I have a BS 60 with a SK.91. It flew great until two weeks ago when I had a dead stick landing. I was able to land without any damage, but noticed that the prop and spinner hub was missing. No big deal and got a new prop. But upon closer inspection, the engine must have thrown a rod or something. I can spin the crank shaft about 180 degrees and it makes a "clunking" sound coming to a stop. I pulled the muffler for a look inside and the piston does not move at all when I turn the crank shaft. It's stuck in one position. So something is definitely broken inside. I'll have to call Kangkeusa tomorrow and see what they can do. Hopefully they honor the two year warranty. I'm not sure if I want another SK91 or just ask for a refund.