Blown Crank !

[John U.]

1990 Yamaha Supetjet 650...A pin fell out on crank/connecting rod assembly and got up into the piston and chewed them up. At first I thought it was electrical because it would start fine and then just quit.{seizing, I would find out} I had previous trouble with the kill switch.
After taking it in, the fellas showed me that damage. Ball bearings were comming out. At this point it's no good to me. I love riding it though. I only paid $900 trailer and all from my buddy.
What are my option's here? Do I do the work on this one to rebuild or am I better off getting a new motor? Parts are available I know from Yamaha and elsewhere but the prices are outrages{sticker shock}. Are the rebuilt SBT's bolt in and go? What are my options for beefing up the horse power{fun}?
Bullraider directed me to this site. Thanks fellas.

[Bryan Glynn]

You can certainly do it yourself, although you will find that you will spend the same or more as what you would have for one fo our blocks, and you won't have a warranty. Yes, our blocks are bolt in and go.

You obviously need a top-end, and I would suspect your crank is shot from your description, if you have lower bearing failure. Even if it was just a wrist-pin bearing that went, because you've repeatedly seized it, the crank is probably at least weakened, and I wouldn't trust it at this point.

As for power, honestly I wouldn't put any money into a 650 for serious upgrades. It would be money better spent on a later model like a 701, with much more potential and aftermarket parts available. Yes parts are there for a 650, but by todays standards, the results are pretty weak.