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Help 3LN3 welded sprocket nut

Discussion in 'Yamaha 250cc In-Line 4's' started by Dropdead53, Nov 3, 2018.

  1. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    The front sprocket and chain is a vital part of the system and of course turns at very high RPMs especially at speed .... its external and under load and its very close to your foot ...... now unless you ( meaning any member) have some solution or advice that equates to the sprocket and nut etc being installed as it came out of the factory, or with very little modification, then keep the backyard fixes to your own backyard

    The original poster here might have the knowledge and experience to differentiate between a safe fix and a dodgy one, but lets remember many people , including novice bike owners, may read this and use any advice given.
     
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  2. Dropdead53

    Dropdead53 Active Member

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    On a side note, I’m going to replace the chain aswel, does anyone know how many links? I counted 132 on mine. Just to confirm, I will need to buy a 132link 428 o ring chain?
     
  3. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    428 chains come with 136 links, 520's 530's etc with 120.

    Generally you shorten as required, just don't cut them too short. And get a rivet link, clip links are rubbish
     
  4. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Check the count - should be 130 links

    https://2fiftycc.com/index.php?threads/the-fzr-250.4217/
     
  6. Murdo

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

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    That 15mm dia on the damaged thread is equal to 11/16" UNF which would be an easier die and nut to get.
     
  7. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Did you mean 9/16?

    9/16 UNF 18TPI would definitely go well on that diameter
     
  8. Dropdead53

    Dropdead53 Active Member

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    Update.
    My new chain and rear sprocket have arrived, just waiting for my new front sprocket from litetek to turn up.
    Does anyone know the part number or where I can buy a new gearbox output shaft seal?? And is it difficult to replace?? Is it just a matter of digging the old one out and sliding the new one in?
     
  9. Murdo

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

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    The numbers are on the seal. Go to a bearing shop and ask for those sizes.
    Pull the bush from around the shaft and prize the seal out (clean area first) then using a large socket or pipe tap new seal in.
     
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  10. Dropdead53

    Dropdead53 Active Member

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    Thanks murdo, I’ll clean all the dirt n chain grease off the seal and see if it’s got some numbers on it
     
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  11. Dropdead53

    Dropdead53 Active Member

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    The New front sprocket from litetek turned up yesty arvo. Have I got it on the right way, the large flat side of the sprocket goes up against the bush and then the nut on the stepped side like in the picture?
    A9D8D744-D4E5-4EFC-B1F9-1B9AF10FDF9E.jpeg
     
  12. Dropdead53

    Dropdead53 Active Member

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    Also I managed to order a new genuine gearbox output shaft seal from Yamaha and it was only $23!! However will take roughly 4 weeks to get here from japan I’m having abit of trouble removing the bush from the shaft so I can get the seal out, seems to be on there pretty firm, anyone else removed one before and had trouble?
     
  13. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    The sprocket is on the wrong way around.
    It need's the raised flange on the back so it line's up with the sprocket.
    Are you going to weld the nut on again ?
     
  14. Dropdead53

    Dropdead53 Active Member

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    Thanks, I’ll turn it around the right way.
    Yeah, I’m going to put a new output shaft seal in it while it’s apart and then I’m going to tig the sprocket to the shaft (a few tacks) and then tack the nut to the sprocket and then weld the nut to the shaft on the end.
    Definitely not my favourite outcome but it will get the bike back on the road and will be safe to ride for a few more years atleast.
     
  15. Dropdead53

    Dropdead53 Active Member

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    The old sprocket was well worn out and it was welded. It looks like it had been on there a long while, even though it had the crappiest weld holding it on.
    C9848EBF-45C8-406E-A75E-3AB9CA648A03.jpeg
     
  16. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    You did get the 1HX-17421-02?
     
  17. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    • Informative Informative x 1
    Last edited: Nov 17, 2018
  18. Dropdead53

    Dropdead53 Active Member

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    Negative, I am not replacing the output shaft. My brain tells be I should but my wallet cannot justify it unfortunately.
     
  19. Dropdead53

    Dropdead53 Active Member

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    I feel like this picture in the manual shows the stepped part of the sprocket on the nut side??
    DECBC921-D9AF-44FE-B3EC-ED44D6CA7342.jpeg
     
  20. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    That ring is a rubber vibration dampner on the OEM sprocket's
     
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