Primary Chain

vibrac

vibrac

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Never used an engine shock absorber on the Egli racer but for peace of mind I changed the belt every year (Thinks: I haven't changed the belt on the comet for 3 years must do it for next season) , I also fitted a Newby clutch and belt on the Albion GF. After this years track time I guess 60% of the moans you read about the Albion box was down to the Albion clutch
 
davidd

davidd

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MartynG said:
It is my understanding that the Drive Belt used in the Newby setup itself has sufficient flex/shock absorption properties to act as an ESA
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I think that we discussed this in a previous thread. However, that thread caused me to wonder. Does the belt have shock absorbing qualities? I think the answer to that is no. These belts do not stretch to a significant extent. They really can't because if they are designed as timing or primary belts then any stretching would cause unwanted variations. Like Tim, I could use the belt for years and it only embarrassment ("why were you running a four year old belt!") that forces a change. Many bikes do not even have an adjustment for the primary belt tension. These belts do not like to be too tight.

So, I would agree with Howard that "stretch" is not designed into these belts, but maybe the design itself provides a minimal amount of damping by material design. I think that the fact that these belts have worked well on many racers has caused them to be viewed as possessing shock absorbing qualities that they may not possess in fact.

I also think that the function ESA may be different on a street bike and a racer. On the street bike it would come into play mostly in first gear from a stop and a little less in the other gears. On a racer I believe most builders are concerned about smoothing the explosions of very high compression pistons and reducing the constant torque pulses through the clutch, transmission and chain. Yes, the racing starts are violent, but slipping the clutch is an accepted racing technique and that has a shock absorbing effect that is not used that often on the street.

The Flash clutch is not quite up to the task, but all three of the Flashes in North America ran or run Barnett clutch plates. These plates, which I believe are still available, increase the performance dramatically. The reason the boxes are known as "grenades" is that the gears are not made of gear material like EN36, so teeth come off regularly. Because there is no sump, they are readily picked up and run through the cluster.

David

David
 
b'knighted

b'knighted

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Was it Carl Hungness who did MPH write ups on running a HD style belt final drive on a Comet? Hard to imagine feeding it through an RFM so maybe it was a primary drive. As I recall, the shock loading snapped the belt.
 
davidd

davidd

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b'knighted said:
Was it Carl Hungness who did MPH write ups on running a HD style belt final drive on a Comet? Hard to imagine feeding it through an RFM so maybe it was a primary drive. As I recall, the shock loading snapped the belt.
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Yes, it was Carl. It was the rear final drive also, although I do not remember how he threaded it through the RFM, but it would need a break in the frame to slip through. Harley has used them quite successfully, but I don't remember why Carl's snapped. My experience is that you have to run the Vincent chain on the loose side as it tends to tighten as it goes through the suspension cycle. This would kill a belt. I don't remember if Carl added a tensioner. Additionally, I know a Buell owner who had to sell his bike because his stone driveway caused several belts to snap when a small stone would land on the belt as it rotated.

Generally, the final belt drives have a tensioner that will allow for some variation in tightness as the suspension moves. Timing belts usually have tensioners also, but they are for ease of installation as much as they are for tension. The belts do not want to be run tight.

David
 
M

Mark Fisher

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davidd said:
Yes, it was Carl. It was the rear final drive also, although I do not remember how he threaded it through the RFM, but it would need a break in the frame to slip through. Harley has used them quite successfully, but I don't remember why Carl's snapped. My experience is that you have to run the Vincent chain on the loose side as it tends to tighten as it goes through the suspension cycle. This would kill a belt. I don't remember if Carl added a tensioner. Additionally, I know a Buell owner who had to sell his bike because his stone driveway caused several belts to snap when a small stone would land on the belt as it rotated.

Generally, the final belt drives have a tensioner that will allow for some variation in tightness as the suspension moves. Timing belts usually have tensioners also, but they are for ease of installation as much as they are for tension. The belts do not want to be run tight.

David
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whatever happened to Carl, haven't heard of him for ages, is he still around?
 
vibrac

vibrac

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On a Comet fitting a rear belt would not be a difficult task perhaps a twin a little more problematical. assuming the sprocket-pully was exposed and the rear wheel out I would go for slipping out the RFM spindle and pulling the RFM back the real question is the space available when you undo the 597 bolt that fixes the 45 degree rear tube to the end lug what else would have to loosen or take off would come up during the session.:D
As to primary belt I always set the belt as instructed it should be loose enough that it can be turned 90 degrees to horizontal twixt the pullys so I guess that in itself is a shock absorber
 
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