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I have a Yamaha XJ600 diversion with a sidecar fitted.

Recently had to fit two new tyres and a new rear sprocket for MOT.

Chain seemed fine afterwards for a while but all of a sudden started making a terrible noise. When I stopped and inspected it seemed the chain was really loose.

If the bike is pushed forward in gear(even with clutch pulled in) the chain is tight, but when rolled backwards it is really loose. It's also loose when rolled back or forward in neutral.

Thought about just tightening the chain but I'm worried that if I do then it will be too tight when on the go and could snap or cause damage.

Could it be the wheel alignment? Is the chain just loose and tightening up when tension is put on through pushing forward? Might the front sprocket be damaged? Or something completely different?

With the sidecar fitted it's awkward to get in to work on the bike (to check front sprocket etc) so thought I would ask and see if anyone knew what might be the problem first.

Thanks, Steven

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  • Did you replace the sprocket and retain the old chain?
    – DucatiKiller
    Mar 14, 2016 at 15:51
  • Did you check the tension with the suspension loaded? Chains always seem loose when nobody's sitting on the bike. Also make sure the axle is perpendicular to the centerline of the bike, if the nut wasn't tightened properly when the wheel was off it could have canted a bit in the swing arm.
    – TMN
    Mar 14, 2016 at 15:59
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    It sounds like your assessment of "tight" and "loose" is based solely on the droop of the lower span of chain from the bottom of the rear sprocket to the transmission output. If so, the tightness isn't changing. You're just seeing tension or slack in that section based on movement direction. (I can't think of any other reason it would change rolling forward and backward, unless the suspension is also going up and down.)
    – Tim B
    Mar 14, 2016 at 17:30
  • Steven....if you register yourself as a user you can access the site from multiple web browsers. Currently, you are marked as unregistered which means you only access the site with a cookie in the browser you posted your question from. Just an FYI.
    – DucatiKiller
    Mar 14, 2016 at 19:34
  • @TimB is correct pushing the bike makes the rear sprocket drive the front, so which run (top or bottom) of the chain is tight and which is loose in entirely dependent on whether you push the bike forward or backward. The total chain slack is best measured with the rear wheel off of the ground and the gear in neutral. - but beware that this will be the tension with the suspension unloaded. for the tension that would be on the chain in use. sit on the bike and push it backwards, then with someone similar to riders weight still sat on it: check the tension.
    – charmer
    Jul 4, 2019 at 11:21

1 Answer 1

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High Spot

If I were to guess, you have a 'high spot' in your chain.

Cause

High spots have occur for a number of a reasons

  • Ongoing poor care

  • Low quality chain

  • 'Clutch Dumping' which causes stretching of the chain.

  • Water penetration of a few rollers leading to rust and inconsistent where on those rollers

Remedy

For now, adjust your chain to the highest point of tension. Roll the bike forward or backward in neutral and find where the chain is tightest. Adjust the rear wheel distance at that point.

Long term you will want to always change both of your sprockets and your chain at the same time. Why, you ask? Because they wear together as a team, so to speak. The surfaces of the rollers in the chain and distance of the rollers within the chain change with wear over time. As your chain wears it mates into the sprocket and they all wear together.

If you only change your sprocket and retain the old chain you can get a condition where the rollers on the chain are only 'loading' the last few teeth of the sprocket before they chain and sprocket separate.

If buy a bit of a higher-end chain your chances of getting stretch and having high and low spots on your chain over time will be reduced. With the most expensive chains that I purchase for my motorcycles I have nixed this issue and it doesn't occur for me. Typically chains with o-rings between the plates will have a longer life span than non o-ring chains as they will prevent moisture and rust in the roller because they are sealed with grease.

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  • to attempted editor. I intended to use the word wear as in worn within the post. TY for looking out though.
    – DucatiKiller
    Mar 15, 2016 at 6:38

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