I was wondering the same thing. I infact bought an O ring chain but it would not fit due to the lack of space between the front sprocket and engine case. The only way around this I would think is to fit a smaller front sprocket (if they are available) and then if you want to keep the same gearing you will need a smaller rear sprocket. Not sure if they are available either. I have a standard (quite weak looking) chain on mine and given the power of the motor expect it to stretch a fair bit once I am using it regularly.