RM-I broke one last year. Depending on where it broke, not a whole lot will happen other than engagement RPM significantly dropping. The way mine broke, it was hard to see the break, so I rode it for quite a while before figuring out what really happened. Didn't damage anything, luckily. BTW, my engagement RPM went from 4300 to 3200 when the spring broke. I didn't notice any change in max. RPM.