Almost all the time I work on these, the bushing has backed it’s way out of the orifice, leading to the air leak. I’d say about 50% of the time the o-ring has vulcanized and is worthless. Either way, I replace the o-ring. I use the special tool to knock the bushing out and the 2nd special tool to reinstall.
Generally the only thing I see happen with removal is a slight ‘nick’ to the bottom of the bushing when I have to strike it once or twice hard to jar it loose. What I would caution folks of is re-installation. If you drive the bushing down too far, it’s not that hard to crack the gearcase housing orifice on one that has become widened out. So say you go to reinstall and don’t feel a ‘snug’ fit of the brass bearing, so you strike it a couple more times. Now you have a cracked orifice casting.
The bearing installer tool lends itself to seeing how snug the shift rod will be because you are already putting the bearing and o-ring on the tool, so as you strike it you can see how tight the shift shaft will be once reinstalled.
Not sure why that casting would expand out (I mean, I suppose anything is possible with something that is 50 years old and used repeatedly every time the motor is run).
In terms of tightness of the shift rod depending on how much ‘smoosh’ there is with the o-ring, I think experience tells you how much to drive down that bushing. I rather have a shift rod that is very snug (not impossible to move, of course), and when I reinstall the shift rod I usually spray a little WD-40 or the likeness and rotate the rod to prevent o-ring damage. The thing is going to be coated with gearcase oil from the bottom side once you fill it back up and everything is swirling around in there with the gears anyways and/or exhaust oil/unburned fuel from the top side.
All of us are the ones who are keeping these motors in service; these designs lasted 30, 40, 50 years before needing some help, we’re just the ones who end up carrying out the service they need.
I’d be interested in hearing recommendations for where to buy the replacement o-ring in bulk (say, 50 unit packs). I buy the 5-pack replacements as a sierra dealer, but I know there has to be an even more affordable option out there. I mean, an o-ring is an o-ring…right?
