Sprocket "bounce", hub problem?

L

Lucky_7

Member
Hello guys,

I have had an issue with newer sprockets "bouncing" on the hub. I cant tell if it's in the stamped gear, or in the hub. I have also had a theory that a single lock bolt hub doesnt seat straight on the axle. But I haven't been able to test it. The hub is tight sliding on the axle so the bolt "shouldn't" make a difference. Heres the problem.

I can mount a new hub and sprocket, set the chain and the chain runs smooth. After a race, or even just hot laps, I can check the chain and it will be tight on one side, and loose on the other, like the sprocket is off center of the axle. It will normally wobble slightly also. So I have to reset everything, but, if it does it during the race its has to be hurting the overall performance. It's been very frustrating trying to figure out. Any ideas?
 
What I remember experiencing is the holes which the screws go through on the gear are not perfect with the gear screws. You end up with the gear stressed when mounted even though it seems ok. I usually had to make the holes in the gear a little larger to account for slop and things not being perfect. I also usually had to file the edges of the split gear because when it was cut it was not cut perfect and where the two pieces meet on the flat, the flat is not really flat and the two pieces do not butt up evenly. I cleaned stuff up making sure the two gear halfs are mated well and then with the holes opened up I made sure everything went together easily. The nuts will lock things down and the round part of the hub and the round part of the gear usually match up ok. It's the slop in the rest that will cause you issues like your explaining, at least to my memory which is often flawed. ... :)
 
Make sure you put them on the same way every time as well.
Are you getting the chain too tight?
 
XXX#40 said:
Make sure you put them on the same way every time as well.
Are you getting the chain too tight?
Click to expand...

I was thinking the same thing.

Especially making sure you have the gears matched the way they were cut.
Or bent axle.
Or drive gear loose or bent. or stiff links in chain.
 
Most gears are marked/stamped for matching purposes.
This is the most common thing that guys miss.

If that's not it, change the gear and try again - that would rule out being a bad gear or not.
Also, chain links can get twisted, stretched, etc.
If you're using a master link - DON'T.

1 pinch bolt gear hub is not the problem. They've been used successfully for many years.
Now, the hub itself may be bent or something wrong with it.

Axle bent?
The axle and hub can quickly be checked with a dial indicator, (or a straight edge and keen eye.)

Hope that one of these things catches the problem for you.


-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
30 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
These are all good points but here's what i would do.
Firmly mount a dial indicator somehow to the chassis. This may require that you clamp a substantial steel bar across the frame rail with "C" clamps or vise grips.
Measure the radial and lateral runout of the sprocket hub and the axle.
If either is bent replace it.
Not all sprockets have the same ID.
Not all sprocket hubs have the same size shoulder for the sprocket to fit on to.

Inspect the chassis for cracks where the rear crossmember is welded to the left and right frame rails.
 
The cheap gears holes are too large, if you don't get the gear tight enough they can shift
 
"I can mount a new hub and sprocket, set the chain and the chain runs smooth. After a race, or even just hot laps, I can check the chain and it will be tight on one side, and loose on the other, like the sprocket is off center of the axle."


edit up front after writing all the junk below the line: Reading again what you wrote I'm not sure about what the actual problem you see is. You wrote "I can check the chain and it(is >it< the chain or the gear) ... Is the gear getting out of round or is the chain going bad having tight spots develop causing it to tighten and loosen depending on what part of the chain is going around the gear?

The cause of either problem may be just adjusting the chain too tight. Probably every one of us starting out tightened the chain too much thinking it would be better tight then having some slop in it. It just looks right and better when it's tighter then looser no matter how much experience you have. Eventually most get use to feeling the amount of slop in the chain and go by feel. Another thing I just though about is when first installed if you spin it and it seems to make noise or odd noise, it's too tight or the chain needs lubed or cleaned and lubed.


____________________________________________


The problem is not about him not being able to line things up and get the chain running smoothly. He can do that fine. The problem only occurs after the kart comes in off the track. Things change from just fine to not good, while the kart is on the track.

My take is when the gear is initially locked to the axle though it runs free there was some sort of bind put into the mounting of the gear and using it on the track causes it to shift.

Another thing I just thought about now is maybe heat build up on the track and expansion of parts is causing the problem? Again unless there was a bias when put together in one way or another heat build up would make things expand sort of equally. But maybe not.

Another thing I just thought about now is maybe the chain is being installed to tightly for the amount of chassis flex while out on the track and the twisting chassis is both heating things up and forcing the axle gear out of alignment. Maybe the solution is as simple as putting a little more slack in the chain?

He does not indicate he has any problem at all initially lining things up.




I have a question for the starter of this thread. You said you can line things up ok with new gears. But when it comes off the track something gets out of round. My question is can you again line up the 'same' gears and they will be ok until the next time you come off the track?

Or do you have to put new gears on again to get it to line up?

If when it comes in the old gears are now junk. Look closely at them to see what about the gear changed. Again maybe the chain being too tight and chassis flex is bending your gears?
 
XXX#40 said:
Make sure you put them on the same way every time as well.
Are you getting the chain too tight?
Click to expand...

I do not think the chain is to tight on initial install, but, if you have a recommendation for how tight it should be i'll take that opinion and try it.

One Fast Kat said:
I was thinking the same thing.

Especially making sure you have the gears matched the way they were cut.
Or bent axle.
Or drive gear loose or bent. or stiff links in chain.
Click to expand...

Axel isn't bent, I could use and indicator to confirm, however, i have been a machinist for 15 years and have keen eye on bent bar stock.

flattop1 said:
What kind of chain? Low quality chain is a problem.
Clutch drivers cause that exact problem also.
Click to expand...

I believe we are running RLV Extremes...Not sure how high those rank.

CarlsonMotorsports said:
Most gears are marked/stamped for matching purposes.
This is the most common thing that guys miss.

If that's not it, change the gear and try again - that would rule out being a bad gear or not.
Also, chain links can get twisted, stretched, etc.
If you're using a master link - DON'T.

1 pinch bolt gear hub is not the problem. They've been used successfully for many years.
Now, the hub itself may be bent or something wrong with it.

Axle bent?
The axle and hub can quickly be checked with a dial indicator, (or a straight edge and keen eye.)

Hope that one of these things catches the problem for you.


-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
30 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Click to expand...

Yes gears are matched and kept matched, all gears do it on the same hub. New hub will normally be better but eventually it will start the same symptoms. No master links. I can reinstall the same gear and it will be perfect. After the race it will be out of round again.

Jimbo said:
These are all good points but here's what i would do.
Firmly mount a dial indicator somehow to the chassis. This may require that you clamp a substantial steel bar across the frame rail with "C" clamps or vise grips.
Measure the radial and lateral runout of the sprocket hub and the axle.
If either is bent replace it.
Not all sprockets have the same ID.
Not all sprocket hubs have the same size shoulder for the sprocket to fit on to.

Inspect the chassis for cracks where the rear crossmember is welded to the left and right frame rails.
Click to expand...

These are new karts so I can look at the chassis but it seems unlikely they are cracked. I will probably check the hub with an indicator as I have found wheel hub faces to be "not square" to hub axis. If that makes an sense....

paulkish said:
"I can mount a new hub and sprocket, set the chain and the chain runs smooth. After a race, or even just hot laps, I can check the chain and it will be tight on one side, and loose on the other, like the sprocket is off center of the axle."


edit up front after writing all the junk below the line: Reading again what you wrote I'm not sure about what the actual problem you see is. You wrote "I can check the chain and it(is >it< the chain or the gear) ... Is the gear getting out of round or is the chain going bad having tight spots develop causing it to tighten and loosen depending on what part of the chain is going around the gear?

The cause of either problem may be just adjusting the chain too tight. Probably every one of us starting out tightened the chain too much thinking it would be better tight then having some slop in it. It just looks right and better when it's tighter then looser no matter how much experience you have. Eventually most get use to feeling the amount of slop in the chain and go by feel. Another thing I just though about is when first installed if you spin it and it seems to make noise or odd noise, it's too tight or the chain needs lubed or cleaned and lubed.


____________________________________________


The problem is not about him not being able to line things up and get the chain running smoothly. He can do that fine. The problem only occurs after the kart comes in off the track. Things change from just fine to not good, while the kart is on the track.

My take is when the gear is initially locked to the axle though it runs free there was some sort of bind put into the mounting of the gear and using it on the track causes it to shift.

Another thing I just thought about now is maybe heat build up on the track and expansion of parts is causing the problem? Again unless there was a bias when put together in one way or another heat build up would make things expand sort of equally. But maybe not.

Another thing I just thought about now is maybe the chain is being installed to tightly for the amount of chassis flex while out on the track and the twisting chassis is both heating things up and forcing the axle gear out of alignment. Maybe the solution is as simple as putting a little more slack in the chain?

He does not indicate he has any problem at all initially lining things up.




I have a question for the starter of this thread. You said you can line things up ok with new gears. But when it comes off the track something gets out of round. My question is can you again line up the 'same' gears and they will be ok until the next time you come off the track?

Or do you have to put new gears on again to get it to line up?

If when it comes in the old gears are now junk. Look closely at them to see what about the gear changed. Again maybe the chain being too tight and chassis flex is bending your gears?
Click to expand...

Yes, I can line up the same gears and normally it will be fine. One very important note is that the hub, also seems to wobble or bounce after the race. Like it to has been effected during the run. So the process would include loosening and resetting the hub first, then remounting gears, set chain, everything looks good, make a run or two, and the chain will now be tight on one side of the sprocket and extremely loose on the other.



The chassis flex is a very good point. I set the chain to what I think is a good deflection amount. I could see that amount being taken up with the flex. Maybe the chain is to tight and with that it moves the sprocket constantly under stress. I can definitely see it causing handling issues also if the chain is binding up the chassis.
 
Still think the chain maybe too tight. Off the top of my head and others can correct me if I'm wrong, you should be able to 'easily' move the chain in the center between the two gears an inch up and down.

Another though not yet offered. Maybe your alignment between the axle gear and the clutch gear is off?

Maybe your engine is not mounted squarely making the clutch gear a little off?

Again when you spin it even if it's perfectly lined up and it sounds sort of odd or really different then if you'd put just a little more slack in it, it's probably too tight.
 
RLV chain is adequate.
Clutch driver can be bad.
New chassis , ok . What brand motor mount?
Hub getting knocked out of round or wobbling , then an readjustment fixs it ? That sure don't seem right. Bent is bent out of round same thing . Adjustments won't typically fix those issues.
Better info may yield better soulution.
What brand chassis , mount , drivers , gears and gear hub?
 
flattop1 said:
RLV chain is adequate.
Clutch driver can be bad.
New chassis , ok . What brand motor mount?
Hub getting knocked out of round or wobbling , then an readjustment fixs it ? That sure don't seem right. Bent is bent out of round same thing . Adjustments won't typically fix those issues.
Better info may yield better soulution.
What brand chassis , mount , drivers , gears and gear hub?
Click to expand...

Let me gather all that and get back to you...
 
Quality chassis and mount .
Small drivers are the worse for this .
Maybe the problem is not really a problem .
 
our chain guard wobbled, but the gears ran true.

we must be lucky, we never had a chain come off
 
Take chain that's been run, and measure distance between 20 pins.... then some other place on chain, 20 pins. If different, that will show that your chain has been unevenly stretched, which could cause the problem. On a stocker, I could only see this being a problem with tightness or extreme flex issues... I'm used to leaving about 1" up and down play in my chains, at rest, cold, otherwise ready to run. The longer the chain the more slack you may have to run, based on theoretical chassis flex....but it's hard to see needing much more than an inch without running into thrown chain issues...
 
I had a bunch of similar chain issues a while back, it turned out to be a motor mount problem. the mount itself didn't seat accurately and the thing would virtually teeter totter on the frame where it is supposed to sit. New mount fixed it.
 
Sounds like a split sprocket issue to me.

If split sprocket:
1- Install both halves of the sprocket on the hub and tighten all 6 bolts to just before they start to grab
2- Install chain, adjust to the desired tension and tighten the motor mount.
3 - Tighten all 6 sprocket bolts starting with the center bolts in each halve. Spin axle so one of the center bolts is furthest away from the crank and tighten, do the same with the other center bolt and then tighten the remain 4
 
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