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Merc 25XS Gearcase Service

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  • Merc 25XS Gearcase Service

    Hi all. I was checking out the gearcase for my 25 XS, and it needs some service. At very least seal replacement. Is there such thing as a service manual available for these? If not, who would be a good person to do the work for me? Preferably somewhat local.

  • #2
    Where is local located?


    • #3
      Lol. Should have mentioned that.. I'm in Ottawa, Ontario.


      • #4
        You received a PM to contact Foot Dr Ron Thomas Milwaulee Wi. @ 414 353 4465....

        Shipping Canada to US and back might be a cost issue, not sure what happens at customs each way?
        "Keep Move'n" life is catching up!
        No man's life, liberty or property are safe while the legislature is in session.


        • #5
          Yes. Shipping and customs can be a little prickly at best. I would normally drive to upstate New york for shipping and receiving, but....


          • #6
            Yes.... The Foot Doctor, Ron Thomas is the best, you can’t go wrong

            Dean F. Hobart


            • #7
              It's no trick to service inless your changing the casting then you have to reshim it. Just keep track of the shims and put them back where they came from, it's a misconception that you are shiming gears your shimming housings, gears and bearings are plus or minus .001 so if your gear lash is OK when you tear it down it will be fine after new bearings and seals. You might need a water pump housing puller.


              • #8
                Thanks for the barrage of replies. Laddies, I tend to agree with you. Without the lash specs though, I am afraid to assume they are good. There is a fair amount of axial play in the driveshaft which concerns me.
                Does the pump housing pull out or thread out?


                • ZUL8TR
                  ZUL8TR commented
                  Editing a comment
                  Before maybe sending off to Ron Thomas do a few external checks and inspection.

                  Axial up down play at drive shaft is normal provided it is not excessive? It is set by shims at the bottom of the drive shaft ball bearing and gear teeth mesh pattern. If nobody fooled with these shims from factory setting that is good, but unknown? This ball bearing also has shims on the top and below the pilot bushing to set the pilot flush with the top of the gear case, When gear case is mounted on the tower that keeps the pilot from moving up under load. When under power the drive shaft moves up when the prop gear is loaded.

                  To check gear lash remove gear case off the tower -  pull up on drive shaft and keep from any rotation and then gently slightly rotate prop shaft CW to CCW, there should be a very small feel between gear contact, that is lash and spec is about 0.004" I tell by feel, If excessive you will know.  Also with drive shaft pulled up and rotated there should be a very smooth operation of the gears meshing with prop shaft rotating, like a knife thru soft butter. If you do the same without pulling up on drive shaft there will be a noticeable feel of the gears meshing.   

                  There should be no lateral play of the prop shaft with the cone nut tightened. If there is the bearings are worn in the cone nut and inside the gear case. There are 4 seals on the prop shaft, 2 in the cone nut, 1 in the water pump housing and 1 O-ring outside the water pump, the drive shaft has 1 seal.

                  Also note the condition of the drive shaft at the pilot bushing seal, is the shaft surface free if any rust, etc. That area where the pilot sits ia a water trap will cause rust if not dumped after use. 

                  ​​​​​​​If in doubt on gear case service send it to Ron Thomas he is the expert. You can also call him to discuss in detail I have had several tele conversations and emails with Ron.

                  414-353-4465 Email birdfoot_23@yahoo.com

              • #9
                It pulls straight out, there is a dot in the face of it for alignment so check it for pulling. some pump housing can be pulled with out the puller by stacking spacers on top of the housing and using the prop nut to pull it lose but you can only move it the distance that is available between the end of the water pump housing and the end of the gear case. then hopefully if will just pull out. If you want and I can get my kids to get it for me I could either send or post the repair of a 55H they are all the same basically.


                • #10
                  Thanks to all the great help, I finally have my gearcase sorted out. As it turns out it is a good thing I took it apart. It didn't register right away, but when the prop shaft came out, the front needle bearing was on the shaft! It wasn't even pressed into its seat! No wonder it didn't feel(or sound) very good. It would not have lasted long in that condition.
                  Steve Roskowski coached me through the particulars of rebuilding these units. As it turns out the original bearings are not a standard item and are no longer available. Found this out the hard way... Squeezed a new bearing in to the front of the gearcase, only to find out the shaft would not slide in. WTF? The original is .747" dia. The new one is .752" Ugh! I had to mull that problem over for a few days.. Fortunately, I was able to fab a button puller to get that bearing out.

                  Now some machining needed to be done. The bearing seats all had to be reamed out to .750" to acomodate the new bearings. This required the fabrication of some jigs. Being a machinist with access to all the tools required has its benefits.
                  All said and done, the new bearings were pressed in, new seals installed and the test assembly went perfectly! everything turns smoothly, with just a hair of backlash. This was definitely a challenge!
                  As for final assembly(this evening), what gear lube is recommended for these units? Do I pack the cone bearings with Lubriplate 105?
                  Thanks again for a the wisdom passed on. I wouldn't have succeeded without it.
                  I'll upload some pics later, they need to be resized.
                  Have a great day!


                  • #11
                    Some use grease in the gear case I prefer gear oil over many years of use .

                    Tried many brands and types and settled on 75w-90 Royal Purple full synthetic in my 25ss quicki gear case because it is good for GL4 (and GL5) rating with low corrosivity compared to lubes with just a GL5 rating. You can also use Mercury Hi Performance gear lube 90w also good stuff but hi vis. With seal riding surfaces in great shape, the seals and bearings are good I do not get water in. All these years only replaced seals in the 25ss quicki Should work in the 25xs.

                    For the outer cone I have tried many greases and determined that the standard NGLI #2 is too thick and makes the rollers slide a lot rather than roll. Tried Luber-105 and it is OK but need constant refreshing when daily using the engine. The best I found so far is John Deere Corn Head grease, available at farm supply stores, it has unique properties not rotating and rotating and is NGLI#0 and the rollers roll. When running engine all day long it stays in the cone bearings. As a matter of good PM after each use I re-grease these outer cone bearings and as well as replace the gear oil, lube is cheap parts are expensive.

                    The 25ss takes a drawn cup precision ground GB98 prop shaft roller bearing in the gear case front end as well as 2 in the outer cone. Does your 25xs take a GB98 if so did you get a GB 98 (not a G must be GB) prop shaft roller bearing? They are still available. I am surprised that you had to ream out the case for the bearing to fit, if it was a G98 that would explain it?

                    Maybe the 25xs used a different roller in the case front for the prop shaft compared to the 25ss GB98?

                    GB98 price example

                    "Keep Move'n" life is catching up!
                    No man's life, liberty or property are safe while the legislature is in session.


                    • #12
                      I did have to ream the seats in the gearcase and cone out to .750" to accept the GB98 (or SCE98) bearings. Not sure what the original bearing was. They had no stampings to identify. The bearing supply house could not cross reference them with the given dimensions. Weird! At any rate, GB98's it is from here on in!
                      Picked up some Royal Purple yesterday, will try to source some JD Corn grease today. WooHoo!


                      • ZUL8TR
                        ZUL8TR commented
                        Editing a comment
                        Corn head comes in caulk gun tubes. I lean out the old grease in paint thinner dry and caulk gun the CH in the cone and pinky finger it well into the GB98's at each end and pack a lot in there also at seal backs, prop shaft pushes out excess. I also have a special made brass grease tool (circa 1973) that fits over the prop shaft and pushed against the outer seal and it has a zerk fitting to pump in grease. To accept the sharp edge of the grease tool I put installed the outer seal lip facing inward, no water issues when grease packed well. I used this tool during the race days so I could get a quick shot in there without cone removal. When putting engine away until next use I would clean all the grease out and do the regrease as noted first above and also drain and refill the gear oil.

                        When I put up the engine after regreasing the cone and changing gear lube I use NGLI#2 heavy grease with molydisulfide on the cone threads and screw it in hand tight and leave it that way until ready to use. I torque the 25ss at 80 ft lbs never loosened underway ever. I sharpie pen a note on the case to torque the cone nut when ready to use. This onloads the cone threads and adds life, still have the same 1973 25ss cone.

                        JDeere CH grease, Canada from US shipping could be an issue? If CH grease becomes hard to get just use the 105 and do it as described above with fingering in the grease well.

                        Other suppliers are way out on cost compared to this place?