When changing oil on these 600cc's is very easy to make yourself some double my introducing air into the oil system. The Oil pump doesn't create a strong vacuum and cannot push air out - thus starving the engine without the oil. This applies to all Yamaha's TT600 XT600 and even older models of TT500. Easy to miss - big damage to deal later. Always drain oil by the dedicated oil drain plugs. If you rebuild motor - always bleed the oil system.