This post takes you through the steps to change the front sprocket of your Rotax Max 125 engine and how to remove and re-install your clutch drum.
Once you notice that your front sprocket is worn, it's a good idea to change your front and rear sprocket and chain at the same time, as they will usually wear at the same rate.
Torque wrench able to do 110Nm (optional)
Tools required for this job are:
16mm or 17mm ring spanner
5mm allen key
38mm impact socket
17mm impact socket (optional)
5mm in-hex socket (optional)
Rotax sprocket holder & locking tool for ring gear
Step 1 - Remove the clutch cover by undoing the 3 M6 cap screws, loosening the cover.
Step 2 - Insert the Rotax locking tool into the ring gear to lock it in place.
Step 3 - Remove clutch retaining nut and washer.
Step 4 - Remove clutch drum from engine.
Step 5 - Put the clutch drum into the sprocket holding tool and use the 38mm socket to remove the sprocket retaining nut from the drum.
Step 6 - Remove front sprocket dowel pin from clutch drum and insert the new sprocket into the clutch drum (don't forget to re-insert the dowel pin). Use Loctite on thread to retain nut on sprocket.
Step 7 - Insert sprocket into sprocket holding tool and tighten the nut to 110Nm.
Re-installation is the reverse process of the above steps.
Firstly, install the thrust washer, o-ring, bearing, then the clutch shoe, retaining washer and finally retaining nut (don't forget to use some Lactate on the retaining nut).
Lastly, re-install the clutch cover and you're all done...