I was running my two cylinder shay yesterday and it derailed cause I was fooling around with the track. The rear shaft slid out of the drive and flopped around for a few seconds. I put all back and it was running fine. I noticed a whisp of steam comming from the drain valve under the steam oil tank. The drive shaft evidently struck the valve and opened it enough for the oil to drain out. Had I not noticed that the unit would have run out of steam oil and possibly sieze as it was early in the run. Just something to check after a mishap. Nick Jr