Today I was going up the Roseville bridge and all of a sudden the engine began to behave like someone was hitting a hammer inside it and making a LOT of very bad noises so I immediately pulled over and shut the engine off and got it towed. The noise sounds so serious that I'm not sure it's going to be salvageable and began to do some research. Apparently such a noise may be a 'bottom end bearing' failure from oil starvation/lack of lubrication (from my side of the road googling). I don't know how this could have happened as I checked the oil last weekend and topped it up. I had been riding the bike all last night and all today and it was fine with no issues until the last few moments. The only thing is that unfortunately the last two rides have been through the heavy thunderstorms in Sydney and I believe that water may have got into the engine somehow and spoiled the oil causing the damage What would the approximate cost for a GS500 engine replacement be? The one I've got is special so buying another isn't really an option.