The mazda motor was built just for the industrial application in fork lifts. Granted it was a automotive based but things like the valve springs which were just strong enough for a 2500 rpm motor operation is just one of the reasons this motor is so durable. Compare a mazda automotive valve spring with the industrial motor valve spring and you see the differance. I have ordered aftermarket heads and they all have the automotive spring.There were other things that was done to tune the motor for this application and it was done right. RIP Mazda