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UPDATED Transmission crunchiness, transmits nothing! :-(

Discussion in 'Technical and Troubleshooting Torque' started by mattb, Mar 29, 2009.

  1. Hey All.

    QuarterWit and I were riding along today from Melbourne, the SR500 humming all the way, and just short of Bendigo I started to lose power in a rough kind of way. I dropped it down a gear and same problem. Pulled over, had trouble getting the gear to engage from neutral into first, and then wouldn't pull. Engine off, I put the bike on the centre stand and into first gear, and was able to spin the rear wheel with my hand! At the time I assumed the countershaft sprocket had come loose, but I had no allan key to check (funnily though, it felt fine). Home six hours later after being towed, sprocket cover off and nothing looks out of the ordinary. I haven't tried to start it, but can still spin the wheel when in gear and she sounds scrunchy when I wheel the bike.

    When I turn the wheel there's a grinding sound, sort of like a bearing that's stuffed, really stuffed. Now I know what the sound is that's been bugging me of late - it's been there a long time, spaoradically, and lately has been getting worse and more common, especially (as far as I can hear while riding - with a pudding basin helmet) when engine braking. Like something metal grinding gently as it were, scraping, against something else metal. I haven't been able to locate it till now. Of the late there has been a clicking sound develop at the main axle of the drive when I wheel the bike, I had put it down to chain noise though that didn't seem satisfactory to explain it.

    Any ideas? I've never had an engine apart but I guess this is the time to learn!

  2. I would say you've done the gear or chain that drives the clutch basket/primary gears off the crankshaft. Or something is wrong with clutch basket or transmission shaft it drives.

    Regards, Andrew.
  3. I'd try pulling the clutch cover (after draining the oil) as if its a clutch problem you won't have to pull the motor outof the frame. Clutches are pretty easy to fix, so fingers crossed! If its not clutch/primary drive, its gearbox, which will mean engine out and splitting the cases. Have the credit card handy.
  4. With any luck you've just stripped teeth off the clutch friction plates. A little worse the clutch basket itself.

    After that I'd guess the spline on the sprocket or sprocket shaft.
  5. So QuarterWit and I finally took a look at the bike last night. I had looked at the sprocket Sunday night (in the dark) and all seemed fine, so we began by pulling off the clutch cover and inspecting the clutch. Everything was perfect to our eyes. So we had another look at the sprocket, and this time noticed that, while the teeth looked fine on the shaft, the sprocket teeth were stripped. In jubilation we loosened the chain to remove the $20 part, and when we did...we saw this

    The teeth on the drive shaft were stripped.

    I've contacted some wreckers and have found used drive axles for around $100 (new is $200), plus I'd need a gasket kit ($100). This would work assuming that nothing's wrong with the gears (can get both shafts and all gears for $200). There's no chance of paying someone to do it so I'd have to do it myself (or do most and get a car machanic I know to do the skilled bits for me). Another option is to buy another motor. Went out to a local wreckers with a bunch of motors but they're sharks, quoting different prices to different people (for the same motor they emailed me today at $750, then when I went out there and didn't identify myself, $1200!), and the only affordable option, one in unknown condition with the cases and electrics missing, they haven't had running - so it's a fair gamble. I could let the bike sit and wait for a good XT500 motor for $500 on eBay in the next six months.

    Another option is to take any of these options, but take the financial stress off till later in the year when I will have both more money and time (in the middle of a thesis at the moment) by:
    Welding the sprocket onto this shaft. New sprockets and chain, will get me through for a good while, then when it's time to rebuild this engine just grind the sprocket off as the axle is a throw-away item anyway. There's some teeth left and I had thought about joining two sprockets together, with the out one's teeth ground away and it sitting on the god spline...but the good bit left is only half or two thirds the width of the sprocket, so surely it is ready to strip too.

    Any opinions on the welding option? I know it's dodgy, but the shaft is a throw away, and this would get me through in the short-term for not too much money...

  6. I'd do both; weld two sprockets together, then weld the sprocket to the shaft. If you weld the outside of the outside sprocket, (if that makes sense) to the shaft, you should also avoid having heat transferred along the shaft into the 'box (although perhaps you should change the oil after this exercise anyway?)

    I assume there's enough room under the case to accommodate two sprockets together, btw???
  7. It'd want to be a bloody strong weld. Heat transfer issues aside, I don't know how secure I'd feel that I wouldn't be in for another trailer ride.
  8. I've seen sprockets welded to output shafts. It worked, but a few questions always nagged at me. The chief one being whether you can still get it all apart when the time comes to rebuild. A supplementary one is that, although I wouldn't expect sufficient heat transfer to bugger bearings or gears, there might well be enough to do your output shaft seal a power of no good. Which you can't change, because you've just welded your sprocket on.

    Personally, I'd do the welding two sprockets together trick. Tack 'em on the bike so they line up correctly, then take them off so you can really give the welder a bit of welly without worrying about what's happening to other components. If it subsequently fails, you can always go the whole hog then.

    As a budget engineering alternative, and if you're resigned to welding on the shaft anyway, dismantle it all, build up the buggered splines with weld and file them back to shape. It's hard work and time consuming but needn't cost anything but beer for whoever does the welding and the price of a file or two. In theory the splines should be machined back to shape and the shaft heat treated, but the splines in the average aftermarket sprocket generally aren't too flash anyway (so high precision is a bit of a waste) and I'd just chance the heat treat, letting the welded shaft cool naturally, away from draughts.
  9. Thanks guys.

    I'll have to chew on this one, but I think I'll go the weld. You're right Loz, but that's what RACV Total Care is for. I will speak to that car mechanic tomorrow.

    Somebody suggested this to me: "If the thread is OK ,lock on a good sprocket & weld up the sprocket to the nut & then weld the nut to the shaft .Probably better than new but you'll have to do something before the next sprocket change ! You'd have to be careful of the heat travelling up the shaft into the bearing ,so you may have to do it in spurts cooling it as you go."

    Rather than the two sprocket option - I don't trust that remaining spline - I might actually grind (file) down the remaining spline so that I can follow this suggestion by fitting the socket into place with the bolt, tacking it with a couple of welds, and then removing it (winding it off - hence the grinding of the spline) so as to weld it to the bolt off the shaft, thus minimising heat on the shaft, and only the bolt needs to be welded on the shaft. You know, if it came to it I could actually do this a few times, just grind off the weld/end of the shaft and get a new nut with each new sprocket! I'd also do two chains to a socket set, which is a moot point but a lot of people reckon they're good for that (of course what matters is what is shown in inspection each time). Though presumably I'll work on the engine before the chain is used up.

    When time comes to open up the engine, I'll just grind down the end of the axle!


    Ps the axle has about 4mm play in and out, is that normal?
  10. Can you fit a chain on two sprockets that are stuck together? I'd have thought they'd be too close for the chain to seat properly.
  11. Just need to grind one down - all the teeth off obviously, but smaller than that slightly - small enough that it and the chain on the other sprocket clear one another.

    Another option http://cgi.ebay.co.uk/XT500-TT500-SR500-FRONT-SPROCKET-15-16-17-TEETH_W0QQitemZ120357051486QQcmdZViewItemQQptZUK_Motorcycle_Parts?hash=item120357051486&_trksid=p3286.c0.m14&_trkparms=72%3A1777|66%3A2|65%3A12|39%3A1|240%3A1318
    Though that might be harder to weld the nut to, if I decide to do so and which is striking me as the best option because it involves heaps more surface welded, and of course the nut is not only welded to the shaft but also bolted! I'll have to check out the outer diameter of that boss, the nut has a cavity on the inner side which might clear that sprocket's boss and so I could still wled as I intend to, making for "Wah ha ha ha!" time.