Primary Chain

[Martyn Goodwin]

When I interviewed Craig McMartin after the race I (amongst other things) specifically asked about using the engine as a brake. First he confirmed that the actual brakes were in the religious arena - grab the lever then pray! Next he told me about using the engine to slow the bike - his words were along the lines of "we did not mistreat the bike in any way - to do so would have been silly, just down one gear at a time while trying to be gentle with the clutch"

 

[Bill Thomas]

I wonder if the Shock of the Starter did not help !, Years ago I ran an Industrial Primary chain, With a Split link, No problems. Maybe it was a faulty chain, It happens !!, Cheers Bill.

 

[davidd]

Definitely - No ESA of any sort. Confirmed in interview with Ken Horner.

Martyn

Then I am with Albervin. I know the singles have a bigger problem in this area, but most of those I know run two shock absorbers, one on the engine or clutch and one on the rear wheel. I think Maurice Candy is running three on his Manx. Stuart Hooper runs Belleville washers on his engine sprocket and I thought that Horners might be doing the same on theirs.

David

 

[vibrac]

two words: Bob Newby

 

[davidd]

two words: Bob Newby

I love the Newby, but if Bob offered an ESA I would buy it in a second.

I can only imagine that the Horners, who are so detailed and do such high quality work, were making a compromise with the rules. I would not be surprised if original cases were required necessitating the use of a triplex rather than the belt, which would necessitate a wider primary case. Having read Martyn's excellent articles on the endeavor, I cannot see a single item that did not receive a large amount of consideration.

David

 

[BigEd]

I love the Newby, but if Bob offered an ESA I would buy it in a second.

I would not be surprised if original cases were required necessitating the use of a triplex rather than the belt, which would necessitate a wider primary case. ........
David

Do the Australian rules allow a belt drive if it is unseen inside the original primary cases? I was at Bob Newbys a few years ago and he had a Vincent twin engine there that was being fitted with a belt primary drive. It was a double sided belt with the outside teeth driving the dynamo. The outer cover was not fitted at the time but I assumed (perhaps wrongly) that everything would fit under the cover. There would still be the problem of no shock absorber as toothed "rubber" belts do not stretch.

 

[greg brillus]

Eddy yes we can run belt drives here in Australia, and I certainly do on the racer I built. It appears that the Goodwood rules require the use of an original primary chain, but it is obvious that the shock loading through the drive line is too much for the available chain. I am sure they will sort something out...I am glad I don't have that issue with mine, Cheers......Greg.

 

[highbury731]

Do the Australian rules allow a belt drive if it is unseen inside the original primary cases? I was at Bob Newbys a few years ago and he had a Vincent twin engine there that was being fitted with a belt primary drive. It was a double sided belt with the outside teeth driving the dynamo. The outer cover was not fitted at the time but I assumed (perhaps wrongly) that everything would fit under the cover. There would still be the problem of no shock absorber as toothed "rubber" belts do not stretch.

I emailed Bob Newby a few days ago, and got this reply:
"Our dry clutch would fit in the position of the original chain sprocket that is inboard of the original clutch position. We make a system that uses a double sided toothed belt that will drive a small dynamo pulley from the back of the belt. I don't believe this will fit the std cover without modification though. Price for the system that includes a new clutch, 30mm double sided belt, engine pulley and dynamo drive pulley is :- £565 + post and vat. We only make these to order, delay 2-3 weeks. You can view the 40mm wide version on our website @ www.bobnewbyracing.co.uk"

What this means is that a Bob Newby belt primary drive kit replaces all the contents of your primary drive cover - it's an engine sprocket, clutch, belt drive and dynamo sprocket. You have to cut out the clutch seal area of your primary drive cover.

 

[Martyn Goodwin]

I love the Newby, but if Bob offered an ESA I would buy it in a second.

I can only imagine that the Horners, who are so detailed and do such high quality work, were making a compromise with the rules. I would not be surprised if original cases were required necessitating the use of a triplex rather than the belt, which would necessitate a wider primary case. Having read Martyn's excellent articles on the endeavor, I cannot see a single item that did not receive a large amount of consideration.

David

Hi David,

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

Martyn (btw thanks for the kind words)

 

[Howard]

A correctly designed/selected HTD type drive belt shouldn’t stretch, but the “rubber” teeth will have some flex and damping properties. I wouldn’t count on it as a shock absorber, but then I’ve never liked the ESA either.

There are toothed belts that will stretch, but not all toothed belts are made to suit a primary drive.

I had a discussion some years ago with a guy who’d “copied” a Newby type drive for his Triumph and told me the timing belts he’d bought from me were s**t, because they only lasted a mile before breaking. After 20 minutes explaining to him he’d used the wrong belts and pulleys and offering my design services for free, he told me I knew SFA and slammed the phone down.

H