Hi Samir. I would have to estimate somewhere around 20 hours. I have to be honest – I am not familiar with the differences between the Senior and Junior motors. Regardless, if you’re intending to disassemble the motor, and still want to be legal for Rotax Max events, it has to be done by a certified shop. Otherwise, you would be running in a less strict TAG class. The other option may be to buy a legal Rotax Junior motor, and either sell the motor that’s on the kart for parts, or repair it for eventual practice or TAG use. FYI – The only certified shop I know of that’s relatively close by is the OVRP shop.
I’d love to fix it, but baby and house priorities overrule kart tinkering….for now.