Cush drive , necessary or not

[john11668]

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 !   

[L.A.B.]

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."

[Rex]

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.

[cardan]

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

[john.k]

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.

[john11668]

Have managed to retain the original cam cush drive with a rather compicated coupling around it but it seems to work and starts well . We need now to convert to 12 v in order to charge the  battery . Have bought the 12 V armature for the dynamo and also the field coil , bearings and brushes .  I am told that the existing regulator should suffice. Any  thoughts

I have attached a pic of the arrangement  .  A Mk 2 version will do away with the idler and the jockey pulley for the belt
All original parts are retained so nothing is irreversible.   All a bit non PC bit it permits the wee fella to continue enjoying his bike which is the object

[Rex]

If you mean the original electro-mechanical regulator then no it wouldn't suffice for a 12V set-up. Fit a modern solid state dynamo reg like DVR2 (not to be confused with the crap AO VReg2 unit!)

[john11668]

Supplier of parts said regulator cutout should be ok .
Would like to find someone who has done this  conversion .

[chaterlea25]

Hi,
Rex is correct, you need a 12v regulator, I have converted several dynamo's to 12v
You can also get a 6v dynamo to charge a 12v battery with a suitable regulator, it needs to spin faster than a converted one to start charging though
A 6v regulator would not charge a 12 v battery
When buying the suggested DVR2 you need to specify that its a converted dynamo

Supplier of parts said regulator cutout should be ok

That statement is complete rubbish,

John

[john.k]

One warning....fitting a 12 V generator to a magdyno can quickly ruin the magneto.....what rubbish !  say the experts!........well no,the slipping gear assy on the mag will heat up and cook the mag......disable the slipping gear.

[Rex]

I've heard reports that a 6V dynamo being pushed to 12V by a reg conversion can sometimes get so hot that the comm solder connections start to melt and the solder is then flung off.
I'd prefer to fit a "proper" 12V dynamo personally, but then if the bike has a mag for ignition is a 12V conversion that necessary? I know bulbs and batteries are easier to come by in 12V but does anyone ride old bikes that much at night?

[john11668]

The dynamo with new field coil , armature and brushes will be Identical to a 12 V model so I cant imagine any difficulty with solder melting. Unfortunately we are committed to 12 V for the starter ( could not find a 6v starter of any real power) so just want to make sure the battery keeps topped up on a daylight run. We dont make a habit of riding old bikes around in the dark although I suppose it is possible to be held up.
Not  sure what the slipping gear does, or the relevance here . Will go for the solid state regulator . Wont spoil the ship for a ha'porth o' tar. Cant imagine there will be too much overheating on our country rides out, but will watch out for it .

I guess there have been a fair few 12 conversions and it it were a common problem it would be raised more frequently. As long as there is enough charge going in to keep the starter vigorous then that will be all we need . 

[mini-me]

slipping gear would, I think, refer to the slipping clutch in the magdyno.? those fibre gears won't take a lot of stress.

Lots of other solutions to your 12v considering your engineering abilities, an alternator off a Citroen 2CV used to be favourite.

I had the same problem as you are solving here, but I solved it by buying a Piaggio Scooter

[iansoady]

Looks like an interesting project. Do you have any more technical details of the starter motor, gearing, sprag etc? You never know, my right knee may give out one of these days.....

[mini-me]

You never know, my right knee may give out one of these days

I solved it by buying a Piaggio Scooter