Well, don't force it. If there is any pressure against the crank it will push the crank forward and ruin the rear main thrust bearing and destory your motor.
I while back I was told that the old style input shaft would not fit into a long hub coupler. So it is something to check. I would remove the shaft that goes into the coupler and try sliding it in by itself. That would eliminate that issue.
Is your XR the old style ujoint (with grease zerks) or the new one (without zerks)?
The new ones are more difficult to take apart but it is doable.
Are you rotating the propshaft to get the splines to line up?

Something is not quite right. It should slip on most of the way with little force. How are you supporting the drive when you are wrestling it on?? I made a frame that sits in my floor jack, that helps a lot..
Any pics?? That may show us something you maybe missing??

Dick

I found that since I didn't use the factory merc coupler bolts with the shoulder on them, the coupler wasn't being index correctly. I struggled to get my B3 to engage with the long snout coupler even though the alignment tool went in fine. My B1 didn't slide in super easy but it went in with a little push. I think the long snouts are more sensitive to the exact center of the coupler to the flywheel. I installed my non snouted coupler on it and didn't tought the mounts, the input slipped right in. I stubbled across the bolt sholder thing when pulling it apart. Even though I was confident the shaft would slide in to the long snout after using the proper bolts, I used the non snout.

I set up 2 - 2X4s that create a level runway to slide the drive on. Also use a bottle jack on the transom end of the set up to make small adjustments. Will use the trailer neck to make sure everything lines up correctly too. Used to wrestle with drives but became wiser in my old age.

Dick, I hope I didn't do any damage to the thrust bearing b/c I did put some force - not with a hammer thankfully - to the back of the drive to attempt to get it on. I am in the same situation as ACrook described above. Tool fits in fine but drive won't go on the last inch. With only an inch to go splines are definitely aligned.

Alignment requires coupler, bearing and centerline of the helmet to be centered around the same axis. Alignment tool only aligns bearing and coupler. My next step is to break out the hoist and look at engine alignment to bring all three items onto the same axis.

Sorry for the delay in response, been on the dyno and no time to check internet..

Pushing on the drive while installing it won't hurt the motor. The guys that I have heard of hurting the motor was after the drive was about 1/4" - 1/8" from mating.. they would use the bolts to get it on the rest of the way.. Then go out and run (ruin) the motor in a short amount of time. The crank is pushed forward due to the mismatch of input shaft and the long coupler snout. I was told, input shaft with one onring is old style and would not fit in a long snout coupler.
Last time I mentioned this, one reply was that the above situtation was not true when he attempted it. So maybe, Merc fixed the problem.
But like you say, something is not right with yours.. 1" should have the splines aligned.

If you must, you could take the front shaft off the ujoint assy and see if you can slide it into the coupler through the transom assy.. That would tell you the match is good, and eliminate the bellhousing/drive variable.
Good luck with it. You will find it, and it will be something simple?? Always seems to work that way..

Dick

Dick, I am pretty sure I am replacing like with like. Coupler was the same when side by side. So were the yokes on the drives. Old yoke separated just above the splines then spun around in the coupler grinding to point almost like a pencil - no exaggeration.

If I push down on the back end of the tool, I can almost get it to start into the splines. Definitely not right so don't want to force it. Gimbal bearing looks to be square in the housing. Even if the gimbal bearing was off square a little or too far in the housing, isn't there enough play in it to compensate for a small amount of misalignment?

My only idea is that bolt holes in the front mounts may have elongated over time and allowed the engine to drop slightly. Since the snout of the coupler is behind the mounting bolts, a drop in the front of the engine would raise the end of the coupler.

Thoughts?

Thanks.

My U joints always hung up on the bellows collar just a hair, had to get western with it then poof slides right in