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520 Rear sprocket carrier for 850 MKIll

Submitted by katherine_scott on Wednesday, 26 December, 2018 - 10:38
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Commando

Ho Ho Ho

I have been running 520 sealed roller chain on my bike for a couple of years, 

The  3/8 x 1/4 (520 ) gearbox/counter shaft sprocket is readily available in a wide range of sizes at a reasonable price.  The rear sprocket is another matter only made in the original 42 tooth size IMHO its overpriced and overweight,  less you wish to take your chances on the Indian rear sprockets that are on offer, I confess, I used a couple for my initial experiments,  the quality was poor,  the drive lugs did not match the MKIII hub (first machining job) bearing oil seal hole was too large and the speedometer  drive slots were to small!  They are very soft (not great for longevity) however they machine easily, perfect for cheap test mules, 

 [img]https://i.imgur.com/Mr3FsBll.jpg[/img]

The modified Indian sprockets lasted long enough to prove that 520 into 850  was going to work fine.  I was ready to move forward with the project,  I wanted to run sealed roller X ring chain and be able to change the final drive ratio with relative ease and at a reasonable cost .

I selected  for a suitable mass produced sprocket that is available in a range of sizes starting from forty tooth up in to the fifties for those "motocorossing Superleggera  MkIII" in the twin shock series ;0)   I decided to produce the carrier on a CNC milling station , we drew up a  3d cad model of the carrier worked tool paths and programmed the mill,  there ate three operations used in the machining each carrier takes approximately 3 hours to machine, see below a few photos of the process and the end result.

[img]https://i.imgur.com/XlwPBbnl.jpg[/img]

[img]https://i.imgur.com/YlwM3Ikl.jpg[/img]

[img]https://i.imgur.com/dQRTU9gl.jpg[/img]

[img]https://i.imgur.com/2vWg4apl.jpg[/img]

[img]https://i.imgur.com/brdKx8zl.jpg[/img]

Seasonal colours ;0)

[img]https://i.imgur.com/RfL8Ltil.jpg[/img]

[img]https://i.imgur.com/yCR4Penl.jpg[/img]

Happy Yuletide

Katherine Scott 

Submitted by ashley_cutler on Wednesday, 26 December, 2018 - 20:36

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Being MKIII you can just buy the narrow section O ring chain that fits on the original sprockets without any issues - sadly it weighs 25% more than the standard chain. 

I agree,  however  that still limits you to an expensive heavy 42 tooth rear sprocket. 

 With this carrier I can run tall gearing for log runs,  and the option of a quick rear sprocket change and an extra few links in the chain I have a back road flyer.  Not to mention the reduction in unsprung weight.  Replacement rear sprockets  for under £20. 

Best regards 

Katherine Scott

 

 

 

 

 

 

Submitted by bob_johnson on Thursday, 27 December, 2018 - 11:59

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When I was considering o ring chains some years ago 'The Chainman' asked me if I was happy to give up 4 BHP if I fitted one and anyhow how many miles per year did I do. Hard to believe that I would lose 4 BHP but as he was losing a profitable sale through his advice and taking into account all other factors, I decided to take his advice and stick to a standard, good quality 5/8 x 3/8 chain. I once did 15,000 miles in 3 months round the USA on my 850 on one chain using a Scott oiler (as I always do) and as my mileage is usually about 4,000 miles per year I'm happy to put up with changing my chain every 3 ish years and changing sprockets whenever I have to take the primary chaincase off for any particular reason.

That's good millage from a chain Bob,  however the Scott oiler and their drizzling is not for me! 

I made this carrier for flexibility, ease of change, not wishing cruse the same groove for three years.

Best regards 

Katherine Scott 

Submitted by ashley_cutler on Thursday, 27 December, 2018 - 12:44

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With the amount I have eaten this week, sprung or unsprung weight is out the window!!

Submitted by hans_taylor on Wednesday, 16 January, 2019 - 18:39

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So how much can you turn them out for Katherine ?? 

Submitted by katherine_scott on Thursday, 17 January, 2019 - 19:06

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Hi Hans

 

This project was never really a commercial venture.   I made five in total the quantity was based around material and shipping cost.  There was always the possibility of running in to problems as we proved out the programme  resulting in one or more of the billets being scrapped,  however all went to plan and five were made one each for myself and my best friend the remainder were sold to fellow Mk3 owners  who requested pricing via a pm.   I have been asked to produce some more, when there are enough names on the list I will.

Best regards

Katherine Scott

Submitted by norman_lorton on Friday, 18 January, 2019 - 09:16

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Nice design Katherine and good use of quality, changeable sprockets. I would fit one just for the beauty of the design.

Like Bob I still use old style chains but with a pair in use at any time - dirty one off pulls the clean one on. After double washing I used to use a hot bath of Linklife but now it is the Morris sticky spray. A pair of chains last me 20,000 miles and I am half way through my third set (Regina).

I can appreciate that o-ring chains might have a shade more drag, but 4 BHP? One mechanical horsepower is 0.74kW, so the chain is absorbing an extra 3kW. That's going to get pretty hot if it's true.

 



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