Re: 1974 115hp - Replacing the reverse gear or bearing..
I have a manual for a current design lower unit which is very similar so I am going to work back and forth (memory of old to info in the manual).
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First thing to do is shift to F gear. This should get your shifting fork out of the way for when you pull things out later.
You probably will do better with the lower unit attached to the engine and the engine tilted up so that you can work after you drain out the fluid.
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I too think cutting it out is the best bet. You don't have to worry if you nick the housing as the seal is down the side of the insert, not on the face of it, or under the nut.
I'd dremel it in a couple of places (like maybe 1/6 of the way around it (circumference of the nut)and with a small pick or screwdriver, pick, tap, drive that piece out then go after the rest. Should come out easily.
There will be corrosion between the insert and the inside wall of the housing; so more liberal application of penetrating oil.
I don' remember if the insert has a lip that the fingers of a puller can grasp or not. I think not. So, the problem is grasping the insert with enough bite to stay put while you drive it out. A slammer hammer works best if you can figure out how to grasp the insert. (It's been about 25 years since I did the last one and I just forgot how I got mine out.)
Just had an idea. A pair of vise grip pliers clamped to two of the supports (of the insert) with a bolt stuck between them would give you a bar which you could hook your slammer around and bring her out. That might work.
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Manual says that the shaft is clear to come out with the insert when it comes off, or pull it off then pull the shaft out (clutch dog is pinned to the shaft and comes out with it).
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On the front end of the prop shaft (inserted into it) is a spring, a spring adapter, some ball bearings (3 on current models), and a centering pin that the balls go into and the spring adapts to. Be sure you get them back upon reassy. Also, if you are removing the clutch dog locking pin so as to get it off, you have to push on this pin to relieve the pressure on the dog locking pin.........but don't turn it loose as the spring and all will come flying out once the pin is out.
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The gear teeth (that contact the drive shaft gear) may be pitted on the mating surface, teeth missing, or inside of it the slots that the "clutch dog" fits into worn out (rounded edges of the slot) are potential prolems to check. Then there is a thrust bearing that the R gear rides on with a thrust washer on the other side to inspect.
Course the clutch dog could be bad or both. I would replace the clutch dog while in there if any sign of rounding of the corners on the front or rear, chipped teeth or anything indicating damage.
Additionally is a roller bearing behind the prop shaft seal that needs to be inspected.
As I recall once the retainer is out (with the rev gear and bearing as part of it), the prop shaft, clutch dog, spring and ball bearings are free to come out too. Don't remember the interface between the shift fork and cutch dog but once you're in there you can probably figure it out....remembering the shift shaft twists and moves the dog back and forth on the prop shaft to do the shifting.
If you don't remove the F gear there is no shimming indicated in the manual so you can replace worn parts and put them back as they came out. All rolling surfaces should be thoroughly lubed with lower unit lube prior to installation.
I'd put the prop on and rotate it thru the gears while turning the propshaft to insure that everything is nice and smooth prior to reinstalling oil. Don't forget to refill the unit!
This is wordy and a manual would help, but when I did it I did it without one.
Good luck,
Mark
