R7 you should look at the sheve on main clutch shaft. look for paint worn off or polished steel in bottom of sheve groove. those sheves pulled a lot on N7 R7 R70. My R7 did the same thing, milo was a real load on everything. Replacing belts will help for a while but with the edges of sheve worn really bad they will work down in groove and start to slip after a little wear sets in. Another thing we did to N7 R7 was replace idler pulley on same belt with larger diameter pulley. That would put less backward bend in belt reducing splitting and streach spring just a bit.