Mercury Mark 20

[Aidan Smith]

Working on a 1954 Mercury Mark 20.

My ring gear to throttle assembly seems like it is awfully stiff to turn. I have put a touch of oil on the gears, but it does not seem like it has loosened up any.

Is there some adjustment that I am missing?

The rest of the motor works fine, but the shifter seems to enjoy being in the “forward” position, and easily moves from N to F. I’m thinking that it will be more secure once the engine is running, but I’m not 100% sure.

 

Thanks!

"Shells sink, dreams float. Life's good on our boat."
1931 Johnson A-50
1950 Mercury KF-7
1951 Mercury KG-7
1956 Johnson JW-12R

[PM T2]

The magneto plate needs occasional lube as it has to also slide as it rotates. The friction area is beneath the magneto plate. Old oil and grease deposits usually gum it up. Figure out how to get some penetrating oil in that area and things will loosen up.

PM T2

He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...

[Buccaneer]

Yours might be one “known” for jumping into “Forward” when idling in neutral.
I have some notes from the board save while working on a Wizard Powermatic 12,
which was based on a Mk 25.

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billw
US Member – 2 Years
Replies: 2056
Topics: 65
October 17, 2022 at 5:58 am#267768Reply Thanks Quote
For all the bad-mouthing that Mercs get, you’ll never see one jump OUT of forward, like OMCs do. There’s a strong spring in the prop shaft that constantly has forward pressure on the clutch dog. The engine stays in neutral or reverse, counteracting this spring, in two ways. One is by steps on the shift cam in the lower unit, which is fine when the engine is not running but not substantial enough to hold securely when the engine is running and shaking. The other is by a ball and detent arrangement at the top of the upper shift shaft. You may be able to see it near the aft end of the shift handle. This is a more positive detent than the clutch dog has; but sometimes the ball gets stuck from corrosion. My bet is, that’s where the problem lies. Another more subtle problem comes from wear in the spline connection between the upper and lower shift shafts, and/or a twisted upper shift shaft. These two conditions create a situation where the clutch cam detent and the upper ball detent do not coincide with each other, meaning that the two detents are basically fighting with each other, as to where the neutral and reverse actually are. When this happens, the big spring wins and it shifts into forward. Add to all this, the reverse lock mechanism. It too, has a ramp that has a tendency to favor forward. This ramp is adjustable, so you can try messing with that. But my money is on the upper detent ball being stuck.
billw.

Prepare to be boarded!

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