Author Topic: Cush drive , necessary or not  (Read 279 times)

Offline john11668

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Cush drive , necessary or not
« on: May 02, 2018, 10:07:49 PM »
Hi folks
I understand that on the later B31 when an alternator was fitted , the cush drive was dispensed with!
Can this be done generally.  Would it be a problem if there was no cush drive??

The main reason for the question is that we are looking to put an electric start on a tin chaincase bike . We are looking at an  external pulley wheel with sealed sprag and we intend to try and fit a large (say 80T ) timing pulley.  This will be a much simpler task if we don't have to contend with maintaining the cush drive function.

Would be happy to here from anyone who has tried this or knows any cause, or just impediment why this may not be done.
In the search function I saw electric start  described as "wimpy".   Not for a 70 year old who is 8 stone wet through it isnt !   ;)

Offline L.A.B.

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Re: Cush drive , necessary or not
« Reply #1 on: May 02, 2018, 11:24:04 PM »

I understand that on the later B31 when an alternator was fitted , the cush drive was dispensed with!
Can this be done generally.  Would it be a problem if there was no cush drive??


As I understand it, it was the crankshaft-mounted ramp-cam shock absorber that was dispensed with in order to fit the alternator and a cush-drive clutch assembly was then used.


https://www.draganfly.co.uk/index.php/a65anda50/category/909-4-spring-triumph-type-with-cush-drive

"'4 Spring Triumph' type with cush drive - used on alternator equipped 'B' and 'M' models from 1959."
L.A.B.

Offline Rex

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Re: Cush drive , necessary or not
« Reply #2 on: May 03, 2018, 02:30:29 PM »
Yes, I would agree with that. I would think a big single bike with no cush-druve arrangements would be so horrible as to be unrideable.

Offline cardan

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Re: Cush drive , necessary or not
« Reply #3 on: May 04, 2018, 01:30:50 AM »
I would think a big single bike with no cush-druve arrangements would be so horrible as to be unrideable.

A lesson well learned from the earliest days! Here's the cush arrangement in my 1903 Columbia. It lives on a counter shaft in the normal clutch position. The previous year, the "cush" was achieved by mounting the engine drive sprocket clamped between two large washers, but otherwise unconnected to the mainshaft of the motor. It things got snatchy, the sprocket just slipped. Crude, and not very effective, but Indian used a similar arrangement on their back sprocket for a number of years.

"Something's gotta give!"

Leon

Offline john.k

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Re: Cush drive , necessary or not
« Reply #4 on: May 05, 2018, 09:24:20 AM »
Harley twins had no cush drive until the  early 60s......although an accessory was available from about 1924 onwards......as regards the BSA,the 'orrible clutch is generally replaced with a Triumph four spring,IF you can find one.