Rebuilding a lower unit?

Anyone ever pull their own lower unit apart? How tough of a job is it?

I've got a 2000 25 Yamaha that I think the gear shift clutch needs replacing. It won't go into reverse no matter how I adjust the linkage.

Tends to require more specialized tools that all but the most invasive of repairs on the power head. No experience first hand, but reading the factory service manual for my motor I see all sorts of pullers & what not required for cracking open the lower unit.

You can do it without a puller, but you have to be careful not to bust the lugs where the bolts go through. If you do, then you have to replace that carrier housing.

First thing to do is to drain the lower unit lube, unless you want it everywhere when you pull the unit apart. Set down cardboard anyway, as it's still going to be messy.

After removing the 2 bolts on either side of the prop shaft, use a block of wood and a hammer, and CAREFULLY tap the lug sideways, so as to rotate the carrier housing. Alternate between bottom and top lugs. Once you have it rotated so that the lugs are sideways, once again, VERY CAREFULLY tap on them from the forward side, using a dead blow hammer. This is the part where you have to be careful, or you will break those lugs. Once again, alternate between them, so that you are not causing the carrier housing to be canted as you're trying to remove it.

When the carrier assembly comes out, the prop shaft will also come out with it.

Installation of the carrier during re-assembly is fairly simple. Use a block of wood, drive it back down flush, with the lugs closely aligned. Use the wood block and tap the lugs sideways to align them with bolt holes.

Straight from a VERY new novice - I have always been intimidated
of opening up the lower unit. I would always take it to the shop.
This past week, I did my very first ever gear case overhaul and I
could not believe how quick and easy it was.
The first thing to do is dedicate two weeks just for this project.
This will allow you ample time to remove, disassemble and clean everything.
Then, order all the parts that you think should be replaced.
Putting it all back together is a snap - an hour at the most.
But - I was working on a 1960 and 1966 Johnson 2-Stroke. Not a 2000 Yamaha

Check your model here and you can get an idea of what it entails.
https://www.marineengine.com/parts/yamaha-outboard-parts/2000/25/F25ELRY/620300170028

Yep what PSG said cept i used a piece of brass

"you can do it without a puller, but you have to be careful...use a block of wood and a hammer...CAREFULLY...VERY CAREFULLY"

I'm sure with experience you absolutely can do many things with a block of wood and a hammer...question is should you?

It's always easier to do a job if you have the right tool. But sometimes you don't and you have to improvise. Or every once in a while, you make your own tooling, as I have done for various tasks involving my jet boat.

That said, like Johnny, until last year, I was a complete novice at opening up a lower unit, the thought of it always intimidated me. Until the day I hit an underwater object and snapped my driveshaft. And they wanted 600 dollars for a new driveshaft, not to mention the labor to change out all the parts. I disassembled my lower unit, welded the shaft back together, and put it all back together. Ran another year until I hit another underwater object and did exactly the same thing #-o Except this time when I disassembled it, I busted the ears off the carrier housing and had to get a new one. :x

In any case, once again, took it apart and fixed it. Running like a champ.

The answer to that question is ..... "It depends"
On what needs to be done inside the gearcase.
If no driveshaft or gearset needs to be replaced then the number of special tools is greatly reduced.
If they do need to be replaced then shim tools are required and they are costly. Yamaha gearcases are usually more special tool happy than OMC.
We have a Yamaha 40C gearcase in the fixture at the shop right now. Will not shift out of forward gear. While evaluating I noticed the driveshaft is out of round at the driveshaft seal area. This alone put the estimate on repairs out of reach of the customer. The cost of special tools for us to do the job correctly put the job out of reach for us as well.

My 09 mercury 20hp was not bad at all. I was surprised and how simple they were. Mine grenaded the bearing and in turn ate one of the gears. Pulled it all out fairly quickly and painless. Went back together easily.