Heavy Vibration Issue

Depends on your definition of ‘problem’.

Of course, the standard set up is fine, and well proven, and works perfectly for most folks.

That doesn’t make it unimprovable !

E.G:

The removal of oil gives a better clutch, with more clutch plate options.

Some of those clutch plate options are MUCH lighter than stock.

A belt is (a lot) lighter than a chain.

Alloy pulley and clutch basket are (much) lighter than steel.

A belt doesn’t need adjusting so allows for fixed gearbox mounting.

For some, that’s a lot of ‘problems’ addressed very easily and cheaply.
 
I have installed belts on three of the primaries here.
Since doing those installs, I've not had a primary leak, not even one drop of oil, from any of them. That could be because they are dry!
My bikes with primary chains and oil filled primary do have the occasional drip or three. The MK3 is the best, but even that bike develops a bit of grime on the underside of the cases after a long run. It's a minor annoyance on that bike.
Small thing I guess, like other folk here I mainly went to the belt drive on the 920 Commando for the weight savings.
On the 650ss with its leaky tin primary and slipping stock clutch, the weight savings was a bonus, the main reasons were to solve the fairly severe leakage and the slippage problems.
On the 1360 Vincent the Newby belt drive and dry clutch was a natural choice to handle the power output and to keep the weight very low.
So there were different reasons for installing belt drives on those three bikes, but all three worked out much as planned.
The oil filled primary on some bikes is just fine too. Just keep a rag handy and enjoy checking, topping up or changing the oil now and then!
Kind of like points vs EI. Both work fine but I never do anything with the EI ignitions, year after year. They just work perfectly all the time.
The points need some maintenance now and then, not a lot but it will bite you if you ignore them.
So will an oil type primary that has accidentally become dry of oil due to neglect.



Glen
 
Fast Eddie said:
You’re quite the collector Ken !

Very interesting picture, personally I don’t quite see how those strengthening mods actually strengthen the weak point ?

My hypothesis is that the cradles only break when another factor is added, ie loose engine to cradle fasteners.
Click to expand...

I think it is quite likely that loose engine cradle fasteners contribute to this type of cradle breakage, but I don't recall personally noticing loose fasteners in the one that broke on my race bike.

But your comment did remind me of another cause of vibration. As KiwiShane mentioned above, loose cradle fasteners will do that. That's not the problem here, because Dellis has already checked that. But I do have an interesting story related to loose fasteners and vibration, so I'll go ahead and include it. Back in 1984 when I first raced at Daytona, I had a problem with vibration on my 920 engined Commando Production Racer. The vibration started at higher rpms, but as I did more laps it started to come in at lower revs, and get worse. I already knew from experience that a cracked crankshaft will act like that, and only gets worse if you keep racing, until it finally breaks, so I brought the bike in and switched to my backup bike, a wideline featherbed with a 750 Commando engine, and had a fun race in a different class. To my surprise, when I later started to pull the engine from the PR, I found the cradle mounting bolts quite loose. I tightened them and tested the bike, and the vibration had disappeared.

Damn, that was 41 years ago, when I was a mere youth of 40. How quickly time goes by.

Ken
 
kommando said:
As you suggest just welding a gusset where something has broken can just move the weak point to the edge of the gusset for a new cracking point. But in this case the extra metal is full height and supporting not just the top thin section but also the middle and bottom slightly stronger bolting points. By shortening the sections subject to bending it will probably be changing the resonance frequency out of a critical range as well.
Click to expand...
Why are you bringing resonance into the discussion? Breakages are most likely caused by fatigue due to a combination of biaxial shear loads, biaxial bending loads, and twisting (torsion) causing additional shear loads.
All dynamic movements are force excitated by continously varying frequencies, even the acceleration load acting at the engine's CoG. I see small chance of ampltudes building up if all joints are tight. Besides, there is a lot of dampening in the system, by the rubber mounts and the bolted connections.

Breakages at the cradle are a result of many quasistatic complex stress conditions, in my opinion.

- Knut
 
Last edited:
worntorn said:
The oil filled primary on some bikes is just fine too. Just keep a rag handy and enjoy checking, topping up or changing the oil now and then!
Kind of like points vs EI. Both work fine but I never do anything with the EI ignitions, year after year. They just work perfectly all the time.
Click to expand...
Well, until the electronic box fries, which it will, at some point in the future. Working perfectly all the time is not a worthy superlative of belt drives!

- Knut
 
Last edited:
mdt-son said:
Well, cheaply ... keeping the chain drive is undoubtly cheaper! And don't forget to count the negative points also.

- Knut
Click to expand...
When you look at what it costs to build ‘special’ bikes / engines / etc and the cost vs benefit of some other items… a belt drive kit is very cheap IF you value the benefits.

Add to that that, those that have worn components in their chain drive system and it starts to become even cheaper, and would even be a cost saving if building something from scratch vs cost of new engine sprocket, clutch basket and chain.
 
Last edited:
mdt-son said:
Well, until the electronic box fries, which it will, at some point in the future. Working perfectly all the time is not a worthy superlative of belt drives!

- Knut
Click to expand...
You’re quite right, belts do not work perfectly all the time. I had one fail in around 1996.
 
Last edited:
Onder said:
Why?
Click to expand...
Basically… because it was an old pre unit Triton with ancient Unity Equipe engine plates that had been through a long list of young, skint, ignorant, owners, like me!

The gearbox adjuster stud / nut face was a quite chewed up (it had clearly previously been using those original Triumph washers that dig in to the plates, and weren’t really designed for soft alloy). So it didn’t really have proper faces to allow for a proper clamping. Quite possibly I didn’t tighten it properly either, and basically the chain pulled the belt as tight as a bow string until it gave up.

Honestly… not the belts fault.

Note: my arguments are IN NO WAY anti chain… I am simply trying to provide balance to the anti belt…
 
Last edited:
Fast Eddie said:
Basically… because it was an old pre unit Triton with ancient Unity Equipe engine plates that had been through a long list of young, skint, ignorant, owners, like me!

The gearbox adjuster stud / nut face was a quite chewed up (it had clearly previously been using those original Triumph washers that dig in to the plates, and weren’t really designed for soft alloy). So it didn’t really have proper faces to allow for a proper clamping. Quite possibly I didn’t tighten it properly either, and basically the chain pulled the belt as tight as a bow string until it gave up.

Honestly… not the belts fault.

Note: my arguments are IN NO WAY anti chain… I am simply trying to provide balance to the anti belt…
Click to expand...
Belts and chains are both good if setup properly
I've not managed to snap a belt as yet
But I've snapped one primary and many drive chains usually my fault!
 
And as for belts and leaks: one thing that will be noticed, that was not formerly, is any leak from the gearbox to the primary. The older, both in design and age the gearbox is, the more likely the issue. Usually it gets by the sleeve gear
bush and is then centrifugally scattered by the clutch. Ignored long enough or indeed for not long at all, you will then
be threatening belt life. Yes, I know, some run wet belt setups but doubt that is a good long term plan.
 
No leaks.
At all.
Now the collective gasp from the urists.🤣
Heavy Vibration Issue
Heavy Vibration Issue
Heavy Vibration Issue
Heavy Vibration Issue
 
Onder said:
And as for belts and leaks: one thing that will be noticed, that was not formerly, is any leak from the gearbox to the primary. The older, both in design and age the gearbox is, the more likely the issue. Usually it gets by the sleeve gear
bush and is then centrifugally scattered by the clutch. Ignored long enough or indeed for not long at all, you will then
be threatening belt life. Yes, I know, some run wet belt setups but doubt that is a good long term plan.
Click to expand...
I run a dry belt drive with an Alton starter on my commando
I made my own clutch centre nut pushrod seal and the chaincase remains bone dry
But I squirt a bit of oil into the sprag area every now and then
Even though Paul at Alton says lubricant isn't necessary for the sprag
 

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