OMC LU ,identify year and Hp

[PugetSoundBoater]

I got this longshaft Lower unit today. It looks to be what i need to convert my ’81 Johnson to a longshaft. The splines on the top of the driveshaft has an o ring right below the top splines ,like on the early 9.9/15 . So i think i might have to swap the driveshaft with a later one,i recall i had a discussion with a member about the driveshaft o ring/seal issue. My current short shaft LU has a short stud that attaches to the mid section ,this uses a long bolt,which i have from a ’68 Johnson 20 hp, but think i will need a 6′ long stud with the longshaft LU.
If anyone could let me know if this will fit my ’81 25 hp that would be great. If better or closer photos are needed,let me know .
Thanks ,Jim PSB

"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson

[frankr]

Hoo boy, good question. You will have to change the drive shaft, for sure. The big question is if the ’81 shaft will fit that older gearcase assy. I don’t know. Along with the stud/bolt issue, you will need the long version of the tube that surrounds the drive shaft. Then, how about the shift rods and water tubes? So many problems. I started to look at the ’81 parts books but found 12 different Evinrude 25hp model numbers, plus the Johnson models.

[PugetSoundBoater]

My 1981 Johnson is model J25RCIM.
Frank,in regards to your comment on the drive shaft, you mean the number of splines on the top and bottom differ with the years? I have not removed the short shaft lower on my motor yet so i will have to do that first before doing any more parts hunting.
I kinda figured this may be a challenge to adapt ANY "looks the same" LU to mine .
I have looked at the ME parts diagrams over the last couple weeks and see that there are several issues to address. A real mind numbing list of succeeding parts #’s for the different needed parts.
I’m sure i will learn something.
Jim PSB

"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson

[fleetwin]

Yeah, there is also an issue about the driveshaft oring. Some models had the oring on the driveshaft, others had the oring in the crankshaft with no groove on the driveshaft. Does your original driveshaft have an oring groove? You will need a longer water tube, I’m pretty sure your water tube will just pull down out of the upper grommet. The shift rod in the long shaft gearcase should fit right into the brass connector. Your picture of the new gearcase shows a water tube, so hopefully that is the longer one that you can use in place of your short water tube.
Once you have checked/changed the gear lube and replaced the impeller (and found the right driveshaft), you will want to check the shift linkage and make sure it is adjusted properly. These gearcases are very sensitive to proper adjustment, and will start jumping out of gear if not properly set up/adjusted. Repairs can be very expensive.
Post more pictures if you still have questions…D

[frankr]

Upper D/S splines on your ’81 are different than the older 22 cubic inch 25’s. I don’t know about the lower end. The o-ring for the upper end is in the crankshaft rather than around the drive shaft. Like you say, mind numbing.

[PugetSoundBoater]

Fleetwin ,Frank, thanks for your input. I compared the 2 LU side by side ,the original short shaft still mounted on the motor, the shift rod height looks good on the Longshaft. As i recall in my repair manual,there is a procedure for adjusting the shifting which i’m sure it will need. More than put it in neutral and spin the prop ,listening for clicking. But that is a starting place.
When i get the short shaft LU off i will carefully measure the water tube length, shift rod height etc.
I will then probably have some more specific questions ,with photos.
Thanks,Jim PSB

"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson

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