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Old 11-29-2008, 03:31 AM   #1
Skippii OP
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What does a Cush Drive do?

What does it do?
How does it work?
Why is it good?
Why do some people not like them?

Pics appreciated.
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Old 11-29-2008, 05:49 AM   #2
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A cush drive is a part of a motorcycle drive-train that is designed to reduce stress from engine torque damaging other components during gear or throttle changes. A common design used by Honda, in particular on the VTR 1000F Superhawk is made of three major pieces: the wheel, the sprocket assembly, and the rubber damper. The wheel and the sprocket assembly fit together with five sections much like two hands woven together. In between the contact of the two assembly are rubber blocks. This makes it so the wheel and the sprocket have a dampening layer between them, and the rubber blocks reduce wear and fatigue of the metal assemblies.
When the rubber damper becomes old and hardens, or wears out, the changes in load on the drive chain instigated by changes in throttle position or changing gear can cause snatchiness in the power delivery. Loads particularly on the drive chain can be massively increased in these conditions, increasing the risk of breakage or of contact with the swinging arm resulting in damage. Perhaps more pointedly the sudden transfer of force to the rear tyre can cause momentary loss of traction (lock or spin) resulting in small changes of direction or at worst total loss of control.




from wikipedia, thank dog for copy- n- paste!!
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Old 11-29-2008, 06:02 AM   #3
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Oh, this thing?


Thanks.
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Old 03-14-2010, 05:30 AM   #4
Zombie_Stomp
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I have been debating over cush drive versus non. I have an XL600 I want to hop up with XR suspension parts. I like the high ride height and the extra performance capabilities and rebuildable rear shock versus the stock non rebuildable one with no reservoir. I want to be able to handle another MOAB and not join into getting a KLR like my friends. The potential licensing/plating issues then are a non issue since XL600s came street legal. There are a lot of reasons.

The only problem is that the XR swingarm only takes the certain non-cush drive hub. if i were a little wealthier, I would spring for this hub from RAd manufacturing or (and i may) get the XL hub turned on a lathe or whatever neccesary if possible to get it to fit.

The XR650L guys and plated XR600 are dealing without the cush drive pretty well I suppose. I have dealt with countershaft wear issues on both cush and non versions of the Honda RFVC engine so i know how to keep that at bay even without it. Using only stock sprockets of softer steel than the countershaft, greasing the splines, continuing to use some variety of knobby as I do usually anyway, and keeping the proper chain tension are parts of that regimen.

The only concern of mine is internal transmission wear. I have seen the pitted 3rd gear prevalent in transmissions on cush and non 600 RFVCs, but i was wondering still. A friend told me it also protects the gears from harmonic vibrations at highway speeds. I know based on what I've seen already that the differences are probably minute if I keep all the above factors in check, but I'm hoping to get the attention of some engineering types in here to tell me what they know. I know about the cushiness upon take off, but I am aware also of the springs in the clutch basket that are there to take care of some of that shock, and after riding an XR650L without cush, I noticed i got used to feathering the clutch a little more and I see the take off and gear change as not much of an increase in wear on the parts. But is the harmonic vibrations thing voodoo, or is it a further valid argument in favor of striving for cush drive? I just want some opinions.
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Old 03-14-2010, 08:17 AM   #5
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IMO on the XR, don't worry about the cush drive. Be a different story on a liter plus sportbike.


On another note is the Burger place still open over by 39th and Sandy in the Hollywood district in NE PDX?
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Old 03-14-2010, 10:58 AM   #6
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I think the cush drive is there to do a job besides absorbing shocks from shifting and drive line lash.

Power pulses from the engine are severe and big lumpy engines are worse - VTR1000 chain life is reduced from the pounding, not because of the fat torque curve.

In the experimental airplane world we learn about this stuff when we hang a propeller on the crankshaft and things start breaking. Long stroke engines like type 1 VW's like to snap off right behind the prop hub. The BD5 had all kinds of trouble because the prop was on the end of a long drive shaft. I've seen instances where people trying to damp out the pounding in their reduction drives had the cush drive bits go to pieces or even melt or go up in smoke.

I've been noodling with the idea of putting a motorbike engine in an airplane for a long time. I'm thinking turbo 'Busa in a Cassutt but I think the clutch and/or tranny would self destruct in short order.

I think if you delete the cush drive you're asking for clutch basket issues, among other things. I would avoid doing it if possible.
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Old 03-14-2010, 04:37 PM   #7
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So why on Earth does the little Ninja 250 have a cush drive? To make it more beginner friendly?
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Old 03-14-2010, 05:00 PM   #8
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Quote:
Originally Posted by DevilNinjaDog
So why on Earth does the little Ninja 250 have a cush drive? To make it more beginner friendly?
Certainly can't hurt the smoothness.
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Old 03-14-2010, 06:11 PM   #9
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Amazing! I didn't know that there was a bike without some sort of cush drive? Most of the cush drives that I have seen are found in the hub of the rear wheel. Some are found in the clutch hubs. Some are found at the end of the engine crank and involve a big spring. As stated by another poster, the cush drive is there to absorb drive train shocks caused by engine combustion. Bikes will not last very long without some sort of cush drive. If the cush drive is not in the rear wheel it will be found somewhere else in the drive train.

If you want to swap in a non-cush drive wheel for one with cush drive, you had better find out where the bike with non-cush drive wheel has its cush drive and add that to your swap. (IMHO-posted as politely as I can)

edit: 50cc honda cubs had cush drive in the rear wheel. As does my 1050 Sprint ST. Some service manuals give a service life to the cush drive and want it replaced on time/distance. Every combustion pulse pounds thru every part of the drivetrain. this alone is enough to destoy parts in short order. Hard shifting, landing jumps, potholes etc are as nothing by comparison.
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ibafran screwed with this post 03-14-2010 at 06:23 PM
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Old 03-14-2010, 06:41 PM   #10
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It's a very simple shock absorber in the drivetrain.
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Old 03-14-2010, 07:40 PM   #11
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Cush

Ask your main sprocket & shaft splines about cush.
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Old 03-15-2010, 05:22 AM   #12
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Quote:
Originally Posted by DevilNinjaDog
So why on Earth does the little Ninja 250 have a cush drive? To make it more beginner friendly?

I don't think the size of the engine matters. A Ninja 250 doesn't have the same size gears, shafts, chain, etc. that a VTR1000 has.

Another factor is the chain drive itself. Motorcycles chains vibrate at every tooth engagement by their very nature: The link pins don't travel in a circular pattern around the sprockets - they impact the valley between the sprocket teeth, then rise slightly before starting a round path. The bigger the sprocket, the less the vibration, but it's still there, causing vertical chain motion and a corresponding accel/decel of the driveline.

A silent chain like a snowmobile has would be better in this regard, but who wants to lug around a huge chain case on their swingarm?
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Old 03-15-2010, 06:00 AM   #13
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Quote:
Originally Posted by ibafran
Amazing! I didn't know that there was a bike without some sort of cush drive? Most of the cush drives that I have seen are found in the hub of the rear wheel. Some are found in the clutch hubs. Some are found at the end of the engine crank and involve a big spring. As stated by another poster, the cush drive is there to absorb drive train shocks caused by engine combustion. Bikes will not last very long without some sort of cush drive. If the cush drive is not in the rear wheel it will be found somewhere else in the drive train.
So where the heck is it on my WR 450 F ??????????????
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Old 03-15-2010, 07:17 AM   #14
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Harleys have them now, too. I retrofitted one onto my '07 Electra Glide; it made a big difference in smoothness, drivetrain noise and comfort.
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Old 03-15-2010, 11:57 AM   #15
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Quote:
Originally Posted by sieg
So where the heck is it on my WR 450 F ??????????????
Not usually cush drives on dirt bikes. Some of the conversions to "motard" or what not involve cast wheels with cush drives.

There are often arguements as to whether a dirt bike is suitable for long distances on road or not part of which involves issues with the increased tire grip and lack of cushioning in the drivetrain.

BMW's even have them in driveshafts.

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