Just Got first boat; Shift Shaft Question

briaineo

Seaman
Joined
May 13, 2013
Messages
58
Hi all

I've just got my first boat, Mercury (year 1974) 402

Have a question on the shift shaft linkage mine does nothing when I move the lever, the arm under the carburetor rotates, (have carb removed for cleaning)

Have the lower unit set to neutral, the tapered cam towards to bow.

Is it correct that the shift shaft only moves up and down? And if so how does the mechanism work?

Any help greatly appreciated

thanks
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,687
Re: Just Got first boat; Shift Shaft Question

I'm not familiar with the 40 hp engine. Having had a 7.5, 9.9, 85, 90, and 115 that I can remember, all had a cam driven shift mechanism. In the front of the lower unit (the part from the big plate over the prop down) is a splined shaft that is twisted to move the "shift cam" through the gears. This shaft is positioned by a shaft (female bottom end) that goes up through the midsection and stops above the clamp bracket mounting the engine to the boat.

There some sort of arm is attached to the shift lever/linkage whereby the shaft is twisted to change gears.

With what you said, it seems your shifter shaft has become disengaged from the shift shaft (male) in the lower unit. Probably will require dropping the lower unit to reattach. But that's not all bad. You can check your water pump impeller while it's off.

Get a manual.

Mark
 

briaineo

Seaman
Joined
May 13, 2013
Messages
58
Re: Just Got first boat; Shift Shaft Question

Hey Mark

You've been a great help, one thing that is puzzling me; there is a shaft the comes down the back of the outboard the moves up and down; It seems to rest on part of the gear change mechanism. Whats the purpose of this?

I do have a manual but a basic beginner to all of this. I changed the impeller. But the gears didn't work before that.

hope you were not affected by the tornadoes
 

carholme

Rear Admiral
Joined
Sep 4, 2010
Messages
4,845
Re: Just Got first boat; Shift Shaft Question

What is your engine s/n?

Gerry
 

GA_Boater

Honorary Moderator Emeritus
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May 24, 2011
Messages
49,038
Re: Just Got first boat; Shift Shaft Question

The up/down arm you see is probably the reverse lock shaft driven by the reverse lock cam on the lower unit shift shaft. The shift shaft rotates, it doesn't move up and down. I think Texasmark is referring to the shift cam inside the lower unit. The reverse lock cam and the internal shift cam are the only cams.

You should be able to drop the lower unit and rotate the lower shift shaft to see if you can engage forward/neutral/reverse. You will be dropping it again anyway. I think your shift cam is mis-indexed.
 

merc850

Commander
Joined
Jul 7, 2010
Messages
2,046
Re: Just Got first boat; Shift Shaft Question

Lower-Unitsdriveshaft.jpgLower-Units0061.jpg
Here are 2 views of the guts of the LU - in pic 2 item 2 is the shift cam, in pic.1 item 44 is the shaft that rotates the cam.Any external pieces on the shaft are for the reverse lock, try turning the shaft CCW for a few degrees and see if it will stop and stay in place - now the prop should turn in neutral.
 

briaineo

Seaman
Joined
May 13, 2013
Messages
58
Re: Just Got first boat; Shift Shaft Question

What is your engine s/n?

Gerry

Hi Gerry

Serial number is 9034098

One quick question, should the cam be in neutral for forward on re-assembly? Have read post saying both
 

carholme

Rear Admiral
Joined
Sep 4, 2010
Messages
4,845
Re: Just Got first boat; Shift Shaft Question

Yes, the s/n confirms that it is a 1974 made in Belgium engine.

Parts List:

MERC 402 - Mercury, Mercruiser, Force, etc. Parts Lookup

Here is a link to the condensed version of the Clymer manual. Download it soonest to your computer as the link is short lived.

See the cam installation for your engine as Fig. Fig. M1O-38 on page 236 and the following from page 235:

Before attaching gearcase housing to
the drive shaft housing, make certain
that shift cam (7-Fig. MlO-36) and the
shift lever (on motor) are in forward
gear position on models with reverse
locking cam shown in Fig. MlO-37 and
neutral position on models with reverse
locking cam shown in Fig. MlO-38. Complete
assembly by reversing disassembly
procedure.


If the picture is too dark for you, let me know and I'll get a better one.

Gerry
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,687
Re: Just Got first boat; Shift Shaft Question

Hi Gerry

Serial number is 9034098

One quick question, should the cam be in neutral for forward on re-assembly? Have read post saying both

Both are used. Designer choice if you will. With the shifter and LU in F the prop is handy for a 1 man operation and you can grasp the prop while stabbing the LU while getting it to mesh.

I use the other, N as I like the solid detents on the control and in the engine. Yes I have to turn the crankshaft to get the mesh, but that's my choice.

Mark
 
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