I have a beast of a motor in my 86 FXRS, 96" S&S with 6speed Baker and 2" Open belt. I just raced the guy I bought it from, he was on his V-Rod muscle with vance hines pipes and tuned. My bike kept up with it no problem. Simply amazing.

Alex from Indian Larry's shop built the motor and the fasteners from the motor kept breaking so he drilled out the tranny so that they fasten like the Softails and used L9 fasteners. One of the bolts broke again. Can I get stronger fasteners than L9 or are they too brittle and that is why they are breaking.

Help...

 

The bolts are much stronger than the aluminum they are in. It sounds like you may have some movement/flexing. Check the back of the belt drive plate for movement marks. We have 140+HP engines that do not have that problem. I am sure if you take things apart carefully and examine everything carefully you will see where the movement is. Then we can figure out a cure.