I still have stock '13 shafts. My C3 bottom pulley required I use the bolt and washer to get it to seat the first time. I still need a couple of small tire irons to take it off but it will tap into place now.
I don't think my stockers were as loose as that vid but they were loose enough that I didn't need any special tools to R&R the belt.
The fit on the splines is better when tight but it is still the torque applied to the shoulder of the shaft that holds the assy together. If you needed a 2 ton press to assemble you would still need a torque applied (or welding) to keep it assembled.
How long to fail without torque on a pressed assy would be determined by how many times unnecessary lateral forces are applied however strong or weak they may be.
The top bolt does more work but the diameter of the pulley is less so unnecessary lateral forces are less. Lost torque up there shows a different failure. The top bolt holds the pulley, disc and inner bearing race tight to the shoulder of the shaft. When torque is lost on this assy usually the inner bearing race spins and ruins the shaft.
IMO the reason some people have a failure and others don't is because some sleds have more unnecessary lateral forces than others. A production thing.
C3 in their instructions recommends checking the torque on both pulleys after the first and second rides, then 500 miles then every 1000 miles. They didn't need to tell me that because of what I found when stock in '13. I think my sled was maybe a worse case scenario for unnecessary lateral forces but I finished 1700 miles with zero failures.
I'm a "check the nuts and bolts" guy. Sometimes hey take a snug and stay there, sometimes twice. I figured the 4th time with the pulley bolts meant I needed more torque or something. They had already stretched, (to check this, take a good bolt and a suspect bolt, put then thread to thread and look up at a light. If the threads don't match throw the bad one away) and it wasn't from poor calibration on my Snap On torque wrench.
Getting rid of unnecessary lateral forces was a quest, but keeping the torque was easy.
Only need to go up one grade in bolt, maybe 2 or 3 grades in supplier and IMO a better bell washer than stock.
I use a Doo XM secondary clutch washer. It's 2 or 3 times as thick and has held it's shape for many torques. At 45 ft lbs it is not flat yet. I use 60 ft ibs which is the high end of allowable torque for the upgraded bolt I use according to the manufacturer and that flattens the washer.
Even with that torque my bottom pulley needs one more snug and top pulley two snugs until set after reassembly. In my case I think that is because I am torqueing steel to aluminum.
Hope it helps if you busted one and if your near by give me a PM 'cause I had to buy a bag of these bolts.
