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Chain slack 70mm GPX250

Discussion in 'Technical and Troubleshooting Torque' started by TCShadow, May 20, 2009.

  1. On a GPX 250 I've been riding for about 4700km... Had a 1000k service before I bought it. Should I have 70+mm chain slack? Most of the slack is up... I pull it down maybe 10mm but up it moves heaps.

    I'm about to take it in for a major but I'm curious if the chain should be this far off spec. Never thought to check it before yesterday. Spec is 30-40mm.
  2. :shock:
    You really need to tighten that chain before it comes off.

    It sounds like its either hasn't been cleaned and lubed properly or that it's really old.

    I would tighten it before the service is due, it's easy to do.
  3. The slack is the same dimension up and down. You are measuring from where it is hanging at the moment. If you can move it down 10mm and up 70mm then you have 80mm of movement so ±40mm. Probably still too much, but remember that the only thing worse than a chain too loose is a chain too tight. As your swing arm moves up, the chain will tighten, so if too tight, a serious problem. Chain spec for each bike is a bit different, so check your manual or see if you have a sticker on your swingarm telling you the required slack.
  4. probably only want around 30-40mm of slack, suggest you tighten it. as said, slack is measured as the distance between the lowest point when pulled down, to the highest point of of the same link when pulled up. dont forget if you start your measurement from the bottom of the chain, to measure to the bottom of the chain not the top. confusing these two can add or subtract 10mm from the correct value, coz you're adding or subtracting the height of the chain.

    is it lubed correctly? not rust or very dry?
  5. It's lubed correctly... I haven't cleaned it much though... generally just a wipedown and lube. I've booked it in for the service tonight so I'll see what it's like when it comes back. I also didn't bother to find the tight spot before measuring so it's probably not quite as bad as 70mm...

    And it was 70mm all up not 10 down and 70 up.

    I'll specifically mention it to the workshop when I drop it in even though it's something they should check and adjust if necessary.
  6. 70mm definitely too much - from memory GPX is somewhere around 30mm as per service manual - also check if it says measured on sidestand or centre stand, as that can make quite a difference.

    If there's a tight spot of any more than about 10-15mm difference your chain is buggered.

    Maybe don't mention it to the workshop, then you'll get an idea of how much attention they actually paid to it! :wink:
  7. you should be re-adjusting the chain every week or two, just give it a bit of a nudge with your foot every time you get on the bike, and if it looks like its out, adjust it. If you let it get too loose, it wears itself out faster, so it gets even looser. It sounds like this is what happened, you didnt make any mention of adjusting the chain yourself.
  8. DIY if you've got the tools and know how.

    It's pretty easy since the GPX has a center stand.

    Here's the GPX knowledge base:

    Generally, when chains become slack, the throttle action is "laggy" on shifts as the power has to take up the excessive slack in the chain.
    If there are significant tight spots, I find that on constant throttle, the bike can become jerky as the chain tightens and loosens .

    I clean/adjust my chain (if required) every 500-600km.
    Clean, freely moving links in the chain makes the ride much better. :grin:
  9. Thread resurrection!

    I usually check the lube the chain every 400 - 600km. I guess I got lazy and put on 800 - 1000km before checking it just now. It's loose as! I can push it up and it'll touch the swing arm :shock: . Didn't know it could get so loose so quickly but then I guess I do a lot of km in a week. Plenty of adjustment left but I'll keep a closer eye on it from now on.

    Oh, yeah, I definitely know what a loose chain sounds like now :p
  10. Lesson learned, I hope.

  11. so its 40mm chain slack?..... always confused me that chain can travel up higher than lower
  12. So far two separate definitions seem to have been given regarding what the actual value is for the chain slack. The first is 0.5 x (the distance down + the distance up) and the other is (the distance down + the distance up). For the two times I got my Ls at HART, they said distance down or up as the slack.

    The first definition makes the most sense to me. The second way has me thinking that the chain would be pretty tight if 20-30mm was the free play that way. For the record, it is <10mm down and about 30mm up on my bike and that seems ok to me. The spec is 20-30mm for the slack so its either at the bottom or top end of that tolerance. Which one is it?
  13. slack = the overall amount up and down.. most owners handbooks have a little picture to explain this.
    70mm on a 5000km chain.. faaaark. shoot the mechanic please.
  14. eg. so i measure the bottom of the chain, it goes down 10mm. measure it up 20mm. so all in all i have 30mm chain slack.? dont have a owners manual. have a service manual, but doesnt say much about slack, tells me how to change the chain though
  15. That' right.

    Pretty simple - if the chain's slack it 'hangs' below horizontal (neutral, or shortest - straight line - path between the sprockets) because it has gravity pulling it down. If you hung the bike upside down it would 'hang' the same distance in the opposite direction - towards the swingarm. When you push a loose chain up it goes through that horizontal line to what should theoretically be the same distance above horizontal.
  16. well duh *slaps head* .... now why didnt i think of that
    cheers horse
  17. as far as ive seen the slack for a cbr250 is 30 - 35mm. stick it on a rear stand and put in first gear. get ya mum or dog to push down on the back of the wheel. now when you push the chain up and down half way between each cog and measure from the top of the chain to the top of the chain. as in
    push up - mark location
    push down - mark location
    that distance is the slack.
    adjust to suit.
    check it the next day.
  18. push down on wheel? or the seat
  19. the wheel dude. as in spin it backwards to get tension on the top of the chain as you measure slack on the bottom. if you have measured the slack with no tension then it will be higher.