Also, check that the water cooling inlet is not blocked. This can happen easily if the engine is used in water containing a lot of weed or algae. The inlet will always be at the lower end of the engine shaft - i.e. below the water level.
Peter Tyler
February 2008
your impeller is located in the bottom end, theres 2 bolts holding the gearbox on, be gentle if they wont turn try some heat.once undone the box should just pull down, a plastic hammer may help if its tight. theres a copper water pipe running up to the engine, fix your garden hose to this and apply a little water pressure the water should circulate round the engine, if not you may have a block running round the head