Topic: Plastic rear sprocket?!? Kawasaki 400

[Tugboat]

So I recently sold a 1977 KZ400D4 to a buddy of mine. I had bought it off another friend who moved out of state with the intentions of fixing it up, but between my '76 KZ400 & my CB750 I've got my hands full with projects.

When we got it up in the truck (and at eye level) I noticed that the rear sprocket was solid black, and come to find out it's made out of plastic or nylon or something!!! I'd ridden it to work a few times last year but had never noticed. So, anyone ever heard of such a thing, or know why you would use a non-metal drive sprocket?! I found this on ebay but it's the closet I could find.

http://www.ebay.com/itm/KAWASAKI-H1-500-KH500-NEW-REAR-Nylon-Sprocket-/160350433289?pt=Motorcycles_Parts_Accessories&hash=item2555a17009&vxp=mtr

[CycleRanger]

Nylon is quieter, lighter, and is easier on the chain than metal.
Otherwise, imo, it's inferior in every other way.

My '74 Ford 302 V8 had a nylon-toothed aluminum timing sprocket.
It wore out and jumped a tooth after about 70K.
Not one of Fords better ideas.

[greasymoose]

My gut reaction would be that they did it mostly for quietness. The 400/440s changed over to belt drive sometime around '80, so it goes to show where Kawi's intentions were at the time!

It reminds me of the old Iron Duke Pontiacs with the micarta cam gears. They were nice and quiet...and cracked and failed around 70k miles.

[iya0yas]

Unless you're the original owner I would assume it's an aftermarket sprocket.  Most Nylon blends are hygroscopic (absorb moisture) and as a result loose their dimensional stability.  Nothing new here so I assume the Kawasaki engineers were aware of this attribute and would not have likely assumed such liability vs. saving a few ounces in weight and perhaps 1dBA or less reduction in noise...just my 2 cents...

[Sam Green Racing]

Living in the UK we have slightley different models but the smaller bikes were belt driven, so I guess it's a belt wheel and not a sprocket.

Sam.

[somesuch]

I had two cb750s that had the black nylon sprockets when I bough them. I rode both of them a bit.  Seemed like both sprockets had a tendency to become loose on the four mounting studs, and tended to "ovalize" their mounting holes no matter how often I tightened the four mounting nuts. the teeth seemed to hold up, but again, I did not put that many miles on them.

[faux fiddy]

I did an old volvo timing set that was made of bakelite- similar stuff, maybe better for that application.

Weird timing setup on that old thing.

[MoMo]

Foggy recollection is the plastic sprocket was stock...Larry

[754]

 I remember plastic sprockets for CB 750, I remeber a mag teast where they were dumping the clutch, and it started loosing teeth! Then as they put it, it was like popcorn popping off it, when they all let go... The seemed to hold up under sane use.. they may have been called M.E.P. sprockets..