Hi Erik I am sure that I can speak for all Scott owners when I say how sorry I am that you have had such a disaster. I have never seen such a blow up. I see that there is a hole in the LH crank chamber. We are used to seeing holes in cases like this when a crank has failed, but in your case the crank has not failed. Has this been part of the destruction from above and there is a hole knocked through from above by the piston debris.
It is sometimes difficult to decide what caused a problem, but in your case, unless there was some unusual cracking or weakness in a component, it is more likely to be something done while tuning that looked OK but caused some problem. For instance when Richard put a motor together with very close piston to head clearance and then the head gasket squashed down more than anticipated, so, although it turned over freely, the pistons hit the top when the engine exceeded about 2000 rpm. In your case, if the engine was built symmetrically, then I suggest that you study the still intact RH side to see if you can see a problem. Remember that the piston / rod assembly stretches about 0.7mm when it is revved, so that if you took out port bridges, as we do, then you must allow that the ring does not come into an enlarged open inlet port. We leave stumps to hold the rings in. I remember someone recently telling me that they thought it would be ok to leave the ring / rings unsupported over a wide gap. I am wondering if this happened as if the ring came out into the inlet port, it would pull the bottom of the piston off. Please understand that I do not wish to suggest that you have made a mistake in your tuning. I am just trying to find a logical reason for this. As regards tuning, then increasing the gas passages is entirely logical and if done correctly, certainly will not effect durability. The only possible adverse effect would arise from the increased torque at low medium revs putting a higher load on the crank set. If the rods are shimmed in the pistons, then the alignment is controlled and the loading on the cranks does not have the extra spikes that result from rod wag sideways.
I had a water leak once that went into the crankcase. When I started the engine, it dredged up the water, sent it into the head, tried to compress it, failed and pushed the crankcase apart through the main bearings. I had spent untold hours on that case. Erik, I sincerely feel for you and wish you courage and determination in your adversity.
Very Kindest Regards Roger
