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Lower Unit trouble re-install

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RickR90s

Contributing Member
I have a 2019 Mercury 60hp Command Thrust OB on a pontoon.

I figured it was about time to change the impeller so I dropped the lower unit. Installed the new impeller with no issues and now I can't get the lower unit in place. It appears that the shift shaft is no aligning, but no matter what I do, (visually align the splines, rock the shift lever back and forth while I try to seat the unit), the closest I can get is about a 1/4" gap. And if I try and use the bolts to pull it tight, it immediately binds and the shift lever won't move (which appears to indicate the shift shaft splines are not aligned).

There is really no room to see in there, so wondering what tips you pros might have.

Thanks very much,

Rick
 
Hi Rick, I had a similar problem with mine a few weeks back. Not the same motor, but like you I was not able to get the lower unit reattached and had about a half inch gap. I gave my mind a day's break and worked on other stuff. Just sitting in my truck staring at the damn engine on a stand and I noticed the gear select linkage that moves up/down with the shift rod to prevent the shaft from bucking out of the water in reverse..well yeah, I was looking at the hole in the cowling when it dawned on me, that damn shift rod! I never passed it through the hole! And yes it's an extremely unnerving process by yourself, but it all came together nicely after the rod was in place...AND I won't have to worry about hell wreaking havoc in reverse anymore, since I was able to FINALLY properly set the rod position. It worked it's way out of alignment a few years ago and I hadn't figured out how to properly set the position, and just exercised extreme caution while in reverse, but when I needed it bad, I was screwed - happened a few times - freaks people out, but never again.

Also, rotate the drive shaft by hand clockwise using the propeller to assist with alignment, and/or the cam shaft by gently pulling the starter rope or rotating the flywheel.

Mike
 
Morning Mike, I'm at a loss as I've been working on boats, motorcycles, cars my whole life. And probably replaced at least 10 impellers on other outboards over the years. Never had a problem. I do know now that it was recommended that I place the the control in Forward before removing. The boat is a 2019 Crest I.

Instead, I left it in neutral and pulled the LU. Replaced the impeller, but like I said, can only get the unit in to about 1/4" gap and don't want to use the bolts to seat it up as that doesn't feel right.

Here's what I've done:

Tried placing the shifter on the LU in Forward, Neutral, Reverse and match that to the lever on the boat.
Tried having my wife move the lever slightly while inserting in each of those three positions.
Rotate the flywheel while inserting. (I think the main shaft is engaging as I can rotate the prop and see the flywheel move)
Try and position/center the shift shaft in the motor housing to align with the shift stub on the LU
Grease everything, all male and female components

This is definitely a dilemma.......
 
The shifter HAS TO be in Forward when doing this on a Mercury that has a 'foot' on the shift shafts. If you know that'sin Forward, it means that the lower shaft can be matched to it, so it won't go into neutral or reverse when shifted to one of the other gears. If the upper goes far enough to use the nuts to pull it together, this is the only reason- one of the 'feet' is resting on the other and trying to push it down, which won't work and it will cause damage if forced. If you separate them and can no longer get the lower into any gear by rotating the shift shaft, it likely means the crank shift may have broken and if it does shift into all gears, it means the upper shaft may have been forced upward hard enough to shear the pin holding it into the lever that's turned by the end of the cable.
 
Success. I went to my local boat dealer and he explained that the last 1/4" of gap is enough to install the bolts and cinch it up. Apparently the two locating pins are tight enough that it won't mate flush to the engine housing.

Thanks everyone!
 
Yeah reading what Jimn said and from what You've reported it's definitely shift shaft/lever related. It sounds identical to mine, however, yours might be more difficult to realize having what I'm assuming is a remote shift lever attached to cable. Also, I too could rotate my prop and engage the flywheel, but couldn't close that small gap until I passed the upper portion of the shift shaft through the small hole (1/8") in the cowling where it contacts the 'foot' lever for maintaining a lock on the pivot while operating in reverse.
It would be a massive coincidence if our identical situations proved to not be related. I'm confident there is a similar solution for your dilemma and you're gonna find it.
Mike
RickR90s said:
Success. I went to my local boat dealer and he explained that the last 1/4" of gap is enough to install the bolts and cinch it up. Apparently the two locating pins are tight enough that it won't mate flush to the engine housing.

Thanks everyone!
Click to expand...
Excellent news Rick! Good to hear you got her fixed!
 
I'm back. So my wife and I launched the boat yesterday. Foolishness on my part for not checking if the lever at the helm would go into forward or reverse, but its stuck in neutral. I did start it up in the driveway to verify the impeller was squirting water, but never felt comfortable checking forward and reverse with a spinning prop.
So we launch the boat and she goes floating off with the engine running normally. And then she says, "Hey, this GD thing won't go into reverse!". I thought she was joking but nope, it won't and the wind is taking her around the point. Luckily, she grabs an oar and somehow paddles close to shore where I wade in and grab her. We then got it towed over to my dock as I didn't want to put it back on my neighbor's jury rigged trailer. :)

So now, I'm trying to get a mobile mechanic to come out so we can assess. :unsure:
 
RickR90s said:
I'm back. So my wife and I launched the boat yesterday. Foolishness on my part for not checking if the lever at the helm would go into forward or reverse, but its stuck in neutral. I did start it up in the driveway to verify the impeller was squirting water, but never felt comfortable checking forward and reverse with a spinning prop.
So we launch the boat and she goes floating off with the engine running normally. And then she says, "Hey, this GD thing won't go into reverse!". I thought she was joking but nope, it won't and the wind is taking her around the point. Luckily, she grabs an oar and somehow paddles close to shore where I wade in and grab her. We then got it towed over to my dock as I didn't want to put it back on my neighbor's jury rigged trailer. :)

So now, I'm trying to get a mobile mechanic to come out so we can assess. :unsure:
Click to expand...

I'm not trying to beat you up but why didn't you check it out on the trailer?

The shifter was in neutral when you reassembled it? I posted previously that it HAS TO be in forward. Mercruiser sells a tool for holding the propshaft in place while the lower is being installed- if the lower is shifted into forward or reverse and the propshaft rotates, it won't stay in gear, so the propshaft needs to be held against the clutch dog by trying to rotate it in reverse. This is the same as the force that resists the prop's rotation when it's in water.

I'm using GC to mean 'gearcase'.

The upper shift shaft is in the gimbal housing and when the whole drive is reinstalled, the foot on the lower shift shaft and upper need to fit together and can't be forced. However, when the lower gear case is removed by itself, all you'll see is the splined shaft because the foot is mounted in the upper gearcase. This means that when setting up the lower GC to reinstall it, you need to turn the splined shaft to line up with the shift shaft by turning it in the direction that puts the lower GC in forward gear. This is a PITA but it has to be done correctly and it is possible, as you found out, to mate the two if the lower is in neutral or reverse. The upper shaft has a limit to how far it can rotate, the lower has three positions and the shaft doesn't click when it goes into any of them- IMO, they should have made that happen because it would save EVERYONE a lot of time and frustration.

You need to haul the boat out, regardless of which trailer is used. This isn't something you want to attempt in the water.

The .pdf of the Gimbal housing shows the shift shafts at the bottom of the diagram (Parts 19 and 20), the second shows the lower GC with the shift shaft at the right- this is the part with the spline and if you rotate it manually, you'll find that you can only rotate the prop in the 'forward' direction but it will click- this happens when the drive is shifted into Reverse. The next shaft position is Neutral and the prop should rotate smoothly in both directions and in the last position, the prop will only rotate in the reverse direction, which means the GC is shifted into Forward.

I'm also including the diagram for the lower GC, showing the propshaft and shifting mechanism. When you look at the middle group of parts that include the propshaft, you'll see Part #53- this is the shift lever and the splined shift shaft fits into it- if you didn't disassemble this, all you'll need to do is make sure the lower GC is in Forward gear when the shifter is in the Forward position and when you look at the foot, it's aimed toward the bow of the boat.

Note!
The shift cable rotates the upper shift shaft which receives the lower shift shaft and if that was causing the difficulty when you tried to reassemble it, the upper shift shaft (Part #19) may have been forced upward in its bushing and that will need to be corrected. I think this happened when I reassembled mine and I found that the upper/lower shafts don't always mate because the upper can move upward- I haven't removed the lower GC to verify this yet because I need to move the boat out from the back of my garage to be able to go behind it and work on it, but I plan to do this in before the weekend.

My own boat has a shifting problem-
My boat would shift into Forward, but had difficulty going into Reverse and after I raised the drive to go home, I felt that the foot and upper shaft weren't mating, so I left it for later. I'll report on what I find.
 

Attachments

  • BELL HOUSING (1).pdf
    165.5 KB · Views: 5
  • GEAR HOUSING (DRIVESHAFT) - MR.pdf
    182.5 KB · Views: 3
  • GEAR HOUSING (PROPELLER SHAFT) - MR.pdf
    182.1 KB · Views: 2
I'm not trying to beat you up but why didn't you check it out on the trailer?
My mistake. I own it.

The shifter was in neutral when you reassembled it? Both the helm shifter and lower unit were in nuetral when assembled. The dealer mechanic requested that both be in neutral so that's what we did.

I posted previously that it HAS TO be in forward. Mercruiser sells a tool for holding the propshaft in place while the lower is being installed- if the lower is shifted into forward or reverse and the propshaft rotates, it won't stay in gear, so the propshaft needs to be held against the clutch dog by trying to rotate it in reverse. This is the same as the force that resists the prop's rotation when it's in water.

I'm using GC to mean 'gearcase'.

The upper shift shaft is in the gimbal housing and when the whole drive is reinstalled, the foot on the lower shift shaft and upper need to fit together and can't be forced. However, when the lower gear case is removed by itself, all you'll see is the splined shaft because the foot is mounted in the upper gearcase. This means that when setting up the lower GC to reinstall it, you need to turn the splined shaft to line up with the shift shaft by turning it in the direction that puts the lower GC in forward gear. This is a PITA but it has to be done correctly and it is possible, as you found out, to mate the two if the lower is in neutral or reverse. The upper shaft has a limit to how far it can rotate, the lower has three positions and the shaft doesn't click when it goes into any of them- IMO, they should have made that happen because it would save EVERYONE a lot of time and frustration. Understood. So would it be advisable to:
Remove the lower unit
Rotate the lower unit shift shaft to forward
Have a helper move the helm lever to the forward position while installing the lower unit

You need to haul the boat out, regardless of which trailer is used. This isn't something you want to attempt in the water. Agreed

The .pdf of the Gimbal housing shows the shift shafts at the bottom of the diagram (Parts 19 and 20), the second shows the lower GC with the shift shaft at the right- this is the part with the spline and if you rotate it manually, you'll find that you can only rotate the prop in the 'forward' direction but it will click- this happens when the drive is shifted into Reverse. The next shaft position is Neutral and the prop should rotate smoothly in both directions and in the last position, the prop will only rotate in the reverse direction, which means the GC is shifted into Forward.

I'm also including the diagram for the lower GC, showing the propshaft and shifting mechanism. When you look at the middle group of parts that include the propshaft, you'll see Part #53- this is the shift lever and the splined shift shaft fits into it- if you didn't disassemble this, all you'll need to do is make sure the lower GC is in Forward gear when the shifter is in the Forward position and when you look at the foot, it's aimed toward the bow of the boat.

Note!
The shift cable rotates the upper shift shaft which receives the lower shift shaft and if that was causing the difficulty when you tried to reassemble it, the upper shift shaft (Part #19) may have been forced upward in its bushing and that will need to be corrected. I think this happened when I reassembled mine and I found that the upper/lower shafts don't always mate because the upper can move upward- I haven't removed the lower GC to verify this yet because I need to move the boat out from the back of my garage to be able to go behind it and work on it, but I plan to do this in before the weekend.

My own boat has a shifting problem-
My boat would shift into Forward, but had difficulty going into Reverse and after I raised the drive to go home, I felt that the foot and upper shaft weren't mating, so I left it for later. I'll report on what I find.
 
RickR90s said:
I'm not trying to beat you up but why didn't you check it out on the trailer?
My mistake. I own it.

The shifter was in neutral when you reassembled it? Both the helm shifter and lower unit were in nuetral when assembled. The dealer mechanic requested that both be in neutral so that's what we did.

The upper shift shaft is in the gimbal housing and when the whole drive is reinstalled, the foot on the lower shift shaft and upper need to fit together and can't be forced. However, when the lower gear case is removed by itself, all you'll see is the splined shaft because the foot is mounted in the upper gearcase. This means that when setting up the lower GC to reinstall it, you need to turn the splined shaft to line up with the shift shaft by turning it in the direction that puts the lower GC in forward gear. This is a PITA but it has to be done correctly and it is possible, as you found out, to mate the two if the lower is in neutral or reverse. The upper shaft has a limit to how far it can rotate, the lower has three positions and the shaft doesn't click when it goes into any of them- IMO, they should have made that happen because it would save EVERYONE a lot of time and frustration. Understood. So would it be advisable to:
Remove the lower unit
Rotate the lower unit shift shaft to forward
Have a helper move the helm lever to the forward position while installing the lower unit

You need to haul the boat out, regardless of which trailer is used. This isn't something you want to attempt in the water. Agreed
Click to expand...
Well, crap. I confused this thread with another one regarding reinstalling a lower GC, so the diagrams mean squat- I'm sorry for wasting your time with useless info.

If a moderator can remove my Post #10, please do- it's too late to edit (unless I missed something)
I'm gonna have to dig deep into the memory vault for this one.

However, when I have replaced impellers on recent model year Mercury OBs, the only thing that was a common cause of it hanging up on the way in was the tube that moves the water into the upper not lining up but it has been about 3 years since I worked on one of these.

That also makes me want to take back the comment about not doing this while the boat is in the water since the lower GC is much lighter than what's on a sterndrive.
 
On many Mercury motors the clutch dog is spring loaded.-------So if you remove the gear box in neutral it often jumps into forward.----Then you can put control in forward.-----And as always if you understand how they work it becomes much easier.
 
I'm pulling a quote from your original reply:
"Try and position/center the shift shaft in the motor housing to align with the shift stub on the LU"
I'm guessing the 'shift stub' is the foot mentioned by Jim, and he indicates they must align and come together but can't be forced. I would concentrate on confirming this detail when you attempt to reassemble after pulling the LU again. Also, I noticed a bushing in one of the diagrams. The bushing appears to seat in the hole through the bell assembly. Make sure that the upper shift shaft and bushing are properly seated in the bell housing. This is reminiscent of my problem, I did not get the shaft through the hole in the cowling, and therefore the LU would not come together, which had the same gap you had with yours. Just speculating here, but that bushing probably acts as a guide to marry the upper shift shaft with the lever, which if not correctly set, the helm shifter will not engage to switch gears. So foot and bushing, that's where I would focus..let us know when she's back on the water proper!
Mike
 
How long is the shift shaft? It should have its own hole in the upper GC, am I correct? The drive shaft and water tube are in the same cavity.
 
siluetae137 said:
I'm pulling a quote from your original reply:
"Try and position/center the shift shaft in the motor housing to align with the shift stub on the LU"
I'm guessing the 'shift stub' is the foot mentioned by Jim, and he indicates they must align and come together but can't be forced. I would concentrate on confirming this detail when you attempt to reassemble after pulling the LU again. Also, I noticed a bushing in one of the diagrams. The bushing appears to seat in the hole through the bell assembly. Make sure that the upper shift shaft and bushing are properly seated in the bell housing. This is reminiscent of my problem, I did not get the shaft through the hole in the cowling, and therefore the LU would not come together, which had the same gap you had with yours. Just speculating here, but that bushing probably acts as a guide to marry the upper shift shaft with the lever, which if not correctly set, the helm shifter will not engage to switch gears. So foot and bushing, that's where I would focus..let us know when she's back on the water proper!
Mike
Click to expand...
I think you're referring to a sterndrive and I did the same think until yesterday, when I saw that this thread is for an OB motor.
 
RickR90s said:
The shift shaft comes down from inside the motor housing and I would estimate its about 24" long.
Click to expand...
IMO, it would be easy if they used the Johnson method and extended the shaft all the way to the powerhead and make it move up & down but I doubt Bombardier wants to give up the patent.
 
Yes Jimn I was referring (incorrectly) to your diagrams. I screwed up too, which is odd because mine is an OB - so no initial confusion - then later I didn't bother dbl checking Ricks orig post which clearly indicates OB...sorry Rick.
Regardless, the issue still resides in the shift shafts movement in relation to some other component(s) or impediment in the dynamic with the GC or upper cowling/lever. Crossing fingers for you at this point Rick....
Mike
 
siluetae137 said:
Yes Jimn I was referring (incorrectly) to your diagrams. I screwed up too, which is odd because mine is an OB - so no initial confusion - then later I didn't bother dbl checking Ricks orig post which clearly indicates OB...sorry Rick.
Regardless, the issue still resides in the shift shafts movement in relation to some other component(s) or impediment in the dynamic with the GC or upper cowling/lever. Crossing fingers for you at this point Rick....
Mike
Click to expand...
I don't know who the moderators are, but a longer window for editing would help.
 
If they haven't changed the setup since the 70's:
This is how I do it in about 60 sec.: Turn the LU shift shaft by hand counter-clockwise until it
stops, then with Vise Grips tight on the bottom of the shaft turn it a
few more degrees CCW until it clicks into a stop, this
should be neutral - check by turning propshaft --
prop should spin freely.
Put control in N and go ahead and attach LU to driveshaft housing some turning of the flywheel will help the DS splines align.
Do not shift into reverse unless you turn the prop at the same time.
 
Reporting back. I turned the pontoon around at the dock and dropped the lower unit again. I wanted the pull the shifter shaft out of the lower unit and manually insert it into the female shaft in the engine housing to ensure it would engage.

It wouldn't. Upon closer inspection, the male shaft (LU side) had several burrs and cuts, that was interferring with engagement.

About 1/2 hour on the bench was spent cleaning up all the rough spots and then I verified it would manually insert into the engine housing. When I was satisfied, I applied a light smear of grease, and then placed a rag under the engine housing shaft to "lift it up a bit".

With the lower unit in forward and the helm in forward, it slid mostly all the way. I snugged it up and had my wife verify that the helm shift lever would move forward and reverse.

Success! A trip around the lake verified all is well.

Thanks to all of you for your help.
 
I work on old BMW motorcycles and at one point they went to a 2 piece driveshaft. Removing the rear end would allow the front DS to lay in a non-aligned position, so the towel trick would get it in the right plane so to speak. to push the differential in place with it's male end of the driveshaft. There's probably a better way, but it's what I know.
FWIW, that little white nylon piece that goes over the stub shaft in the lower unit doesn't really align s*^t. LOL
 
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