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1971 7.5hp model 217-58820 with wrong lower unit and shaft length

I have a 1971 Eska/Sears model 217-58820 that I am trying to restore. It was a trade in I got while working on a friends motor. It seems that the wrong sized lower unit driveshaft was installed. I removed the lower unit after there was no movement when the shift lever was engaged and the flywheel/motor was turned. After removal I found the lower unit was working properly when turning the shaft or the prop. I inserted another lower unit with a 22" shaft and found that the flywheel and lower unit engaged but the shaft was too long. The driveshaft on the lower unit I took off is approximately 19 5/8 in. It looks like a lower unit from a different model was put on the motor. I then pulled the engine block off and inserted the original lower unit into the clutch assembly and pushed it all the way in and the driveshaft engaged and turned like it should. Looks like a shaft that was 20" would be what I need. Was there a difference in shaft length for different years or models??? Any suggestions on how to resolve this problem would be appreciated. I can modify if I have to.
 
I have a 1971 Eska/Sears model 217-58820 that I am trying to restore. It was a trade in I got while working on a friends motor. It seems that the wrong sized lower unit driveshaft was installed. I removed the lower unit after there was no movement when the shift lever was engaged and the flywheel/motor was turned. After removal I found the lower unit was working properly when turning the shaft or the prop. I inserted another lower unit with a 22" shaft and found that the flywheel and lower unit engaged but the shaft was too long. The driveshaft on the lower unit I took off is approximately 19 5/8 in. It looks like a lower unit from a different model was put on the motor. I then pulled the engine block off and inserted the original lower unit into the clutch assembly and pushed it all the way in and the driveshaft engaged and turned like it should. Looks like a shaft that was 20" would be what I need. Was there a difference in shaft length for different years or models??? Any suggestions on how to resolve this problem would be appreciated. I can modify if I have to.

Well I solved the problem. I had another lower unit stashed behind my restored outboards that I had forgotten about off of a 217.58531 Ted Williams. i installed it and found that the drive shaft was binding when I went to tighten up the bolts. The flywheel would not turn unless I loosened the 2 bolts holding up the lower unit. After removal and inspection I found that there is quite a variation in the way different manufacturers of the drive shafts machined the splines. (Clinton , Eska,etc) In the attached pictures you can see the spline length variations go from 3/4, to 1, to 1 3/16". In order to make the unit work I took a dremel and grinding wheel to lengthen the spline indentation on the shaft from 3/4" to 1 1/4". I then installed the modified lower unit and tightened the bolts and she is working the way she should. Any idea how to install the v spring on the shifter would be greatly appreciated.
 
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