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Author Topic: Plastic Sprocket?  (Read 1813 times)

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CDN Marvin

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Plastic Sprocket?
« on: April 24, 2006, 07:21:37 PM »
I changed the rear sprocket on my 74 750.  The sprocket that was on the bike was some sort of black plastic.  It is pretty light, and flexes slightly when bent by hand.  I have never heard of plastic sprockets for street bikes.  Does anyone have any knowledge on these?  It seemed to be wearing fairly good.
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texian_biker

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Re: Plastic Sprocket?
« Reply #1 on: April 24, 2006, 08:44:10 PM »
They were an emerging technology in the early 70's, mostly on dirt bikes, then simply vanished as aluminum sprockets became dominant.  long term i don't thing plastic and chain lubes coexisted very well.  I'd be inclined to either trash it or hang it on the wass as a museum piece...JimJ
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CDN Marvin

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Re: Plastic Sprocket?
« Reply #2 on: April 25, 2006, 12:49:13 AM »
Thanks for the info.
There was no way I was going to use it after I saw it was plastic.  I am suprised that it is in such good shape.
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theunrulychef

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Re: Plastic Sprocket?
« Reply #3 on: April 25, 2006, 05:09:45 AM »
I wonder if they could make a modern plastic sprocket that would stand up like steel?  I would think that with some of the advances in polymer technology, this would be feasible, although cost prohibitive.  It's too bad we don't have a wealthy mad scientist sugar daddy here on the boards.  ;D
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Offline MRieck

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Re: Plastic Sprocket?
« Reply #4 on: April 25, 2006, 05:10:36 AM »
 NEP made those. I twisted one into a pretzel.
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Offline dusterdude

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Re: Plastic Sprocket?
« Reply #5 on: April 25, 2006, 05:35:47 AM »
makes you wonder if the style of chain and/or the stresses put on the sprocket make it unadvisable.consider the auto manufactueres have been using nylon encased sprockets on cam gears for a lot of years,they would usually go at least 100,000 miles before needing replacement.
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Offline hcritz

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Re: Plastic Sprocket?
« Reply #6 on: April 25, 2006, 08:35:01 AM »
Hey CDN...
I first say the plastic sprockets in the late 70s...while I was racing moto-cross. We raced in a sand pit and chain and sprocket life was SHORT!!! the dealer told me to try the plastic ones...though he was nuts....The damn things lasted forever!!! AND the chains lasted 3 to 4 time longer too! I was amazed!
Never broke one or even a tooth off of one...and they went through HELL! I raced 250 class..so they took a pretty good beating.
They are also a lot quieter...Would be interesting to see on made now with the new glass filled resins...might make some of that chain noise go away...
I'm still amazed that the toothed belts hold up on Harleys!
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Offline MRieck

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Re: Plastic Sprocket?
« Reply #7 on: April 25, 2006, 08:41:25 AM »
Quote from: hcritz on April 25, 2006, 08:35:01 AM
Hey CDN...
I first say the plastic sprockets in the late 70s...while I was racing moto-cross. We raced in a sand pit and chain and sprocket life was SHORT!!! the dealer told me to try the plastic ones...though he was nuts....The damn things lasted forever!!! AND the chains lasted 3 to 4 time longer too! I was amazed!
Never broke one or even a tooth off of one...and they went through HELL! I raced 250 class..so they took a pretty good beating.
They are also a lot quieter...Would be interesting to see on made now with the new glass filled resins...might make some of that chain noise go away...
I'm still amazed that the toothed belts hold up on Harleys!

I think belts staying on Top Fuel blowers is more amazing. ;)
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Offline crazypj

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Re: Plastic Sprocket?
« Reply #8 on: April 25, 2006, 08:47:24 AM »
I seem to remember the main problem wasnt the teeth but the mounting bolts
PJ
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Offline hcritz

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Re: Plastic Sprocket?
« Reply #9 on: April 25, 2006, 08:56:51 AM »
Hey MRieck...
Sometimes they don't...usually with spectacular results!<G>
I forget the horsepower that the blower on those things soak up at top RPM...but it's a BUNCH!!!

Hey PJ...I VAGUELY remember mine having steel inserts where the sprocket bolted on...
Never had a problem...
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CDN Marvin

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Re: Plastic Sprocket?
« Reply #10 on: April 25, 2006, 09:34:16 AM »
The one I have doesn't have metal inserts, and it has very slight depressions on the back side where is mounts to the hub.  On the front there is that metal guard ring, so the pressure is spread out.
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Offline MRieck

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Re: Plastic Sprocket?
« Reply #11 on: April 25, 2006, 09:40:20 AM »
Quote from: hcritz on April 25, 2006, 08:56:51 AM
Hey MRieck...
Sometimes they don't...usually with spectacular results!<G>
I forget the horsepower that the blower on those things soak up at top RPM...but it's a BUNCH!!!

Hey PJ...I VAGUELY remember mine having steel inserts where the sprocket bolted on...
Never had a problem...
Takes about 250HP to drive them. The NEP sprockets I used had no inserts. NEP still makes cruise controls (probably with the same material).
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Offline hcritz

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Re: Plastic Sprocket?
« Reply #12 on: April 25, 2006, 10:18:35 AM »
Hey Marvin...
Any difference in chain noise with the plastic???
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CDN Marvin

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Re: Plastic Sprocket?
« Reply #13 on: April 26, 2006, 09:36:44 AM »
I haven't gone for a ride since I changed to the alloy one.  It has aftermarket 4 into 2 exhaust that is loud enough to drown out any noise quieter than a gun shot, but I hope to find out later today.
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