Some failures on the Yamaha 1.8L engines involve the crankshaft being pushed forward in the engine. This can be caused by a number of reasons. Some may include:
drive coupler coming loose.The PTO transfer shaft coming loose.
The nut on the end of the pump driveshaft coming loose. These failures can push the crankshaft forward and damage the thrust plate area inside the engine block. As a result, the engine block is damaged and needs to be replaced. ($2800 retail for a new engine block) Riva has developed a replacement bronze bushing that can be fitted by machining the damaged area of the engine block. This can save the engine block & dramatically reduce the cost of the repair. A qualified machinist should be able to handle this install without any issues.