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Re: Yanmar super vibration
Glad to have helped.
The 2GM20 had a single double-ended cone (I still have my old one), although I'd call it more than a "washer" - it weighs about a pound, the inside hole is a spiral thread that rides on the shaft; the outside is ridged and tapers toward each end, with a slot around the middle circumference. The stainless shifter dog rides in the slot (replaced at the same time) and moves it forward or aft, so the cone nestles into either of the counter-rotating drive gears. The spiral thread forces the cone to fully engage as a friction fit into the selected gear.
The shop I went to first "fixed" the knocking problem by "lapping" the cone into the gears, which lasted for a only little over one season (May-Sept this far north). When it recurred they lapped it again, which was a complete waste of time and money.
I just took a micrometer to the old cone, and other than some letters stamped into one end, can see no difference between fore and aft. I'd say (with a BIG caveat that I'm an electrical, not mechanical, engineer) that you could probably reverse it and use the less worn "reverse" side for "forward". I also wonder if milling a little off the face might let it engage further into the drive gear, depending on how far the shifter dog will let it go.
I also recall that several seals and such were "peened" closed and had to be replaced each time the transmission was opened.
Another caveat - on my C&C33, the external shifter arm had been repositioned 180 degrees to work with the Edson pedestal shifter (swapping push-pull/fwd-reverse), and when the second shop who correctly replaced the clutch cone reassembled it, they put the arm back in the "usual" position - now reversing forward and reverse on the shifter. Discovered that on the first day of vacation, so I drove the boat that way for a couple of weeks until I could pull the tranny again an have them re-reverse it (whence I learned of the seals that get changed each time). Make a careful note of which way the external shifter arm is pointing before disassembly.
In retrospect, make sure to leave these transmissions in REVERSE when sailing so that the prop forces the cone to engage reverse and stop any rotation. If left in Forward, the prop will turn the shaft spline in the sense that slightly disengages the cone, letting it rotate while still nested in the drive gear, slowly wearing it away. (It was interesting driving through Canadian Customs in reverse while I was unable to get it to re-engage in forward.)
1998 Jeanneau SO45.2
Last edited by redline; 04-15-2014 at 09:47 AM.