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Help No final drive.

Discussion in 'Hyosung 250cc' started by Rob1976, Apr 7, 2018.

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  1. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Possibly use a thread file to clean up the threads as well.. As long as you get a reasonable bite and use a lock washer it should be fine... agree with the loctite and if all else fails... weld the sucker as insurance.
    No point in spending on a gearbox rebuild unless you really have to...
    Use a new sprocket as well... normally the sprocket would be the sacrificial item.. ie softer than the output shaft which will probably be hardened.
     
    Andych, Apr 8, 2018
    #21
  2. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I did that on mine - got a few more months out of it till it tore completely through the splines - my difficulty was getting a replacement countershaft, one wrecker wanted $300 for the complete transmission...

    If you need to ride it, tack weld it as the shaft is toast for the longer term, it will work for the short term.
    You could have it turned down and a new thread cut, however that requires disassembly which means just replace it

    How long have you owned the bike?
    How many Km's on the engine?
    Is everything good and happy with the engine?
     
    ruckusman, Apr 8, 2018
    #22
  3. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Clean up the threads and the shaft as best you can with some kero / degreaser, then I would JB-weld the sprocket/shaft to make up the missing teeth. Has to cure for 24-48 hours but I think it's a better option than tack welding it.

    JB weld can be cut and machined after the fact as well, so the shaft could be salvageable.

    Obviously a new shaft is the best repair, but that requires a motor split.
     
    Linkin, Apr 8, 2018
    #23
  4. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    GreyImport, Apr 8, 2018
    #24
  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    When I had mine fail with the sprocket skipping off the splines I was also on trailing throttle, going down a hill, fortunately it didn't go all the way off of the shaft - the consequences would have been dire indeed for a rear wheel lock up with all of the traffic on my tail.

    After the temporary repair with it attached with spot welds until it wore through the splines it occurred coming out of a service station - so lucky in both instances.

    @GreyImport is spot on - it is a really important part of the bike - failure at the moment could be potentially very dangerous
     
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    ruckusman, Apr 8, 2018
    #25
  6. Rob1976

    Rob1976 Active Member

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    i am looking at buying second bike for spares. Im not going to do a temporary repair for saftey reasons. I've found through a little research that one of the previous owners fitted an aftermarket front sprocket that is wider than the splines. It also looks liked an ordinary flat washer and not any form of retaining washer was used going by the witness mark on the sprocket
     
    Rob1976, Apr 8, 2018
    #26
  7. risky

    risky risky

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    pom problem- previous owners mistake.
     
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    risky, Apr 8, 2018
    #27
  8. Mike Fulcher

    Mike Fulcher Active Member

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    Hey Bro,(that's a Kiwi term) you aren't going to loose anything by doing just that, weld it on & enjoy riding the bike, as a previous reader said, what have you got to loose? why don't you just replace both the front & rear sprockets & the chain & get another 30-40.000 k's.
     
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    Mike Fulcher, Apr 17, 2018
    #28
  9. Rob1976

    Rob1976 Active Member

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    I understand the reasoning behind welding on a new sprocket but with the amount of damage to the splines there is a lot of free play between the sprocket and shaft. If it was just a case of damaged threads then possibly.
    For the relatively small cost of the replacement shaft I think the risk of breaking down again or crashing isn't worth the risk.
     
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    Rob1976, Apr 17, 2018
    #29
  10. Allan

    Allan Well-Known Member

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    I don't understand why any welding would be necessary or even why anyone would be worried about getting the retaining nut tight enough to hold things in place.
    Surely what matters is the condition of the splines, not the thread. That is where the load is.
    All the Hondas I have owned had a groove around the shaft. A little flat part like a washer with two bolt holes slid on after the sprocket and was rotated about 1/8 turn so that it couldn't slide back. Two small bolts held the washer against the sprocket. There was no force holding the sprocket in. It could float in and out a tiny amount because the washer was a loose fit in the groove.

    ?u=http%3A%2F%2Fimages.wemoto.com%2Ffull%2FSPROCKET_FRONT_RETAINER%2F10063243.jpg
    Is there any reason to suppose that this sprocket needs a lot of force to hold it in place?
    If not, then surely a bit of loctite in the couple of remaining threads would secure the nut and ensure that everything stayed in place.
     
    Last edited: Apr 17, 2018
    Allan, Apr 17, 2018
    #30
  11. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    The thread's holding the front sprocket on look good still to me?

    The problem with the Rob1976s' Hyosung is that 1/2 to 3/4's of the spline's are missing from his output shaft, the locking nut and locking washer aren't the problem.
    I reckon just weld the sprocket to the shaft and not worry about a washer and nut
    Welding the sprocket onto the shaft would require a bit of quick cooling of the sprocket and shaft too, otherwise the output shaft seal will melt/burn away


    To replace the shaft, you'll most likely need someone experienced with the Hyosung 250's to strip the engine, split the case's and replace the shaft,.
    I think you'd be lucky to get out of it for under $350 ish, by the time you buy the shaft, seal's, head/barrel/case and cylinder gasket's, coolant and oil etc etc, and then pay someone to pull the engine down, split the case's swap the output shaft's over then reassemble it all
    I reckon it that was the way your sprocket was fitted then it was put on backward's, that raised section would be there to step the sprocket away from the engine same as the FZR250 3LN's and keep's the rear sprocket alignment correct.
    There is no point having the raised section on the outside

    Allan, your Honda front sprocket wouldn't last too long if 1/2 to 3/4 of the spline's were gone either, the retainer's just hold it in position on the shaft/splines

    [​IMG]
     
    Last edited: Apr 17, 2018
    my67xr, Apr 17, 2018
    #31
  12. Allan

    Allan Well-Known Member

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    I agree. If the splines are badly damaged, that changes everything. I wasn't sure what the Hyosung splines should look like and the blurry photo didn't help me much. :)
     
    Allan, Apr 17, 2018
    #32
  13. Rob1976

    Rob1976 Active Member

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    Yeah the splines are 3/4 destroyed unfortunately. Thankfully I've ordered the parts I need and have the engine out ready for the part swap.
    It should be an interesting repair job. One of the reasons why I bought a budget bike was so I could learn how to repair my own bikes rather than pay big bucks for someone else to get rich off of my lack of confidence/experiance. The other reason was so if I stuff something up, it wasn't on an expensive machine.
    @my67xr only the 2 starting threads are still good, the others are quite rounded and putting the replacement nut on it I could spin the nut by hand despite it hitting the shoulder where it would lock up the sprocket.
     
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    Rob1976, Apr 17, 2018
    #33
  14. Rob1976

    Rob1976 Active Member

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    Hopefully this is a clearer shot of the splines. You can see just how badly they got chewed up. 20180417_205454.jpg
     
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    Rob1976, Apr 17, 2018
    #34
  15. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Take lot's of picture's as you pull it apart, so you'll have something to reference against when putting it all back together.
    And be careful you don't drop the gear's off the shaft when splitting the engine cases, the different thickness shim's go in a specific order between some gear's and sometime's it's hard to work out which goes where
    How many km's has it done ? Might be worth giving it a quick hone and a set of ring's while it's apart ?
     
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    my67xr, Apr 17, 2018
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  16. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    GreyImport, Apr 17, 2018
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  17. Rob1976

    Rob1976 Active Member

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    The bikes done a little over 31000kms when I first got it I replaced a lot of worn parts and did the carbies. The compression was smack on and the plugs looked great so I left well enough alone.
     
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    Rob1976, Apr 17, 2018
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  18. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Are the Hyo's verticle split or horizontal split? If horizontal then you may be able to just take the bottom off to get to the gear shaft, leaving the top end alone.
     
    Murdo, Apr 18, 2018
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  19. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Vertical

    s-l225.jpg
     
    my67xr, Apr 18, 2018
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  20. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Bummer. Rob is going to learn a lot about engines then.
    Go for it Rob, just be methodical and keep pictures, and above all cleanliness.
     
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    Murdo, Apr 18, 2018
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