Re: Merc guy looking for advice on Johnson

[Don]

Like others have said, the smaller gearcase is the weak link on this otherwise bullet proof engine…Decent driveshafts are getting tough to find as well.
If it were me, the first thing I would do is drain the gear lube and inspect. If the gear lube is milky/watery, I would pull the gearcase. Once the water pump is removed, the driveshaft should just pull out, it is splined into the pinion gear (unless someone has replaced it with an older style keyed driveshaft/pinion set up. Once the driveshaft is out, have a look at the lower area just about the pinion where it rides on the bronze bushing in the gear housing. Most of these driveshafts will show some minor wear in this area, but you are in trouble if gouging/wear is excessive.
Needless to say, you will want to check compression, it won’t have too much, about 80-90PSI is all. Everything else is standard service stuff for these engines, ignition, fuel system….Unless it is a salt water engine…
Once rejuvenated, you will really enjoy this 10hp….