[Norm]

How does this sound for an idea? We all spend time trying to get the front & rear sprockets perfectly aligned. If you remove the locking ring off the front one & just put a safety collar on the end of the shaft, your front sprocket will be free to align itself by floating back & forth on the output shaft. Good idea or dumb one?

 

[22690]

That's how my husqaverna chain saw works.

 

[Speeddog]

As long as the sprocket can't go inboard far enough to start 'milling' the case, it'd probably be alright.

Are you intending to use a snapring in the groove on the countershaft?

 

[DrunkenMonkey]

My question is what are the forces acting on the front sprocket now that it's floating?

Basically, will it have a tendency to align itsself or not?

If the forces are neutral it'll just wander back and forth and never be aligned.
If the forces are 'unstable' bad things will happen and finally if the forces promote stability, it'll work.

What I suspect is that as long as there's tension on the chain, the floating sprocket will be pulled to the closest point to the source of the tension (i.e. the rear sprocket) so that makes me think it'll be self aligning.

However, if the tension on the chain goes away, or worse there's somehow a 'pushing' force from the chain (slack chain + chain's momentum) it'll want to push itsself out of alignment.

Seems to me under normal use (mostly under tension) it'll be mostly in alignment.

However, I suspect that when it's under tension the stiction of the sprocket to the shaft will make it not want to align/move, but when it's not under tension (and it's in an 'unstable' state) that stiction will go away and it'll be free to move.
So basically it'll be more free to move when it's in an unstable state then when it's in a alignment promoting state...

But what do I know? I only play a physicist on the Internet ;D

 

[MotoCreations]

Theoretically it would work ala Norms comments. My concern would be the parallelness between the sprocket and rear axle itself. If the rear axle wasn't aligned properly it could (and should) move the front sprocket inward/outward to compensate depending upon the lateral stiffness of the chain and the torque factor. I've seen way too many bikes with the rear axle not properly aligned (or swingarm bent) with the front sprocket. I vote to retain the locking ring as there isn't much to gain by leaving it off. If weight is a concern -- just drill the front sprocket itself.

 

[Norm]

Good point about the potential angle problem. I'm trying it now on a bike & just bolt a small plate to the end of the output shaft with an 8mm bolt (the threaded hole is already there). On the inside, the splines don't extend far enough for the sprocket or chain to rub the cases, but since they end in a taper, it might be able to jam itself in there. (?)
I'm also wondering what the forces will do when downshifting.
I've got a couple hundred miles on the bike, without noticing the sprocket moving from it's self-aligned position, but I can't watch it while it's running, only at rest. I'm thinking I might wrap some tape on either side of it to measure any movement.
If you never hear from me again, that means it didn't work.

 

[JJGeo]

I'm also wondering what the forces will do when downshifting.

I'd think the forces when downshifting are very similar to those when accelerating, only it is the bottom of the chain in tension instead of the top. Either way the force will act to try and center the sprocket.

 

[mandrbarrett]

I think the discussion here has completely missed one point which is far bigger than the alignment of the chain and sprockets.

What you are really doing when you position the rear wheel after adjusting the chain is aligning the wheels.

If the wheels are out of alignment then the bike will handle like a bag of shite, and you won't need to worry about sprocket wear because you won't want to ride it far enough to wear the sprockets out.

If you get the rear wheel aligned then the sprockets will automatically be in aligment, because the bike was built that way, so you don't then need to worry about sprocket alignment.

If you are really referring to sprocket offset, ie the distance between each sprocket and the centreline of the bike, then yes that is very important and if it is unequal then you will wear out a chain in no time flat, but how on earth can that ever be wrong, given that it was correct when the bike was built adn you have no adjustment for it?

Basically if the bike is well maintained and the sprockets line up as they did when the bike left the factory, then adding some float will only let the sprockets move out of alignment, so whether they float towards the optimum position or away from it is pretty irrelevant.

Mark.

 

[Norm]

The reason I'm experimenting is because when the wheels are perfectly aligned, the sprockets are frequently misaligned (yes, even on a brand new bike). When I set up a bike, I always align both wheels first & then have been shimming the front sprocket to match. Most people just line up the sprockets & don't bother with the wheels, assuming they are correct. The floating sprocket idea just seems logical to me but I've never heard of anyone doing it before & that always makes me nervous.

 

[mitt]

I think there is a problem with this, I will draw it up to explain, but it deals with clearances between the chain links and the teeth, the chain will "never" be centered on the sproket, thus always pulling inward or outward.

And, since there must be a little clearance for the sprocket to go on the output shaft, the force would tilt the sproket one way or the other, causing a walking affect along the shaft.

drawings to come...

mitt

 

[mitt]

Quick sketch showing output shaft, sprocket, and chain links, top view cut away:

 

[toolfan]

My DR650 front sprocket is just held on by a circlip on one side, and there is generous movement allowed - haven't seen a problem with it, and I've never heard of DR650s smoking output shafts or sprockets unreasonably fast.

 

[mitt]

My DR650 front sprocket is just held on by a circlip on one side, and there is generous movement allowed - haven't seen a problem with it, and I've never heard of DR650s smoking output shafts or sprockets unreasonably fast.

The movement that happens on the DR must not be enough to cause any problems, so my theory must be just accademic, not practical.

mitt

 

[Norm]

Part of the benefit of the floating system is that the sprocket slop (for lack of a better term) would always zero out as the chain kept it straight. The chain will align with the fixed rear sprocket & force the front sprocket to the correct spot on the output shaft.

 

[toolfan]

The movement that happens on the DR must not be enough to cause any problems, so my theory must be just accademic, not practical.

mitt

Actually, I'm not even sure what problems your theory highlights. If you think about it, the distances you are talking about are very small, small enough that a retainer or a nut would probably allow the same rocking motion, just without the walking. The gap between the shaft and the sprocket has to be a few thousandths or so, so, the movement to take up that slack at the top of the sprocket would be on the order of 1/3 of that, so, maybe .001"...

 

[greenmonster]

On my -97 the sprocket can move a mm or 2, isn`t Ducati already doin
what you thinkin, Norm? But maybe in a smaller way?

If you never hear from me again, that means it didn't work.

That`s the spirit! ;D

 

[mitt]

Actually, I'm not even sure what problems your theory highlights. If you think about it, the distances you are talking about are very small, small enough that a retainer or a nut would probably allow the same rocking motion, just without the walking. The gap between the shaft and the sprocket has to be a few thousandths or so, so, the movement to take up that slack at the top of the sprocket would be on the order of 1/3 of that, so, maybe .001"...

I thought that is the sprocket was always walking one way or the other on the output shaft, that it could lead to faster chain sprocket wear, since the teeth might not be touching the chain on a line contact, but more of a point contact.

mitt

 

[bozcorob]

All we need is someone with a super high speed camera set-up and we will be able to see the effects of
the front sprocket float or lack thereof...

Anybody have access to one? (Or a spare $25K to get one)

 

[Norm]

I have zip ties & electrical tape - that ought to do it.

 

[jerryz]

My 2001 S4 appears to have a floating front sprocket a standard, its in good condition but has a perceptable amount of movement when i examine it closely.

jerry