Hyosung Front Sprocket Nut Issue

It would be a real pain while you enjoy riding your motorcycle on a sunny day and suddenly the Hyosung front sprocket nut comes off the bolt! Unfortunately it happens and it is quite common.  Despite the safety washer lock to the nut as per the image below, this doesn’t solve the issue.

It is quite easy when to spot this, when you feel your bike is no longer accelerating and there is sound coming from the left part of your engine. You only hear the sound if the Nut is still inside the engine cover and if you don’t, it is no longer there.  When you stop, you can see the engine oil is spilling out as per the image below.

* Image credited to Hyosung Facebook group user

When you open the left engine cover, you will see the Nut is off the bolt.

* Image credited to Hyosung Facebook group user

Fortunately, the procedure in replacing wasn’t bad at all. I have never experience such issue thus far. However, I found the method of doing so online. You will need 8MM and 27MM Spanar . The Nut size is 27MM and if you can’t find such size, 28MM will do too. I always carry this along under my passenger seat in case of emergency.

To Fix it, please follow the following steps:

Step 1: Remove the 3 bolts holding the side cover on.
Step 2: If if you have 2 people have one hold the rear brake on.
Step 3: Loosen rear axle nut and loosen chain adjuster to push rear wheel as close to engine as possible.
Step 4: If you have a washer insert it first before putting on the nut to the bolt
Step 5: Once the Nut is tighten, lock the washer to the Nut. Use a flat screw driver to achieve this.
Step 6: Tighten rear axle nut and ensure the chain is properly fitted.

I would highly recommend that you use a thread / Nut locker when you are doing the above. They are quite number of brands out there but the known ones are Hardex and Loctite. One of my friend who uses this never experienced this issue for very long time. He usually uses thread lock every 3 months or so.

Thread locker is a thin, single-component adhesive, applied to the threads of fasteners such as screws and bolts to prevent loosening, leakage, and corrosion.

Please only use Color coded blue. (Medium Strength)

Directions:

1. Nut and bolt surfaces must be cleaned and dry.
2. Shake the bottle before use.
3. Apply sufficient thread-lock to the bolt
4. Assemble the sprocket nut to the bolt and remove excess thread lock.
5. Allow assembly to cure in a few minutes and full strength after 24 hours.

I didn’t manage to record a video. However, I found a video online as per below which will give you a rough idea on how this works.

Whilst doing this, please also check sprockets for wear.  If they look hooked or worn, you’re going to have to change them.  If you can pull the chain off the sprocket, change the chain and sprockets.  If you have many tight spots – change the chain and the sprockets.

If you have any questions, drop them at the comment box below and feel free to share this article via the social buttons.


6 Responses

  1. Stephen says:

    HI, B4 putting on the washer check the sprocket is pushed on the splined shaft firmly.
    The locking washer ALSO needs to be on firmly so the “splines” are engaged (the washer must NOT turn on the shaft) b4 the nut is tightened and washer bent against nut = .

    THE BENT WASHER LOCKS THE WASHER to the NUT
    THE WASHER ENGAGED IN THE SPLINES STOPS THE WASHER FROM TURNING
    THIS LOCKS THE NUT ONTO THE SHAFT via the BENT WASHER and the WASHER SPLINES ENGAGING WITH SHAFT

    If the washer splines are NOT engaged with the splines on SHAFT then NOTHING is LOCKED to the shaft AND YOU just HAVE washer locked to nut = will work loose
    (I know I “fixed” my son’s 250 and 20km later it had fallen off because I didn’t assemble it all carefully duh )

  2. Chris (Administrator) says:

    Hi, the size of the Nut is 27 and when the nut is off, the washer that holds it will be off too and that is why engine oil will be dripping.

  3. Erik says:

    the size is M16 x 1.5.

  4. todd says:

    What size is the nut? And why does it leak oil? Thanks.

    • Chris (Administrator) says:

      Hi, the size of the Nut is 27 and when the nut is off, the washer that holds it will be off too and that is why engine oil will be dripping.

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