Keeping chain out of spokes???

GoldenMotor.com

meowy84

Member
Jul 18, 2009
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Canada
Being of the school that an ounce of prevention is worth a pound of cure, has anyone experienced the engine drive chain jumping off the rear sprocket and getting tangled in the spokes with disastrous (and painful!) results?

I'm assembling my kit and have all other safety issues pretty much ironed out but this scary scenario is keeping me awake at night. Let's face it, even with the chain properly tensioned we're still dealing with a rubber mounted rear sprocket and engine-to-frame clamps that could cause the engine to twist upsetting the sprocket alignment causing the chain to break or jump off. And if the chain decides to jump toward the sprockets, well......ouch!

Has anyone come up with solutions? I thought of making a fairly large (larger than the sprocket) diameter sheetmetal disc to go betweem the sprockets and the sprocket so if the chain jumps it doesn't rip the spokes out making you fall on your a$$. Any other ideas?
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
The trick to keeping the chain 'out of your spokes' is to keep it on the sprocket in the first place...
First, you need to make sure the sprocket is mounted so that it's as close to perfectly centered as possible & has no 'side to side' wobble. (It also helps to file the sides of the sprocket teeth so that they can 'feed' into the chain without catching the sides of the links & causing the chain to snag & derail.
It's also very important that the tensioner feeds the chain straight onto the sprocket & then put a screw through the tensioner into the frame rail to keep it from ever moving.

Follow these steps & you will be okay! ;)

Also... don't use rubber mounts on the engine! bolt it as solid as possible so that it can't ever move!

I've built hundreds of bikes all with the stock parts & I've had very few problems with the chains. ;)
 
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meowy84

Member
Jul 18, 2009
239
0
16
Canada
Thanks for the info. I've already done the things you mentioned like the screw through the tensioner into the frame rail. I've also upgraded the engine mounting hardware with posi-lock nuts and liberal use of thread locker. In addition I've also used the same screw thru frame idea on the engine straps to minimize engine twisting.

As for the rear sprocket that's a great idea and I'll definitely be filing the teeth sides a little. As for the sprocket wobble no matter how I do the tightening it's virtually impossible to get it to mount without any runout (no doubt because of the rubber fibre discs which are definitely less than ideal solution). I tried using my dial gauge which was overkill so I gave up since the lowest runout I've been able to get is roughly somewhere between 1/16"-1/32" which is huge when you really think about it.
 

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
Although I like to see a sprocket with absolutely no runout, 1/16 to 1/32" isn't really that much. In fact it's probably better than most. That's for lateral runout. As for concentricity to the hub there should be no reason why you can't get that down to zero. It takes some work and patients but centering the sprocket on the hub is essential.

Maybe the sprocket is bent. This is not uncommon. Lay it on a known flat surface, a sheet of glass is the best, and check that the sprocket itself isn't warped/bent. If you find that it is you can work it flat by using several means such as a hammer, a large Cresent wrench or whatever tool you can find to get the warp out of the sprocket. If you don't feel comfortable doing that, replace the sprocket with one that is flat.
I've had several kit sprockets that had a warp and was able to straighten them with a little work.

While you have the sprocket off check the rubber donuts to make sure they are of consistant thickness. I've encountered them that were noticably of different thicknesses across their face. If that's the case a side grinder, or a drill motor with a course sanding disc can be used to work the rubber into the proper thickness. (sand off the high spots)
Good luck, keep us informed.
Tom
 

meowy84

Member
Jul 18, 2009
239
0
16
Canada
Thanks 2door. I did check the sprocket before mounting and it was nice and flat so that's a blessing and the hole for the hub was also stamped smack in the middle of the sprocket. (I wonder if anyone has had a stock sprocket with the hole stamped off center on these things?) Anyways, I did check the concentricity to the hub which is perfect as well. In fact when I went to mount the sprocket out of the box it was slightly tight on the hub so 2 quick careful passes on the inside with a file made it fit the hub perfectly.

So it's just the side-to-side runout that's the issue and I think the discs are the culprits. They were of uniform thickness but not uniform composition. Looking at the side cross-sections one of the discs looks like plain rubber whereas the other has some fibers embedded in it. So I think the discs would compress differently. And to get the sprocket to the current runout not all of the bolts are tightened to the same torque. Some I had to tighten more and some less no doubt because of how differently the discs compress.
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
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Littleton, Colorado
Meowy,
You should be good with the run out you have now. Keep a watch on it and the bolt torque after a few miles. The difference in rubber composition isn't uncommon. That's just Chinese QC. :)
And yes, I've seen a sprocket that the center hole was nearly 1/4" out of center. Now that one would have caused some problems. Sad thing is there are guys who would not see it and try to run it on their bike then come here and ask why their chain keeps coming off. And that's a fact.
Tom
 

meowy84

Member
Jul 18, 2009
239
0
16
Canada
Thanks for the tips and info gentlemen. :) Can't wait to get this thing finally running. It's been almost 2 years since I actually got the kit, just rarely have time to work on it. But it's in the home stretch now. Chains, carb and controls it all that is left to install.