Re: Johnson 10 hp 1957 onward
Hi Boleget,<br /> With the powerhead items they improved the motor over time. They added heftier bearings at the wrist pin end of the con rod, went to a smaller flywheel, improved oil scavenging, etc. You'll find a lot of the '50s 10s with "ovaled" wrist pin bearings as they would wear at that point, leading to knocking and eventually failure. The later rods had a wider bearing to improve distribution of the forces. The lighter flywheel put less strain on the crankshaft.<br /> With the lower unit, they were looking for economy. They lightened the motor a bit by going to the smaller lower unit and made it cheaper to build. It reduced the potential longevity of the motor as you'll find a lot of those 10s (and the later 9.5s) that chewed up the units. They work fine in normal operation, but they can't take a ton of abuse (which is more like "real" world "normal" operation). A little ding in the prop to throw things out of whack might not bother the bigger unit as much as it does in the smaller unit, etc.<br />- Scott