanks for the input Jersey tiger, my runout id 6 though which should be OK, However I've just found something quite strange but that might mean nothing ;-)

Balancing my clutch assy has stretched out to months now due to school holidays and work etc.

Before the holidays, i spun the assembled cush drive on my wheel balancing rig a few times times. Heavy spot always clearly the same place. Amounted to 5 grams out at 80 mm needed to balance it.

Left the cush drive flat on my workbench for the two months during the holiday.

Last night I spun it again on the rig to start to plan were to remove or add weight. Stopped in exactly the same place again

So far so good

Then I took off the 6 little bolts and loosened the cover to look at possible lightening the drive by machining the cover. Lo and behold a fair amont of oil came out. (as much as when I replaced the rubbers last year so it seems to be the "normal amount of oil" that gets in there and seems to stay in there) I said Uh'oh, will this effect my balance now?

Now for the interesting part, I let all th eoil drain out for a few days and retightened up the cover and bolts back on as they were and now the heavy point is in a completely different place to before.

Obviously the oil gets in and collects in one side (maybe form wet sumping?) and then seems to stay on that side. I'm thinking that if the oil can stay captive in one side of the cush drive for two months, surely it will stay that way for a few hours that we drive and can lead to vibration?

That 5 grams at 3k rpm creates 40 newtons of force on the assembly. That equates to the weight of around 40 apples spinning around in our primaries. ( I love the fact that a newton is almost the force required to hold up and average sized apple...).

Maybe I'm completely on the wrong trail and the oil will act like Dynabeads and actualy balance the cush drive, but who knows with all the movement going on in there....

Im wondering about getting a new cover (keeping the old one original) and drilling some small holes for the oil to be flung out more easily, as it definitely gest in there anyway....

Anyway, thought it interesting.

Cheers!


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I don't remember any oil coming out of my chain wheel when I replaced the rubbers.


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Interesting David, thanks for the info. Did you open the cush drive just after removing it? Does your bike wet sump?


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Some feedback, my clutch seemed to be very well balanced as a unit from the factory. Both the clutch and the pressure plate had factory balancing drillings.

Interestingly the pressure plate on its own was out by 5 grams at 8 cm, but the drillings in the clutch almost perfectly counterbalanced this, so in the end both were out of balance by 5 grams at 8 cm but together they were very close

I drilled the pressure plate to get it as close as possible to perfect balance. I also did this to the clutch cover/basket assy and essentially ended up drilling two very similar holes exactly opposite the two factory drillings. I'd love to have seen the process at the B&B factory that ended up with this arrangement. If the pressure plate was well balanced at first I think that they would not have had to touch the clutch at all.

Bottom line, I think the clutch was fine all along.

Now for the cush drive.....

With all the oil out,and with lots of spinning, I've concluded that the cush drive it out by around to 7 to 8 grams at 55mm. I balanced the unit by adding a thin plate similar to the "lock tabs" but between two adjacent lock tabs, so the process is reversible. Those two cover screws will be further out by 1/2 mm which I think is OK

This 7 grams equates to around 4 kg of force when spinning at 3 k RPM.

Bottom line, I think all the vibration was coming from the cush drive all along.

I'm going to take the assembled outer covers with the clutch and cush drive attached to be checked on a dynamic balancing machine in the next week or two. Looking forward to the confirmation (hopefully they dont say it's all out of whack or I'll lose hope!!!!).

I should be able to test it out this year at least.....


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Originally Posted by BigBars
Interesting David, thanks for the info. Did you open the cush drive just after removing it? Does your bike wet sump?
I replaced the rubbers with the chain wheel in place. Unfortunately I did not make a note of the location of the cover when I removed it. I've noticed a bit of vibration around 4500rpm since replacing the rubbers. Nobody ever mentioned that these parts were balanced, if they were. I imagine that the clutch units were balanced by B&B before being delivered to Triumph.
Yes, it wet sumps, but I never see an excess when draining the primary.


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From what I understand the cush drive was never balanced, but the clutch was. I don't think the cush drive came from B&B , only the clutch but I don't know for sure.

I'm not 100% sure that balancing the cush drive with cones etc equates to balancing it on the bearing surfaces, but I guess it should be close as all those surfaces are machined.

That's why I am looking forward to getting some confirmation form the whole assembled unit on a dynamic balancing rig.

The dream of smooth sailing.


3D TV: A format that lost a format war without even having an opponent.
Bikes: '69 T120 on average (1967 rolling frame and 1971 Bonnie engine) + '56 1/2 T110 on average (58 rolling frame - with 55 iron head engine) + 74 T150 Home model.

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