Mercury KF3 gear case set up

[green-thumbs]

This is a gear case similar to KF5, KE4,Mark7 and KF7 in that shims between bearings (on prop
and drive shafts) and machined surfaces of case are used to set gear lash.

How do you know when you have it right and more importantly how to know which shims to add
or subtract to arrive there? I have parts and service manuals but they either say "assemble in reverse order" or duplicate original "feel" .
I am in frame of mind to do it but danged if I can figure out where I am going or how to get
there or even when I have arrived.
Thanks
Louis

There were several good reasons to take case apart…worn splines and broken skeg needed
welding.

[wiscoboater]

I believe you coat the gears with white grease, assemble, turn the shaft and then inspect the contact pattern in the grease, looking to get contact patches centered on the gear teeth. Shim up or down to change contact point. I could be wrong though so wait for a Merc guru to either agree or debunk that process.

[richardg]

Assemble the lower unit
Lift up on the drive shaft.
With the right amount of backlash there will be a little bit of back and forth movement and some clicking when you rotate the prop shaft clockwise and counter clockwise.

[green-thumbs]

Duh…
Louis

[foot_doctor]

The simple test that I prescribe is this: After assembly, lift up on the drive shaft and press in on the prop shaft while rotating the drive shaft in a clockwise direction. With some resistance applied to the prop shaft it should feel as though the coupling between the shafts was accomplished by a rubber hose. No clicking or bumping of any gear teeth should be felt. If the drive shaft is allowed to fall into the gear case, all of the teeth should be felt. It does not operate in that position, as the gears are driven apart by the energy transfer. Trial and error works. Have patience. There are typically no standard beginning shim standards, and if a different gear set or bearing set are employed from original, the original shims may not be appropriate.
R.T.

[green-thumbs]

Thank You
You explain the subject clearly.
Louis

[Author]

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