I traded my tensioner wheel out for a skateboard wheel i modded so I could have bearings also my old tensioner wheel pin was de-threaded so i switched it out for an american bolt and nut. Well the lock-tite and crimping of the threads came loose and the nut started backing off and eventually the wheel tilted enough to rub the tensioner bracket. This catching action I believe started pulling the chain and then engine since its attached. Eventually enough tugging occurred to rip one of the bottom brackets bolts thru the bracket and break the other bolt flush with the engine. I cant get the broken bolt out to replace the bracket and broken bolt, So I flipped it around so the good bolt and good bracket hole are together, so I have one bottom bracket bolt holding the engine. My frame is fat so the bottom bracket is a bolt thru the frame then a stack of washers as a spacer then a back bracket for a frame mount flipped upside down and a third hole drilled for the frame bolt (not my build). It could also been caused by friction but when the bottom bracket failed, while pushing, every time the tensioner wheel would catch the motor pulled out of the frame. I dunno im going to ride it with 1 bottom bracket bolt and see how long it lasts. but im switching out the skate wheel for a new tensioner wheel since it comes w the pin and I`ll put proper speed bearings in if need be to get what advantages come with a skate wheel. All in All very depressing to lose an entire operating engine to a 2 inch piece of chinese all-thread. THinking back i wished i would have switched those bolts out for something that bends instead of breaks,,,,like AMERICAN STEEL wtf these chinese bolts are like pot metal.