2013 450 broken hub

I've found posts on here regarding broken hubs and loose sprocket bolts or chain too tight but listen to this one.  


I've been riding well over 20 years and have never broke a hub,  had 6 different 450's and race +25A,  until my 2013 YZ450f..  Broke the first one a month ago and thought a rock caused it,  new hub all new chain and sprockets and busted the &%$#@!er again.  


I read the posts on how to not tighten your chain to much but there's a fine line between to tight and so loose its actually grinding away the inside of the frame and making so much noise you can't ride normal.  


The first hub broke on a landing and the second one over acceleration bumps and ripped the sprocket completely off the bike. 


I've always loctite the sprocket bolts.  Are these new hubs just cheaper built?

No, they aren't.  You seem to doubt the manual specified chain adjustment specs.  The chain REQUIRES a minimum of 50mm (2.0") of slack, measured as shown, when the bike is on a stand. (max is 60mm or 2.4").  If you have less than that, the chain will not be long enough to allow the swing arm to pass through the point where the centers of the output shaft, swing arm pivot, and rear axle align, and something has to flex, bend, or break if you force it past this point, as would happen on a jump landing or a big G-out, or even a significant bump in the road.  Simple geometry.


The most likely component to yield a significant amount is the rear sprocket.  Sprockets like the older Ironman that don't have a continuous ring at their inner diameter can aggravate this by focusing the strain on a single mounting bolt tab.




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