Hi Roger,
This time I took even greater care to do everything according to the book. I knocked up the crank with great care and used a new nut and bolt. I measured the play several times (in and out the frame) and it was 0,3 mm, so perfect. I gapped the rings at 0,009″ and doublechecked if there was enough left of the bridges to support them. There was, even after assembling and tightening down the block. I did not find a single piece of ring so far so I guess this is not the problem. I also shimmed out the little ends with the appropiate play so there was no sideways movement. The other piston by the way looks absolutely fine through the rh transferport.
To be honest, I can think of nothing that can cause the piston to turn on it’s axle. As you can see the gudgeon pin is still in its hole in the piston. As I cannot imagine the pin being sheared, so the little end must have twisted the same amount…
And the hole in the casing? It must have been the debris, but on the other hand, most of it (at least the larger parts) I took out from the space below the piston and not from the well where the smaller parts were…
The only thing I can think of that might have caused the trouble is the amount of space around the piston skirt at bottom stroke in the casing. I enlarged this while this was a 500 casing to take the Silks and made sure it was enough. While turning the engine over and during the first testrun in my street this space was enough. Maybe the piston expanding while running seized here? But to be honest, I think this not the case too as I made sure the play around the piston was quite large.
But I guess you are right, I will not know it untill I have disassembled the motor. At this moment I do not know when that will be. The Scott Run is in two weeks and allthough my bike obviously does not run I might take it there anyway just to make photographs with the other Scotts (a Dutch classic motorcycle magazine has asked me to write an article on the run and make pictures and I would sure like my Scott to be in it). So, you all might have to wait for a few weeks to see what was wrong.
But on the other hand, I am not sure I can wait that long…
On the one hand I do hope it was a stupid mistake on my account. That way I can blame myself. If it was a component weakness it would be extra sour for me after all the hours spend on flowing the casing etc…
To be continued for sure!
Erik
PS: The night after this happened our daughter was crying a lot at night keeping us awake (as if I was not awake already trying to figure out what went wrong). When we just had about had it with her I took her out of bed. The way she then looked at made me forget alle the crying instantly….
The same with my Scott. Even if it blows up on me, I still just love it…. Any other bike I would have given a gigantic kick but not this one.
Stupid isn’t it…
