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Rear axle help, drum won't rotate, chain slap also

Discussion in 'The Garage' started by kawabunga, Jul 27, 2020.

  1. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    The backer / spacer on the brake shaft can be installed backwards, it will make the wheel bind because will push the shoes against the side of the drum
    GLJ likes this.
  2. kawabunga

    kawabunga XS650 Addict

    I already have one on the bottom, it’s not cutting it though. I’ve heard of people using two. Might try that.

    Boog likes this.
  3. Jim

    Jim Beyond the edge, is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Might wanna consider taking the existing tensioner off and see what happens. Could be the tension from that along with the new pivot position is setting up a resonate vibration in the chain. Couldn't hurt to try it...
    lakeview, kawabunga and gggGary like this.
  4. kawabunga

    kawabunga XS650 Addict

    5t, you are correct, my terminology is incorrect. My apologies for confusing everyone... When I mentioned the “drum” I was referring to the brake shoe plate/backing plate/brake plate. My bad. I had the terminology mixed up.

    My drum, or hub, spins just fine when everything is installed. Never had any issues there.

    My brake plate does not rotate when the axle is tightened. Which, according to everyone, should not rotate when the axle is tightened anyway. So that’s good news! I thought it was supposed to. Also, for reference, I took the brake stay arm off of my CB550, the drum does not rotate freely on that bike, like I thought it did. I think it may have spun once when I hit the brake without the stay in place on the lift. It moves a little when I spin the wheel and hit the brake but I can’t move it easily hand. I’m not entirely sure where I got the idea. Either way, thank you all for setting me straight on that!!

    Now I can move on from that knowing it’s not a dilemma, and sort out my spacing issue so I can properly torque the axle down. After more research and discussion with an ex-motorcycle engineer, I’m thinking the axle/brake have nothing to do with my chain slapping around, but is more of a result of my suspension design, longer chain, and the engine characteristics. So that will still need to be dealt with. Got ideas? I’d love to hear them. I have a few experiments that I will be performing, and report back the results, once the bike is back together.
    Boog likes this.
  5. kawabunga

    kawabunga XS650 Addict

    Im going to add that to my list of experiments :)
    Jim likes this.
  6. kawabunga

    kawabunga XS650 Addict

    Gary, which part are you referring to exactly? I’m not confident I know which one you’re talking about.
  7. kawabunga

    kawabunga XS650 Addict

    Thank you for measuring those!
    I also measured the overall length and found it to be roughly 32mm as well.

    Would you mind doing a quick measure of the rest of the spacers?

    Here’s what I found:
    The left side spacer with the dust cover - 31.1mm
    Top hat spacer - 20.9mm
    Spacer between bearings - 84mm
    The right hand spacer outside the brake plate - 25mm
    Boog likes this.
  8. Machine

    Machine Race the wind Top Contributor

    Kawabunga, do you by chance have one of these 78 era brake cam spacers?
    This era / style spacer has to be oriented correctly or one lobe will interfere with the drum casting.

    Attached Files:

  9. kawabunga

    kawabunga XS650 Addict

    Machine, I believe the brake components are from ‘79, but I can’t be sure. Will have to check.
  10. stinky78

    stinky78 XS650 Enthusiast

    I think the main problem with the suspension design is having the pivot point below the bottom run of the chain rather than between top and bottom like normal, that and the distance of the swing arm pivot from the front sprocket, the normal set up doesn’t give as much leverage to try to shorten the chain, though you do get squat under acceleration, it’s not as exaggerated as in this set up, now it’s built it’s a bit hard to do anything about the design, just need to find ways to work around it’s short comings, when I first looked I didn’t see the tensioner, do you find you get a lot of squat/compression of suspension under acceleration?
  11. DaveO

    DaveO XS650 Addict

    I'm sure if I could find my compasses and could remember all that stuff about radians and arctans and cosines I could work it out but here goes.

    From the picture above you seem to have moved the pivot point of the new "swinging arm" considerably rearward of the pivot point of the old swinging arm. This means that the radius of the circles it describes is much smaller, and the arc of the circle it describes is tighter.


    This means that as the suspension compresses the arc of the new arrangement departs from the path of the old arrangement and moves inboard.


    Your chain slack may be coming from the bit I've marked in yellow.

    To not have any additional slack introduced as the suspension moves the pivot point would have be the same as the centre of the front sprocket. Obviously, this is difficult to engineer so normally the swing arm pivot point is just kept as close to the sprocket as possible.

    Of course, I could be wrong.
    Jim likes this.
  12. kawabunga

    kawabunga XS650 Addict

    The pivot point is between the top and bottom rung of the chain. The angle this photo is taken at is a bit deceiving.


    Some, but not much.

    Dave, you may not be 100% correct, but you're definitely not wrong. I did move the swingarm pivot rearward, and that does change the radius and how it interacts with the countershaft significantly. The height of the pivot plays a huge part in that as well. And the suspension travel direction...and the amount of suspension travel...and the shock pivot points...and the distance from the swingarm pivot to the axle...and so on. I'm not a mechanical engineer, I did my best with the knowledge I had at the time. The suspension works just fine as is but it has created the chain slack issue. Since it's all welded together now it's quite difficult to do much about the design without basically starting over completely. I understand why it's doing what it's doing, I'm looking for ways to limit its affect.
  13. DaveO

    DaveO XS650 Addict

    I'm not an engineer, and I'm not implying any criticism. :) The work is outstanding. Far beyond my abilities. Hope you get it sorted.

    kawabunga likes this.
  14. kawabunga

    kawabunga XS650 Addict

    All good, Dave. I appreciate your input. Sorry if my reply came across as snippy, I didn’t mean for it to be. If anything, I’m just more frustrated with myself for creating this problem on my own accord. If only I knew then what I know now...
    DaveO likes this.
  15. DaveO

    DaveO XS650 Addict

    You've not created a problem. Its a "development opportunity". You think the guy who thought up the points ignition was disappointed by burning points and gave up? Nope, he added a condensor to solve the problem. Bikes don't start easily with static timing. So a doo-dad was added to retard it for start up. Heck, the XS1 has a decompressor. I'd like to have been a fly on the wall at that first test start before the "fix". (BTW - The first time I ever saw the starting cable pull and heard one start on one cylinder I thought it was the coolest thing I'd ever heard. I was hooked.)

    You'll sort the problem and you'll be able to say , "The design of the suspension keeps the back end clean but of course I've had to add a chain tensioner top and bottom to take up the slack at full compression."

    How cool is that?
    GLJ, gggGary and Jim like this.
  16. stinky78

    stinky78 XS650 Enthusiast

    sorry! my mistake, I take back what I said about the pivot point, I thought the bolt below it was the pivot, was viewing on my phone while at work, like Dave I’m also not being critical, I”d be to scared to undertake a project like that myself, just trying to put ideas out there that might help, the only thing I can think of is to use a shock with adjustable compression damping, if your current one doesn’t have it that is.
  17. 5twins

    5twins XS650 Guru Top Contributor

    I don't have a wheel hub apart at the moment to check the internal spacer lengths, but I managed to find that info (or links to it) on the site here. For you, it's sorta good news, bad news. Good news - your internal spacers appear to be correct and OK. Bad news then is they aren't the source of your binding or rubbing .....



    So, it may come down to, as Machine mentioned, the assembly and installation of the brake camshaft and it's funky shaped spacer washer into the brake plate. '74-'79 brake plate castings had a boss below the camshaft hole for an electric brake wear switch. Even though the switch was discontinued about mid '77, the casting remained .....


    On the funky spacer washer used, the top side was cut out for the camshaft to fit down into and the bottom side was dished out on one side to clear the plate casting .....



    That dished out section must face down towards the bottom of the brake plate. One more little thing on the install. This doesn't have anything to do with rubbing but rather best braking operation. The camshaft is not symmetrical, one side of the cam portion extends off center slightly more than the other. This moves one shoe slightly more than the other to compensate for the difference in distance between the shoe pivot point and the contact point of the cam to the shoe. The difference is so small, you can't see it with the naked eye so Yamaha marked the outside end of the shaft with a dot. This dot should be faced in, towards the axle .....

    gggGary and Machine like this.

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