How do you change a prop shaft on a 1991 25 HP Merc?

[Bob A]

Do I need to use a pulling or turn carrier tool?
Do I need to pull the lower unit?

Any help would be appreciated.

Thanks,

B

 

[galamb]

You would do well to minimally invest in at least a Seloc's manual.

You can remove the propshaft with the lower unit attached.

It helps if you use the bearing carrier removal tool from Merc but it's not absolutely necessary.

First step is to drain the lower unit (or you will have a gear oil mess when you get the bearing carrier out).

Then remove the prop and any thrust washers etc.

Next, remove the three screws that secure the o-ring retainer (around the bearing carrier).

Then you can remove the bearing carrier. It is "screwed in" with a LEFT HAND THREAD so you have to turn it clockwise to undo it.

If you are going to have an issue, this is usually where it occurs. The bearing carrier gets "corroded" into the lower unit. You need to be careful - these parts are aluminum and whacking/reefing can result in a crack requiring replacement or significant repair (read $$$$).

The tool from Merc is kinda like a slotted socket that meshes with the (teeth? ridges?) on the bearing carrier - you can jury rig something that will work if the carrier is not seized badly in the threads. If it is, heat, penetrating oil and prayers sometimes help (followed by yelling at it to scare it into submission )

If you do get the carrier to move the prop shaft and reverse gear will come out with it along with the clutch dog.

The cam follower and spring (that moves the clutch) will often launch out of the end of the prop shaft (forward end) - unless you are going to replace them, don't lose them - they are (small) and could easily get lost if you are trying to work in the back yard or driveway.

You didn't say why you are pulling the shaft - is it bent? (replacing it). In any event I would minimally replace the o-ring seal and the shaft seals if they are suspect at all (you have it tore down and they aren't that expensive).

The forward, reverse and pinion gear are a matched set - you shouldn't replace only one or the others will die a premature death (again, don't know why you are pulling the shaft).

If any of this sounds unclear or confusing, see my first suggestion (about the manual).

DO NOT touch the pinion gear unless you have the capabilities to torque it back to "exact" spec - if not re-installed correctly you WILL chew up your gears in short order. The forward gear can be "worried out" under the pinion after the prop shaft is pulled (if that's where you need to get to)