i wonder what cause this engine to broke the front crankshaft near the centex clutch?here the pic of it..anyone know what cause this?

Damn! Never seen anything like that. Looks like the break happen where the thread ends. Could be just a weak part of the shaft.

I only see two ways to break it there.

1. Over tightening of the nut (we're talking impact gun levels of torque).

2. Manufacturing defect (micro-fractures in the metal).

There are other things that could break a crank like a badly out of balance flywheel/clutch assembly but I would expect it to break in a different place for that.

I once broke a crank shaft like that, the engine slipped out of my hands and landed right on the shaft

thanks guys for helping out here..i just totally blank when this happen..but this my 2nd engine that broke crankshaft..the 1st one i broke the middle @ the intake last year..now my ninja..is nova crankshaft can fit on ninja block?since i just replace my front and rear bearing with ceramic so i try to find what crank can be fitted in it..