OK, here are some pictures and explanations of this issue:
This is a picture of a typical reverse gear out of one of these units. Notice the shiny/galled looking area, this is the area that rubs on the aluminum prop shaft/seal bushing. Looks like the metal has gotten hot. Look carefully at the slight raised rib near the hub of the gear, the bronze thrust bushing I found must be carefully oriented over this rib or the prop shaft will bind up while the gear/shaft/bushing/bushing seal is installed into the gearcase.
This picture shows the reverse gear with the inexpensive bronze thrust bushing properly installed over the reverse gear. Notice the shiny inner aluminum rib on the prop shaft bushing/seal housing, this is the surface that the reverse gear normally "rubs" on. The friction and heat developed during normal operation slowly wears this aluminum surface down resulting in the burned gear lube often times seen during servicing along with the excessive prop shaft end play. The excessive prop shaft end play results in shifting/gear jumping problems, this includes the ball shift style gearcases. The excessive prop shaft end play is hard to detect because the clutch dog spring is preloading the prop shaft. The only way to really evaluate the prop shaft end play is to disassemble, remove the spring, then reassemble and evaluate prop shaft end play. Unfortunately, I can’t post the original dimension of this aluminum rib because I don’t have any of these prop shaft bushing/seal housings in new condition. This unit had almost 1/8" end play, the new bronze thrust bushing I found is about 1/8" thick as well. Once assembled with the thrust bushing, the prop shaft bound up, so the aluminum rib on the prop shaft bushing/seal hsg had to machined down about .020". Our chapter is so lucky to have DAVE BONO as a member, he popped the aluminum prop shaft bushing/seal hsg in his lathe and machined about .020" off in a matter of minutes. Now, with the new bronze thrust bushing installed, the prop shaft has about .010" end play. Please don’t be misled by this picture, it shows the bronze thrust bushing already in place on the reverse gear, I should have take a picture of these two pieces without the added thrust bushing. Remember, the bronze thrust bushing must be properly oriented over the raised rib on the reverse gear.
This picture shows the reverse gear with the bronze thrust bushing properly oriented the gear’s raised rib.
This picture shows the reverse gear, added bronze thrust bushing, and aluminum prop shaft bushing/seal housing properly assembled on the prop shaft.
This picture shows all the pieces IMPROPERLY assembled. The bronze thrust bushing is not properly oriented over the raised rib on the reverse gear.
Another picture of the pieces PROPERLY assembled.
This is a picture of the assembly reinstalled (bolts gently seated) without the clutch dog spring to evaluate prop shaft end play after the update/repair. This unit has about .010" end play now instead of almost 1/8". Again, it would be best to figure out some way of "pinning" the bronze thrust bushing to the aluminum prop shaft bushing/seal hsg so the bronze bushing does not rotate on the aluminum surface. But, there seems to be less friction between the gear and thrust bushing, so the thrust bushing seems to rotate on the gear face naturally.
I will post a link to the site where I found these bronze thrust bushings, they cost only $3 apiece. Much less expensive than replacing the aluminum prop shaft bushing/seal housings that are no longer available new. I’m hoping this repair will reduce the friction and minimize friction generated gear lube failure as well…
Don
