Broke My Frame!

Bicycle frames are NOT designed to cope with substantial vibration,least of all those made of strong but metal fatigue prone thin wall Cro-Mo tubing.The thick wall old fashioned mild steel frames stand up best.Rack mount systems tend to transmit less vibration to the frame (with proper mounting).Losing control&crashing can be very dangerous with traffic around.The saving grace is that the fatigue crack is usually not yet complete before it becomes apparent that something is amiss,But a frame can unexpectedly fail catastrophically when overstressed (braking a hard landing etc).Get some life&disability insurance.
 
Looks like it broke right where I'd expect it to (if it's going to), at the motor clamp. Doesn't look like you drilled the frame for the mount, would make it even more prone to breakage. The tube's just not designed to pick up the loads that the motor puts there, especially if the clamp force causes the tube to crimp at all and along the sharp edges of the mount... I'm welding up a mount for mine that will distribute the load over 8" or so of the tube, hopefully to minimize this kind of failure.
 
The best solution is to stiffen the tube with a sizable U bracket that fits over it, that has a lossy rubbery material between it and the tube to absorb the engine vibration.Fatigue failures are caused by repetitive flexing
 
Might just be the case of a defective frame and you just sped up the time for the break to happen.
 
I think that is wishful thinking,frame defects usually occur at welds or lugs, not in the middle of a tube, where the engine mounting hardware is attached.This is an obvious a fatigue failure,due to engine vibration.
 
I think that is wishful thinking,frame defects usually occur at welds or lugs, not in the middle of a tube, where the engine mounting hardware is attached.This is an obvious a fatigue failure,due to engine vibration.

Your probably right, but there is still the off chance that the tube has an anomaly right in that area.
 
Of course there remains that unlikely posibility,but I would base any actions and conclusions on the by far more probable cause.A microscopic examination of the fracture could dispell all doubt.
 
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