Cush Drive Crankshaft Pulley

SteveA · Dec 21, 2011

Does anyone use a Cush Drive in their engine pulley with a belt drive.

I am looking to source one for a 40mm belt (8 or 10mm teeth?, I don't have a Clutch drum yet, but it will be 70 tooth). What I do know is that I want to run a high ratio primary so want 40 teeth on the pulley, which should give abit more room for the cush mechanism.

The application is a Rickman Norton, and I don't want to run a Cush Drive rear wheel as they did not have these and I want to run an original style swinging arm and hub.

Any ideas or experience appreciated.

Steve

Fullauto · Dec 21, 2011

Don't think you'll need it with a belt drive. Let's face it, the hard lumps of whatever it is they use in standard Norton hubs hardly qualify as a cush drive anyway.

SteveA · Dec 21, 2011

Fullauto said:
Don't think you'll need it with a belt drive. Let's face it, the hard lumps of whatever it is they use in standard Norton hubs hardly qualify as a cush drive anyway.

Belts do not have any shock absorbing effect.....according to those I have asked....

Norman White has produced them in the past, so I assume he saw a need at some point, probably in non standard applications. Don't forget that in my Rickman hub there is no attempt at cush drive. Steve Maney does a cush drive for use in mainly Seeley Nortons, Kenny Cummings for example runs one with a belt and went that way after frame breakages.

My real need is to give my old frame an easier life, it has a couple of cracks already that will be repaired, but I am not ready to go to a replica frame, or the project actually has no point.

Steve

Tintin · Dec 21, 2011

SteveA said:
Does anyone use a Cush Drive in their engine pulley with a belt drive.

The closest think I'm aware of to a cush drive together with a primary belt drive is the engine sprocket of a 1981(?) HD Sturgis. I think it retained the compensation mechanism of the original primary chain setup.

Common Norton practise is to run belt drives without a cush drive - even if that means kicking out the original cush drive of the Dommies. Looking at the kind of damages I've seen and experienced that is a really bad idea and I agree that there is no cushioning in a belt worth mentioning - so if you go ahead please share your designs. It is on my list of things which I'd like to have and maybe design but that list is far to long.

Master Comstock - how about a new project? ;-)

Tim

comnoz · Dec 21, 2011

Tintin said:
SteveA said:

Does anyone use a Cush Drive in their engine pulley with a belt drive.

Click to expand...

The closest think I'm aware of to a cush drive together with a primary belt drive is the engine sprocket of a 1981(?) HD Sturgis. I think it retained the compensation mechanism of the original primary chain setup.

Common Norton practise is to run belt drives without a cush drive - even if that means kicking out the original cush drive of the Dommies. Looking at the kind of damages I've seen and experienced that is a really bad idea and I agree that there is no cushioning in a belt worth mentioning - so if you go ahead please share your designs. It is on my list of things which I'd like to have and maybe design but that list is far to long.

Master Comstock - how about a new project? ;-)

Tim

Believe it or not -it is on the drawing board. Just not something that is going to happen very soon- if at all.

Generally speaking I have not seen much need for a cush-drive unless one is running a lightweight crank. When the crank is light the primary drive and clutch has to absorb a lot more punishment.

With my fuel injection project I use a crank sensor with 30 or 60 teeth. With a computer I can see the crankshaft velocity at any point during each revolution. I have been shocked by how much difference there is in crank speed between 90 degrees after TDC and 90 degrees before TDC. As the crank gets lighter this difference gets much larger especially at lower engine speeds. It shows me why I used to tear up primary drive chains when I used them with a lightweight crank. Jim

Hobot · Dec 21, 2011

Belts transmit tension shock loads about like hydraulics do compression shocks. There is a way around hub cushions and that is via a tensioner on the belt that can take up snatch loads. I've seen these in the slack side or the pull side of belts in various high load applications. I agree there is not much cushion in the factory type set ups, especially after a few hi load rpms that chew up about any re-enforced cushion put in.

One of many many designs to ponder

comnoz · Dec 21, 2011

hobot said:
Belts transmit tension shock loads about like hydraulics do compression shocks. There is a way around hub cushions and that is via a tensioner on the belt that can take up snatch loads. I've seen these in the slack side or the pull side of belts in various high load applications. I agree there is not much cushion in the factory type set ups, especially after a few hi load rpms that chew up about any re-enforced cushion put in.

One of many many designs to ponder

For something like that to be effective you would need one on each belt run- linked together and dampened. The hard part is the fact that you would need around 2 inches of belt deflection to have the needed travel. Space becomes a problem when you consider the minimum bend radius of the belt. Jim

SteveA · Dec 21, 2011

Believe it or not -it is on the drawing board. Just not something that is going to happen very soon- if at all.

Generally speaking I have not seen much need for a cush-drive unless one is running a lightweight crank. When the crank is light the primary drive and clutch has to absorb a lot more punishment.

Hmmm...Jim I have a lightweight crank...

A design already exists, Norman White has made some, and will make me one, at a one off price....if we can generate enough interest then it could help all who plan to run lighweight cranks....?

Hobot · Dec 21, 2011

I don't know how much tensioner/belt slack is needed to work in our low rpm poppers but don't toss out the concept completely off hand keeping in mind its possible to have drive chain tensioner in addition to primary that just might be enough to get away with before yours in invented and installed. I've found belt size-strength to handle our cams in case space but that's as far as I got so far.

http://www.gates.com/file_display_commo ... le=MTZ.pdf

metal links has a very high stiffness and minimal
damping characteristic. This leads to an
inability to resist high dynamic shock loads
without wear and irreversible elongation.
Chain elongation caused by wear over time
(up to 10 times more than a belt) is very critical
to emission control. An example for this
behaviour is given by the use of timing belts
in ”unit injector“ diesel engines. On such
high dynamic, highly loaded systems, chain
technology cannot compete with timing
belts.

Tintin · Dec 21, 2011

comnoz said:
Believe it or not -it is on the drawing board.

Welcome to the club! :mrgreen:

Just not something that is going to happen very soon- if at all.

Welcome to the club!

Generally speaking I have not seen much need for a cush-drive unless one is running a lightweight crank.

I'd dare to disagree slightly after inspecting the gear wheels of the three Commando gearboxes I dismantled recently. They looked much worse than the ones in my Atlas and those were already leading a hard live. IMHO this drivetrain is so much on the edge it needs as much TLC as it can get including a decent cush drive. The cush drive hub is not really decent.

I have been shocked by how much difference there is in crank speed between 90 degrees after TDC and 90 degrees before TDC.

Yes, torsional vibration is a really nice playground, isn't it? We're running 1deg-resultions on our TV sensors, it's pretty amazing what kind of tango is going on there.

Tim

comnoz · Dec 21, 2011

Yes, torsional vibration is a really nice playground, isn't it? We're running 1deg-resultions on our TV sensors, it's pretty amazing what kind of tango is going on there. [quote Tim]

Yep, And that is why the cam gears I have been working on have not made it to market. Jim

rotorwrinch · Dec 21, 2011

I have a dampening sprocket on a Commando framed race bike that uses a 8mm pitch belt. It will be the second week of Jan before I pull the bike out of the toyhauler. I will be taking the assembly off to reverse engineer the work we did years ago. About the time I do that I will no doubt find drawings around here. Production racers had a damping mechanism with the primary drive chain sprocket . You reading this thread Ken Canaga?

If you can wait about three weeks, I can provide so photos, measurements. Just getting back in the swing stateside after being consumed by other activities for the last couple of years.

ATB,
Rj

willh · Dec 21, 2011

A cush engine sprocket at a decent price would be way better than what RGM are asking for cush baskets. If the cost was reasonable I'd be in for one. Thought about adapting a BSA set-up but....

lcrken · Dec 21, 2011

rotorwrinch said:
I have a dampening sprocket on a Commando framed race bike that uses a 8mm pitch belt. It will be the second week of Jan before I pull the bike out of the toyhauler. I will be taking the assembly off to reverse engineer the work we did years ago. About the time I do that I will no doubt find drawings around here. Production racers had a damping mechanism with the primary drive chain sprocket . You reading this thread Ken Canaga?

If you can wait about three weeks, I can provide so photos, measurements. Just getting back in the swing stateside after being consumed by other activities for the last couple of years.

ATB,
Rj

Indeed I am, RJ. I've been trying to find the pictures I took of the cush drive engine sprocket some years ago. If I can't find them, I'll take some new ones to post (if I can find the sprocket!).

As I recall, Norton tried it briefly on some of their race bikes. My memory is a bit vague on the details, but I think I got it from someone associated with the Norton US flat track effort, maybe Jim Massey, one of the NVT team engine guys.

Ken

Tintin · Dec 21, 2011

willh said:
A cush engine sprocket at a decent price would be way better than what RGM are asking for cush baskets.

Which of the RGM belt drives has a cush drive in the basket? I have a belt drive which AFAIR was bought by the guy who sold me my Atlas and he claimed it is a RGM unit (with a totally unsuitable AT10 belt). That meant changing the Dommie main to a Commando main and thus no cush drive at all anymore. I'd be positively surprised if the situation has changed there.

Tim

willh · Dec 22, 2011

Tintin said:
willh said:

A cush engine sprocket at a decent price would be way better than what RGM are asking for cush baskets.

Click to expand...

Which of the RGM belt drives has a cush drive in the basket? I have a belt drive which AFAIR was bought by the guy who sold me my Atlas and he claimed it is a RGM unit (with a totally unsuitable AT10 belt). That meant changing the Dommie main to a Commando main and thus no cush drive at all anymore. I'd be positively surprised if the situation has changed there.

Tim

was looking at the Rimoldi Surflex at 400pounds, but after checking the photo, it is for chain-drive not belt...

pouchy750 · Dec 22, 2011

Duncan Craig ( Seattle WMRRA) is running a Norman White crankshaft cush drive pulley on his Weslake belt drive racer.
But he has stated to me that it is a one off item.
Although NW makes them for him when he requests a new one.

I broke belt drives & Quaife gears constantly until I put a Grimeca cush drive hub on the race bike. And I treat gearchanges with respect, no clutchless shifts.

pouchy750 · Dec 22, 2011

Any chance of a you tube video of this crankshaft vibration?

SteveA · Dec 23, 2011

pouchy750 said:
Duncan Craig ( Seattle WMRRA) is running a Norman White crankshaft cush drive pulley on his Weslake belt drive racer.
But he has stated to me that it is a one off item.
Although NW makes them for him when he requests a new one.

I broke belt drives & Quaife gears constantly until I put a Grimeca cush drive hub on the race bike. And I treat gearchanges with respect, no clutchless shifts.

All of these comments prove I am not crazy to want to do this, thanks guys.

Norman definately has a Norton design and a one off price, and understands my desire for a 1.75:1 ish primary ratio with 40 teeth. That may be why its is a one off item as others might want different ratios. All I can say to that is that the works used 1.76:1 which is standard Commnado triplex drum (57) with 33 tooth triplex engine sprocket, so it will work fine for me and should be sensible for most race bike applications.

I raced my bike with this primary ratio using a Quaife 4 speed cluster, a manx style layshaft bearing, no kickstart, and di not take the cover off the box in 4 seasons. That original layshaft broke some 25 or more years later, but that rider has also broken a TTi 5 speed and accepts he is hard on equipment.

My frame is an original Rickman so today 36 years old and has a crack that needs repairing, so as well as the transmission I want to give the frame an easier time too. And the Rickman hub has no cush drive at all let alone a poor one.

Hopefully RJ and/or Ken can find some pictures or drawings and we can progress this

swooshdave · Dec 23, 2011

Why can't you just use a rear hub with a cush?

Cush Drive Crankshaft Pulley

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