500 twin counterweight?

  • Thread starter Thread starter Morizzi
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Morizzi

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Hi all,

My friend in the UK decided to unstick the clutch on my Alpino. In doing so he removed the counterweight and didn't realise it was there until the case came off or how it was orientated to the crankshaft. He also can't find any reference to it in the manual either.

Can someone please let me know how it is aligned for re-assembly?

Thanks

Rod
 
Rod it's easy to do. Ensure the left piston is at TDC then install the weight with the flat surface parallel to the cylinder base. The weight should be underneath this parallel line.

Tom
 
I believe that the works 500s retained the balancers, but with an uprated bearing [I've got the bearing spec written down somewhere]. There were some horror stories of the balancers letting go and exiting through the primary case on race machines and a number of racers removed them. Bear in mind that removing the balancer from a race bike is a very different proposition from a road bike.

Race bikes rarely, if ever, stay at constant revs whereas a road bike is more likely to be ridden at a steady rpm especially if you're travelling any distance by motorways or dual carriageways. If this steady throttle opening coincides with a rough spot brought on by the deletion of the balance shaft then you've created a problem for yourself.

I've deleted the balance shaft on my racer's engine and haven't noticed any increased roughness, if it was a road bike I'd weigh up the options carefully . It only takes 15 minutes to pop back in so I guess it's not that big a deal if the bike feels rough and you want to re-install it.
 
Tom Eatman said:
Rod it's easy to do. Ensure the left piston is at TDC then install the weight with the flat surface parallel to the cylinder base. The weight should be underneath this parallel line.

Tom
Click to expand...

Thanks to everyone for the replies.

Tom are you sure its LH at TDC? The only reason I query you is that my friend rang a Laverda guy he knows and he told him RH at TDC.  ??? Annoying when this happens don't you think.?

There is nothing in the manual we have about it and in fact we can't find a single reference or picture. It is shown in the Parts List and though this is not conclusive it is shown with the flat side up, round side down with the RH piston up.

I'm just trying to clarify it.

Thanks again

Rod.


 
Rod, I'm not sure whether it makes much difference. When the LH piston is at TDC the LH crank web is at 6 oclock and the RH web is at 12 oclock. Tom's phasing would make the balancer rotate in harmony with the LH crank web, if it was 180 degrees out [ie set at RH TDC.]it would rotate in harmony with the RH one.

On the Atlas /668 they have a double balancer ,each one of a similar size to 500s single balancer. These are 180 degrees apart and in harmony with each respective crank web.

The more I think about this , the less I understand it!
 
Looks like the idea of this thing is to counter the rocking couple caused by the 180 degree crank phasing.  My suspicion is also that it would need to be down with LH piston at TDC, my theory being that the crank balance factor is always less than 100% so the piston end of the rod has unbalanced inertia and this balance weight is kind of imitating a third piston in phase with the RH one.  Just shows that if you lop a pot off a well proven design you have to make compromises ...

Could just be a load of bollocks, though.
 
Just checked the manual, it's LH piston TDC and counterweight surface parallel to cylinder base.


bob said:
The more I think about this , the less I understand it!
Click to expand...

Bob,

As the balancer rotates in the opposite direction as the crank, it will counteract the "imbalance" of the LH cylinder leaving the RH rumbling around more-or-less on its' own.  180? twins are well balanced, one piston is always travelling opposite to the other, it's the rocking couple, dependant of cylinder spacing, that causes the vibes.  By countering one of the cylinders with the balancer, the rocking couple caused by the distance between cylinders is reduced.   Hope that isn't all bullshit......

Never noticed it before, but in the very back of my factory workshop manual is an appendix showing how the balancer is fitted to the 350!  The manual itself covers the early balancer-less 500.  Seems the 350 got the balancer before the 500!  The balancer itself is a typical Laverda method of mending things, tacking on a remedy without changing too much of the basic design.  The later balancer shaft design would be more efficient by counter-acting both cylinders.

piet
 
Thanks to all the responces.

Can I just clarify for my own mind's sake. I'm not located with the bike. I'm in Australia and the bike is in the UK. I have a photo copy of the manual but only for the 500. I don't have the 350 supplement.

LH piston at TDC with the flat part of the semi circular counterweight parrallel to the cylinder base and facing up and the round semi circular part of the weight facing down.

thanks

I've just seen the pic that has been posted. Great. it is now very clear.

Rod
 
NickNZ said:
  Just shows that if you lop a pot off a well proven design you have to make compromises ...
Click to expand...
:D :D :D Lop a pot off, and add a better combustion chamber design, 2 extra valves, and extra ratio in the 'box.... :D
 
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