Re: Johnson TD20 / TN26 etc. – T-shooting Part 2

[legendre]

Garry, my new best friend.. 😉

quote Garry in Tampa:

That is a drain for oil that gets past the top main bearing. A slinger ring on the crankshaft throws the oil into a groove above the bearing that is channeled to that pickup tube. An early example of recycling. The center bearing is the slow speed rotary valve. The piston skirt acts as the valve for high speed operation by uncovering the third port behind the carburetor. Dammage or excessive ware to the piston skirt will efect the power output.

So you’re saying that the flow is opposite what I’d assumed? Excess oil leaves the crankcase and is.. returned to the crankcase to be burned.. via the slow-speed carb? Please forgive, but that doesn’t make much sense to me. If it’s already in the case to begin with, why isn’t that good enough? Why re-circulate it?

The middle main is lubed by the rotary valve hardware, the lower main by mist & gravity.. but gravity fights against lubing the upper. So where does the excess oil that would likewise pool at the lower main go – doesn’t that need to be removed as well?

Now depending on timing, the pressure in the case can be at, above or below atmospheric. If anything, I see more of a push-pull flow in that tube, rather than a unidirectional flow from inside to outside. Anyone else chime in on this?