russell.k said:
It happened in a whoop or roller section
The most common cause of this type of rod failure or as Mike Perry from Kibblewhite calls it "energetic disassembly", is connecting rods that break near the small end of the rod . Usually seen as a plastic failure of the rod.
Rod failures often occur when a rider shuts the throttle completely from high rpm. It's more common to see a rider break an engine entering a corner or in a whoop section than it is running down a long straight.
Closing the throttle stops the cylinder from filling the cylinder completely which effectively lowers the cylinder pressure.
It's a lack of pressure that is the problem. If you stop the cylinder from filling there is a lack of pressure above the piston as the piston decelerates approaching TDC. When the cylinder is full and firing the combustion pressure works as a cushion to help slow the piston down. Without that pressure the rod is subjected to a much greater tensile load and often times a plastic failure of the rod near TDC occurs.
The same thing happens when you hit the rev limiter. It's not the rpm that kills the rod and the crank bearings it's a lack of pressure above the piston that is the problem. If you stop the cylinder from firing there is very little pressure above the piston as the piston decelerates approaching TDC and the rod gets stretched like Silly Putty. Just like Silly Putty if you stretch it far enough and fast enough it will break.
This is most often seen when up a new top end is done on a crank that is past it's service limit. If you keep on top of normal parts replacements none of these issues are ever likely to come up.
The point being, if you stop the cylinder from firing at peak revs it puts the crank, rod, main bearings and piston in harms way whether you cut the engine with the ignition or the fuel.
That said it would be possible with a proper engine management system to roll back the ignition timing, or cut fuel in a progressive way to slow the engine down rather than just killing combustion. But, it's important to remember that a large number of engine over-rev failures that I've seen were caused by riders mechanically over-revving the engine by driving it with the rear wheel (downshifting at high rpm, etc) . There is no rev-limiter, no matter how smart it is, that can stop riders from being stupid. The OEMs are in the business of selling parts so a simple rev-limiter might be better for business than a complex DUMBASS-limiter.