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Flywheel Weight


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  • 9 months later...

Just reading through this old post as we are about to embark on a little flywheel lightening on a red and white Guanaco. We have done the calc's and we are looking to shave 400grams.

We are baseing this on the burgat bible of many moons ago , but this would be for a later model. Has anybody done this on the earlier Gunaco and would 400 grams sound right. I am sure a little either way is not going to make a difference but are we in the right ball park.

Also another question for the SWM officinardos here, did the frames with the flat plate around the foot rest area ie. the first yellow ones, in fact surface pre 1980 as I have come across a very nice red and white gunaco with this, coupled to an first wave swinging arm. The owner tells me its a factory bike from the 1979, just before the start of the yellow phase. Any thoughts please.

Cheers

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Hi everyone,

Very interesting set of postings here which have kept me enthralled but here is one little snippet of information which may be of interest to you - or not, but here it is anyway.

There were several comments about finding grip and whether the flywheel weight would improve or harm this elusive essential. Well very early on in the development of the very first Spanish machines to reach these shores we found that their development engineers were well versed in finding grip on the dry, dusty surfaces typical found on the Iberian peninsular - but a little lacking in understanding of the problems of dealing with a slippery damp grass hillside.

Then one bright spark thought about the effect that the application point on the radius of the rear wheel of power transmitted by the chain had on the tendency to break grip and start the rear wheel spinning, so we gathered a group of riders on several machines and brought a selection of gearbox and rear wheel sprockets to try out the theory!

We gathered at Post Hill, the practice ground rented by the West Leeds club, and got out the spanners. We soon found that there was detectable difference in the grip available on seemingly identical machines when the gearing was achieved by using the smallest rear wheel sprocket possible that gave the correct gearing. We then realised that the combination to give the same actual engine revs to rear wheel revs chosen by the manufacturers tended to err towards using the larger gear sprocket, presumably in the interest of gaining better chain life - but the smaller we could get the rear sprocket without changing overall gearing - the better the grip.

Several have mentioned the effects of changing to electronic ignition - so here's another thought for you to mull over. For many years recognised as the master of finding grip, was Hugh Viney. I observed Hugh many times but it was a long while before I spotted just what he was doing that made all the difference.

The 'crispness' of the power delivery is directly determined by the point of ignition - Ross noted that setting his carb 'over rich' gave a slightly lumpy performance which affected grip and power delivery. That's because it takes longer for the flame front to develop in the cylinder to maximum power. The same effect as a couple of degrees of retard on the ignition - which Hugh Viney achieved by fitting a long-reach ignition lever on the left hand bar with the lever sitting in the crook of his thumb and forefinger, then he used his left hand like a throttle hand as he climbed a section - or met a slithery patch - and varied the power delivery instantly. I test rode a B40 that had been fitted with an electronic magneto in place of the separate distributor fitted on the early models. The magneto mounting had been modified so that the position of the spark relative to t.d.c. was controlled by an ignition lever - and the result was the best B40 I ever rode. I'm going to feature that in ORRe shortly.

Cheers

Deryk

Edited by laird387
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  • 2 months later...
 
 

any updates on the flywheel front gentlemen?

There are two effects of lightening the flywheel, one is that the motor will pick up quicker due to less mass, the second is that it will stall easier at very low revs if it is too light.

The former is good if you ride sections that need immediate response to sharp throttle openings. The latter means that you will have to ride the bike constantly on the clutch at low revs to overcome the possibility it will stall. With the standard flywheel the SWM will drop to a virtual standstill without using the clutch, plonk very smoothly at this speed and will pick up smoothly with no snatch. With a flywheel that it too light the bike will not run as slowly without the clutch and will jerk and snatch, meaning you have to slip the clutch to overcome the snatch and stop it from stalling. If you're used to modern bikes and don't mind clutching everywhere then it's probably not going to be an issue.

In the end, it's all subjective and personal preference

First thing you have to ask is do you really need to do it as if you're not riding sections that need the engine to pick up revs very quickly there is no point. An SWM should pick up revs quick enough to cope with any classic trial and probably any easy route in a modern club trial.

Get a spare flywheel and take half a pound off it and try it. If you want more take another quarter off it until you get something you're happy with.

First thing I'd do is ride it as it is, as you might find it's fine...

As regards the lighter flywheel making it grip less in slippery conditions, it won't affect the bikes ability to grip, what it will do is make the bike spin up and break grip easier but it will still grip, just requires more input from the rider.

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There are two effects of lightening the flywheel, one is that the motor will pick up quicker due to less mass, the second is that it will stall easier at very low revs if it is too light.

The former is good if you ride sections that need immediate response to sharp throttle openings. The latter means that you will have to ride the bike constantly on the clutch at low revs to overcome the possibility it will stall. With the standard flywheel the SWM will drop to a virtual standstill without using the clutch, plonk very smoothly at this speed and will pick up smoothly with no snatch. With a flywheel that it too light the bike will not run as slowly without the clutch and will jerk and snatch, meaning you have to slip the clutch to overcome the snatch and stop it from stalling. If you're used to modern bikes and don't mind clutching everywhere then it's probably not going to be an issue.

In the end, it's all subjective and personal preference

First thing you have to ask is do you really need to do it as if you're not riding sections that need the engine to pick up revs very quickly there is no point. An SWM should pick up revs quick enough to cope with any classic trial and probably any easy route in a modern club trial.

Get a spare flywheel and take half a pound off it and try it. If you want more take another quarter off it until you get something you're happy with.

First thing I'd do is ride it as it is, as you might find it's fine...

As regards the lighter flywheel making it grip less in slippery conditions, it won't affect the bikes ability to grip, what it will do is make the bike spin up and break grip easier but it will still grip, just requires more input from the rider.

many thanks for the tips

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  • 6 months later...
 
  • 4 weeks later...
 
  • 11 months later...

Clutch side weight is 1.6kg so pick up is improved with it off. Still seems to grip ok and im still yet to stall it in the approx 6 weeks I have owned it and#33; Love it

 

 

Think 500g is nearer to the mark !

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