Vertical Wobble in Clam Shell Hub

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Msiert

Msiert

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Sep 19, 2014
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Just got done last week putting my bicycle kit together and been doing a little riding got about 5 hours on it so far...boy do I get a lot of thumbs up!

I do have a question though, I found that the chain tightness changes when I turn the rear wheel 180 degrees, it goes from 1/2" slack to 3/4" to an inch slack in a half turn of the sprocket. I'm thinking that this is a vertical wobble in the rear sprocket but how could a sprocket with a clam shell hub not be perfectly centered in the wheel? But may be it's something else?

Being a novice at this can anyone give me any pointers to fix this or is this not something to worry about?
 
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maniac57

maniac57

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Possibly a bent axle, mis-machined hub adapter, cheap hub, off center sprocket. You need to find the problem.
Getting the rear sprocket perfectly centered is a MUST for a reliable driveline.
 
Msiert

Msiert

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Not having tensioner have anything to do with it?

By not running a tensioner have anything to do with it? If I hold my finger on the bottom chain with a little pressure like a tensioner would do then there is no difference in tension at the 180 degree turns of the rear sprocket.

Today I check the trueness of the rear sprocket and clutch sprocket
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and they were both perfect no wobble at all and I check the alignment of the two sprockets and that was right on (a few days ago I has spent a bunch of time on that) so no adjustments were needed.

About the only thing that I did that might have helped was making sure the rear wheel was put on straight by giving it a straight and strong pull back so the peddle chain was at the correct tension and tightening the wheel nuts then I adjusted the drive chain tension with the engine mount bolts.

It's a little better but I still have tension difference at the 180 deg movements.
 
Msiert

Msiert

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Update:
Found that the rear wheel's hub was not centered. Plan to pull the wheel and sprocket and take it to a bike shop to true when winter sets in.
 
2door

2door

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Msiert said:
Update:
Found that the rear wheel's hub was not centered. Plan to pull the wheel and sprocket and take it to a bike shop to true when winter sets in.
Click to expand...
Just FYI, the hub being centered in the rim has nothing to do with the sprocket/hub concentricity. You could remove the spokes and rim and it wouldn't change how the sprocket attaches to the hub.

Just curious but how did you check to see if the sprocket is centered on the hub? What method did you use? I'd also like to know what brand of "clam shell" sprocket adapter you have. My gut feeling is it might be the culprit here.

I'm also a little concerned where you say you adjusted drive chain tension by using the engine mount bolts. The engine shouldn't move. It should be secured to the frame so there is absolutely no movement. Chain tension is then adjusted by either moving the rear axle in the drop outs or a chain tensioner. Loosening or tighteneing the engine mount fasteners isn't the way to adjust chain tension.

Tom
 
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Msiert

Msiert

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Omaha NE.
2door said:
Just FYI, the hub being centered in the rim has nothing to do with the sprocket/hub concentricity. You could remove the spokes and rim and it wouldn't change how the sprocket attaches to the hub.

Just curious but how did you check to see if the sprocket is centered on the hub? What method did you use? I'd also like to know what brand of "clam shell" sprocket adapter you have. My gut feeling is it might be the culprit here.

I'm also a little concerned where you say you adjusted drive chain tension by using the engine mount bolts. The engine shouldn't move. It should be secured to the frame so there is absolutely no movement. Chain tension is then adjusted by either moving the rear axle in the drop outs or a chain tensioner. Loosening or tighteneing the engine mount fasteners isn't the way to adjust chain tension.

Tom
Click to expand...
Please refer to post below.
 
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Msiert

Msiert

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2door said:
Just FYI, the hub being centered in the rim has nothing to do with the sprocket/hub concentricity. You could remove the spokes and rim and it wouldn't change how the sprocket attaches to the hub.

Just curious but how did you check to see if the sprocket is centered on the hub? What method did you use? I'd also like to know what brand of "clam shell" sprocket adapter you have. My gut feeling is it might be the culprit here.

I'm also a little concerned where you say you adjusted drive chain tension by using the engine mount bolts. The engine shouldn't move. It should be secured to the frame so there is absolutely no movement. Chain tension is then adjusted by either moving the rear axle in the drop outs or a chain tensioner. Loosening or tighteneing the engine mount fasteners isn't the way to adjust chain tension.

Tom
Click to expand...
Tom,

I bought the bike and engine kit that included clam shell hub sprocket from Phantom Bikes. They have an engine mount that has slots in it for the 4 bolts that fasten into the bottom of the engine. On the engine mount there is a bolt that allows you to slide the engine forward to tension the chain and then you tighten the 4 bolts that go through the engine mount to the engine.

http://phantom-bikes.com/shop/motorized-bicycles/phantom-ghost-diy-kit.php

I tested using zip ties mounted to the frame to check the rotation on the rear hub sprocket and the sprocket on the clutch and they looked perfect with no trace of vertical wobbly and I was lost to what the problem could be.

Then I called Phantom Bikes and told them about the problem and they said that they were aware of the problem that if you look close the rear wheel peddle sprocket has a small wobble and they have contacted their supplier of the wheels. I took this to mean the hub itself was out of center and it could be corrected by Turing the wheel.

What still confuses me is how could the rear peddle sprocket have a vertical wobble and the rear drive sprocket I tested does not. I talked to a friend that does a lot of work on his bikes about it this afternoon and he said Turing the wheel would not change the centering of the hub. But in my mind if the spokes on one side being one length and the spokes on the other side being another length would give the hub a wobble?
 
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S

Slogger

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Sep 8, 2014
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When I was putting my bike together I ran into this. It was so bad it was making the chain make a 'ping' as it came off each tooth. The back wheel wasn't on straight. It doesn't take much crooked to do this, either.

If everything is straight and true, then something else must be out of whack, I'd guess the sprocket adapter. If it's machined poorly you should be able to see the run-out if you look close. If it isn't there, try a different chain if you can get one.
 
2door

2door

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As I , and your friend say, trueing the wheel will have no effect on if the sprocket is centered on the hub. The outer rim/spokes have nothing to do with how the sprocket and the adapter is attached to the rear hub. Your friend is right.

From your description it sounds as if you have a 4 stroke engine and not a 2 stroke Chinese kit. Correct? If so, yes, drive chain tension can be adjusted by moving the engine on the mount. Nevertheless, the rear sprocket must be concentric with the rear hub. If your supplier is aware of a problem you should let them take care of it for you. It sounds to me as if the adapter or their sprocket is indeed the problem.

I suggest you post a photo of your installation. That would allow us to see what you're dealing with.

Tom
 
Msiert

Msiert

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I've had the rear wheel off a number of times and the last time I was careful to pull the wheel back straight but it is still something I did by feel and sight. I guess I could check the measurement from the end of each side drop outs to see if it's the same.

After putting a zip tie on the rear frame arm an 1/16" over the teeth of the rear sprocket and spinning the wheel it was perfect no vertical wobbly. Did the same on the transmission sprocket and it was perfect too.

I did not check for a horizontal wobbly. Guess a horizontal wobbly would give you the same tight/loose chain symptoms as a vertical wobble and installing the rear wheel not perfectly straight would cause a horizontal wobble

Still Phantom Bikes admitted that the wobble was a know problem that they are addressing with the manufacture. I might have misunderstood what was the problem and it might have been the clam shell bracket that they were talking about. Not sure what that meant for me because they said that it has not caused any problems....think I am the one that will have to fix the problem since they don't think it's enough of a wobble to cause any problems?
 
Msiert

Msiert

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Sep 19, 2014
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Omaha NE.
Msiert said:
I'll get some pictures posted.
Click to expand...
Here is a picture of my sprocket you can see where I marked the where the chain is tight or loose (T = tight and L = Loose). The double lines (=) is the place in the sprocket where the chain is in a transition from real tight to less tight and the same on the loose side (from real loose to less loose). The range in tension is 1/2" at it's tightest to 1" at it's most looseness.

When the chain is traveling over the transmission sprocket the teeth of the sprocket travel mostly in the center of the chain to drifting towards the inside a little but the sprocket teeth never moves the chain.
 

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2door

2door

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First of all let me congratulate you on a great looking bike/build. Very nice, sir.

It would be interesting to see what happens if you remove the drive chain, suspend the rear wheel so it spins free then use a temporary 'pointer' attached to the frame and with the end of the pointer aligned perfectly with the outer edge of the sprocket teeth.

Slowly rotate the rear wheel and watch the pointer to see how it stays aligned as the wheel turns. If the sprocket is not perfectly centered you will quickly see it as the pointer end moves closer and further away from the outer edges of the teeth.
This will tell you if the problem is the sprocket adapter or something else.

If you see that the sprocket is centered then you might be looking at a bad chain. Either it is binding or it has a kink or twist. You might also want to check the concentricity of the drive sprocket. If it is drilled off center that too can cause a tightening/loosening of the chain. Check how the chain engages the sprocket teeth too. It should settle into the valleys of the teeth equally around the full circumference of the sprockets. If it rides higher in some areas this too can cause your problem.
Let me know what you observe.

Tom
 
maniac57

maniac57

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Also check the hub itself for concentricity. LOTS of newer bikes have off center problems in the hubs and freewheels. Use same process as above to check hub.
 
Msiert

Msiert

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Sep 19, 2014
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Omaha NE.
2door said:
First of all let me congratulate you on a great looking bike/build. Very nice, sir.

It would be interesting to see what happens if you remove the drive chain, suspend the rear wheel so it spins free then use a temporary 'pointer' attached to the frame and with the end of the pointer aligned perfectly with the outer edge of the sprocket teeth.

Slowly rotate the rear wheel and watch the pointer to see how it stays aligned as the wheel turns. If the sprocket is not perfectly centered you will quickly see it as the pointer end moves closer and further away from the outer edges of the teeth.
This will tell you if the problem is the sprocket adapter or something else.

If you see that the sprocket is centered then you might be looking at a bad chain. Either it is binding or it has a kink or twist. You might also want to check the concentricity of the drive sprocket. If it is drilled off center that too can cause a tightening/loosening of the chain. Check how the chain engages the sprocket teeth too. It should settle into the valleys of the teeth equally around the full circumference of the sprockets. If it rides higher in some areas this too can cause your problem.
Let me know what you observe.

Tom
Click to expand...
Thanks Tom, I'll pull the chains and do the tests you recommended and report back with my findings. I'm new to hobby and have found this forum to be a wealth of information. Thank you for all your time in making this forum so great!

maniac57 said:
Also check the hub itself for concentricity. LOTS of newer bikes have off center problems in the hubs and freewheels. Use same process as above to check hub.
Click to expand...
"Hub Concentricity" This is what I think the bike company was saying was off and what I mistakenly thought I could fix by truing the wheel. How would you correct a hub wobble?

I will check for this too....thank you!
 
Msiert

Msiert

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Sep 19, 2014
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Omaha NE.
Well the weather has turned, 60F at noon and 20 by midnight with the next two weeks the lows will be in the teens and highs in the low 30F's.

Going to start the investigation to the wobble durning this cold spell. Been reading up on hubs and found this.

http://m.youtube.com/watch?v=OI6JxL-zjXc

I will be running the test recommended to me but if the above video turns out to be the problem which I'm beginning to think it might be couldn't I could use a shim between the clam shell sprocket and the hub shell to make up for the off milling?

I bought a feeler gauge set thinking I could try different thickness to correct the wobble. Can start of with a shim as thin as .003 and put it between the clam shell and hub shell on the side where the chain is the loosest.

Think this would work?
 
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