OMC Gearcase assembly swap?

[outbdnut2]

I’m looking at swapping a gearcase assembly from a 1959  35 HP Lark (same as Johnson RD-21)  to a 1965  40 HP Johnson RD-27.   Neither has electric shift.  Both have the Super Quiet lower.

According to the 1974 Johnson Parts Reference (swap) Guide page 19,   if I am interpreting it right,  it says RD-20 through RD-30  gearcase assemblies will swap, “Except for driveshaft”.

So just asking as a sanity check  – does this mean I can make the swap if I keep the RD-27’s original driveshaft, and put it in the 1959 35’s gearcase assembly?  I’m trying to avoid the work of putting a seal kit in the existing RD-27 gearcase where the propshaft seal is leaking big time.

The impeller is the same part number for both motors.

Thanks,

Dave

 

[Waunnaboat]

I don’t know anything about these motors, but if the LU gearcase assemblies are the same, I would think that there is a difference in length or method of attaching to the power head between the lark and the Johnson.  Could you mabey just swap the gearcase and keep the driveshaft on the lark?

"Outboards seem to multiply exponentially..........I find that for every finished project, there are two more waiting to be completed."

[fleetwin]

Hmmm, very interesting.  Never thought about it but are the driveshafts the same for the super quiet models vs the conventional exhaust housing models?  I suppose I could look this up myself and see!

[fleetwin]

fleetwin wrote:

Hmmm, very interesting.  Never thought about it but are the driveshafts the same for the super quiet models vs the conventional exhaust housing models?  I suppose I could look this up myself and see!

OK, reread your post, you are working with two super quiet gearcases.  Seems to show different numbers from  59 vs 1965, doesn’t show supercession either.  I don’t suppose you have the two gearcases in front of you so you could place the driveshafts side by side to compare.

Miss you Frank….

[Crowsbeak]

Perhaps the difference must be in the driveshaft splines either number or length on the powerhead side then?

1954 Evinrude 7.5 HP
1954 Evinrude 15 HP
1954 Gale 12 HP
1955 Johnson 10 HP
1956 Johnson 10 HP
1956 Gale 12 HP
1956 Evinrude 5.5 HP
1958 Johnson 7.5
1960 Evinrude 18 HP
1973 Johnson 6 HP

[outbdnut2]

I’ll get to having them side by side in a week or so.  Page 19 of the 1974 parts  manual seems to say RD-20 thru 30 gearcase assemblies will swap between each other if you keep the driveshaft with the motor it came with.   I will have to swap shift rods , as I’ll be going from short to long.

I’ll report back when I get the gearcase assemblies and driveshafts side by side.

Dave

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