Sprocket issues re-visit...

pjmcburney · Post by **pjmcburney** » Sun Mar 22, 2009 6:13 pm

Hi all,

Can someone give me some advice about wear on the countershaft from sprocket movement?
I too run an o-ring chain, and I use the 'couple of lock washers' arrangement behind my countershaft sprocket to provide clearance for the chain.

Now...
My sprocket keeps coming loose.

Every 1000 or so kms I have to flatten the lock washer, lock the transmission, heave on the sprocket nut then refurbish the whole shebang only to have to repeat the procedure in another 1000 kms.

I did it again on the weekend only to find that there is now appreciable wear on the countershaft from the sprocket moving back and forth - so much so that there is approx half of the spline worn away where the sprocket sits. The sprocket is obviously much harder metal than the countershaft so it's going to wear first - who's idea was that?

I have a half-dozen countershafts in the shed, all with varying degrees of wear - some are pretty good, and are candidates for a replacement.

But... to replace a countershaft is a BIG job, so how long can I keep re-tightening the sprocket nut and/or is there some way to prevent it from moving on the worn shaft apart from doing it up really tight?

Thanks
Paul

tz375 · Post by **tz375** » Sun Mar 22, 2009 6:27 pm

Paul,

That sounds like the sprocket is moving on the shaft even if it's tight. So as you get on and off the throttle it's chafing away and loosening the lock washer.

Gordon (ILbikes) posted a picture of his output shaft and it had a very short oart of full splines and then the splines tapered out. If yours is similar, you need to machine the rear sprocket carrier instead to move the chain and sprocket inwards slightly.

You may have to look through your countershafts and see if one of them has more spline depth that the others.

teazer

ilbikes · Post by **ilbikes** » Sun Mar 22, 2009 8:04 pm

Paul, I did some measuring as Richard said and I deided against the washers on the backside. The splines are not deep enough -

Here is a link to the research and conclusions -

Regards,
gordon

http://www.motorcycleracer.net/phpBB2/v ... .php?t=894

pjmcburney · Post by **pjmcburney** » Sun Mar 22, 2009 8:25 pm

ilbikes wrote:Paul, I did some measuring as Richard said and I deided against the washers on the backside. The splines are not deep enough -

Here is a link to the research and conclusions -

Regards,
gordon

http://www.motorcycleracer.net/phpBB2/v ... .php?t=894

Thanks for the replies...

I've read through that thread (very comprehensive!) and the only logical solution, really, is the H2 sprocket setup.

I'll do some digging and see if I can get my hands on one locally.

What I was hoping was someone who was having a similar experience and what their (temporary) solution might be.

I'll keep y'all posted
Cheers
Paul

pjmcburney · Post by **pjmcburney** » Sun Mar 22, 2009 10:46 pm

Quote from Gordon:

Now, I will be turning the wheel/drive on the stand to carefully and thoroughly confirm, but for now I'm thinking I'm ok. I purchased a used drive hub and sprocket assembly on eBay last week just for the purpose of having a machinist friend make me a spacer/shim to match the hub's pattern. If fit between the rear hub and sprocket and made from stainless sheet, I could use blue Locktite on both sides of the shim and not lose the hub/sprocket clamping. This would keep the load off of the 6 sprocket bolts which aren't really supposed to take the full shock/load and are for clamping. I'll add this shim only if absolutely necessary and have yet to bend my locking tab washers over my sprocket nuts for this very reason.

Hmmm...

I decided to assemble the sprocket back onto the hub using six suitably sized washers between the sprocket and the hub to space it out slightly, as on my bike the chain does leave the front sprocket on a bit of an angle.
I was careful to torque all six bolts/nuts down the same (at 40Nm).

Am I now at risk of shearing the bolts because there is no complete clamping pressure between the sprocket and the hub?

Those six bolts are high-tensile 10mm jobbies - surely it isn't possible to shear them with the modest power output of a GT?

Ya got me worried now...
Paul

ilbikes · Post by **ilbikes** » Mon Mar 23, 2009 10:06 am

Paul, I don't want to have the hub and sprocket seperated and if it becomes necessary, I will use a full size shim with threadlock on both surfaces. No, those bolts aren't designed for side shear - their design was for 80% clamping - 15~20% side load. Of course, these are my estimates.

Now for real-life experience. My 1967 Honda CB450 Black Bomber uses studs that bolt onto the rear sprocket. These studs are actually tight-fitting pins of about the same 10 mm diameter and 35mm long. those were designed to live happliy threaded tightly on the sprocket and inserted into their tight-fitting hub holes. Even with the lighter 350 lbs of bike, all 43 optimistic horsepower, with no torque - these almost always ruin the sprockets in short time, the holes in the hub are wallowed-out, and the threads on those hardened stud/pins can and do shear off. The sprocket and it's pins are held into the hub with a huge C-Clip and large washer (about 3" in diameter).

The "missing link" on these in my opinion was of course the "clamping of the sprocket's surface to the hub". Left entirely on their own, no I do not believe they are made for the load. Add all of the extra weight and contrary to belief, the 2 stroke makes more torque than any 4 stroke of comparable size - your spacers will lead to premature failure. Making a full-size shim and re-gaining that surface patch would be a priority to me.

But as Lane and others have said, sometimes I make-up stuff to find solutions to.

Regards,
Gordon

ilbikes · Post by **ilbikes** » Mon Mar 23, 2009 11:08 am

I went and found a drawing of the rear hardened pins system used on the 450 Honda. Those are hardened steel inserts that fit into the hub with a thin rubber cushion. This is why I have concluded that the side loads on the bolts would be a bad idea -

Gordon

tz375 · Post by **tz375** » Mon Mar 23, 2009 2:27 pm

Well, that 43 Hp honds isn't the only one destroying hubs and sprockets.

We had a situation at Mid Ohio with a CB160. So OK it has a 175cc motor with 1mm oversized pistons for a mind numbing 21HP, but it also wore out the sprocket and the hub and two of the studs had sheared off.

It's not a smart design, but it's not teh lack of clamping force that destroys them. It's the fact that they are loose and can move around. Those studs are always in tension but the mode of a failure is the shearing force. Whether or not the bolts are tight makes little difference to that shear force, but the looseness makes a huge difference.

Using a spacer increases the likelihood of failure through repeated bending and most importantly because it rocks back and forth.

After Gordon's thread I checked a couple of output shafts and they have some serious wear and very little support. I want to try an offset sprocket and get rid of the spacer behind the sprocket, for a deeper spline engagement.

pjmcburney · Post by **pjmcburney** » Mon Mar 23, 2009 4:18 pm

tz375 wrote:After Gordon's thread I checked a couple of output shafts and they have some serious wear and very little support. I want to try an offset sprocket and get rid of the spacer behind the sprocket, for a deeper spline engagement.

I rummaged around and found two of my spare output shafts yesterday.

I did some rough measuring and discovered that the fault lies with the design of the shaft itself. Suzuki dropped the ball on this one.

The full depth width of splines on the end of the shaft on either of the ones I have is 6mm at best (more like 5.5mm on average), from the end of the spline taper (there is a machined 'edge' at this point) to the beginning of the the threaded section wherein the spline depth decreases significantly (approx half) due to the cut-in of the thread.

Now... the sprocket itself is 9mm wide. This means that even if you can run the sprocket at maximum depth on the shaft (i.e. with the sprocket hard against the machined edge of the spline taper where it can't move 'on' any further) you still have 3mm (or more) of the sprocket riding against the threaded portion of the splines.

The practicalities of the arrangement mean that even if you don't run spacing washers or you run a H2 sprocket with the step on the inside you'll never get full width contact with the full depth splines.
You can't for two reasons - a. the sprocket is wider than the splines (duh), and (even worse) b. the machined edge is hidden by the seal spacer preventing the sprocket from seating fully on the shaft.

The only complete solution (IMHO) is to remanufacture drive shafts with longer/deeper splined sections.

I'm not sure why Suzuki didn't do this right from the get-go. There's plenty of room behind the cover to accommodate a longer shaft.

Gordon,

For the time being I'm going to take my chances with my spaced sprocket setup.

I'll keep a very watchful eye on it...

Cheers
Paul

ilbikes · Post by **ilbikes** » Mon Mar 23, 2009 4:23 pm

I want this - does anyone have one, has anyone used one before?

I realize that you will have to remove the chainguard, but to set-up perfect reference alignment every time, it seems a perfect tool to have.

Anyone want to talk me out of one?

Gordon

tz375 · Post by **tz375** » Mon Mar 23, 2009 4:52 pm

Gordon,
I have one and it's a useful tool.

Paul,

Thanks for that analysis. It matches what Gordon found. I think I'll just get a dished sprocket made up and go without the spacer. That way I'll get all the spline engagement needed in the "offset" part of the new sprocket

ilbikes · Post by **ilbikes** » Mon Mar 23, 2009 6:16 pm

Guys, if you can't get the sprockets, let me know and I'll have Laurie send me a couple. Kawasaki has discontinued them and you really want the hardened ones like she carries. All sprockets are not created equal - I had to get that little bit taken off using a flywheel surfacing machine. - Some tuff stuff and should easily hold up to 20,000 miles the chain will.

My cost was about $23 each including shipping.

Regards, Gordon

tz375 · Post by **tz375** » Mon Mar 23, 2009 10:04 pm

Gordon, are they available in a 520 thickness (thinness?)?

I'd prefer to go down to a 520 high performance chain and narrower sprockets and it would allow the sprocket to be thinned from the back and that would gain a little more spline engagement.

Suzukidave · Post by **Suzukidave** » Tue Mar 24, 2009 4:34 am

It looks like Suzuki noticed the short comings of the output shaft design as beginning with the GS series they switched to a multi point shaft that they still use to this day on the GSXR's .. so they did know they had a problem but never fixed it . Now if there just was a way to put a GS750 output shaft in the GT cases ?

Suzukidave · Post by **Suzukidave** » Tue Mar 24, 2009 5:01 am

tz375 wrote:Gordon, are they available in a 520 thickness (thinness?)?

I'd prefer to go down to a 520 high performance chain and narrower sprockets and it would allow the sprocket to be thinned from the back and that would gain a little more spline engagement.

Richard ,i am going to be useing a 520 chain on the new build .