Gear Ratio: '73 65HP vs. '77 75HP Evinrude?

[Mas]

Hi,

My motor is a hybrid of a 1977 75 HP Evinrude powerhead sitting atop a 1973 65HP Johnson leg. Obviously a previous owner did some changing. My question is "what is the difference in gear ratios between the two motors? Are they exactly the same? Also, how can I determine the gear ratio without breaking down the gear case?

Thank you,

Mas

 

[racerone]

No difference in gear ratio.------Turn the flywheel 10 times and count the # of turns of the propshaft.-------Does the 77 powerhead have the proper bits on it to shift the 73 lower unit ????----Picture of starboard side of the motor required.

 

[Mas]

I'm not sure what is original or mix-matched concerning the shifting hardware. It could be only the mid-section was replaced and not the LU??? I turned the flywheel ten times and counted 4 1/8 prop revolutions...does that seem correct?



Thanks,

Mas

 

[racerone]

Does it shift to forward properly ?

 

[Chinewalker]

Someone has modified it. The flat stock connector between the arm the shift cable is attached to and the shift lever is home-brew. Before launching boat, check the rotations for proper shifting. Shift the control box lever into forward, rotate the flywheel CLOCKWISE by hand and note which direction the propeller rotates. If propeller turns clockwise (when viewed from aft), you're good.

 

[Mas]

I have not had the motor on the water yet. But, when testing for gear ratio, the gear case shifted into forward without issue. Also, I've done some researching to learn about "big vs. small" gear cases...which do I have? How do I tell?

Mas

 

[racerone]

It is not a 73 gearcase.

 

[Mas]

The only reason I even realized there might be some mix matching is the ID tag on the transom is 65ES-73R, which does not match the plug on the power head 75743S. Maybe possibly, only the transom clamp/swivel bracket with the ID tag was swapped?? I certainly do not have any experience with this size motor.