Causes for spun engine coupler? Looking for some help.

[markb8763]

Thank you all in advance. We recently received an 86 citation with a 140 merc alpha 1 gen 1. We replaced the bellows, water pump assembly, lower shift cable, gimbal bearing, and throttle controllers. We did not check the engine alignment but the sterndrive went back on, engaged the splines easily. I did have to give a bit of a kick and walk on the last 1/2 inch. I'm thinking that was due to the new o rings on the shaft. Everything ran well after some minor adjustments- shifted well into forward, neutral, reverse etc. We had it in the water for 45 minutes and then upon returning to dock, it would not shift out of forward, it idled slowly even when controller was in neutral. At some point while trying to get it out of forward, we heard some major whining coming from the engine. After pulling the cover we saw the drive shaft was not turning- I'm assuming the coupler is spun.

My questions- I'm going to replace the coupler and have an alignment tool on the way. I know the first thing that comes to mind is the alignment, but I don't understand how simply replacing the gimbal bearing would have an effect on the engine alignment if it was seated correctly. What else may have caused the coupler to go bad and what specifically should I check to be sure I don't trash this coupler as well?

 

[alldodge]

did have to give a bit of a kick and walk on the last 1/2 inch

That last 1/2 inch was telling you there was an alignment issue. You should never have to kick, or push real hard to get the drive on, O rings will not cause this kind of problem

The old gimbal bearing had some slop, but may have been doing some damage to the coupler, so when the slop/play was removed with a new bearing, the coupler just gave up

 

[Scott Danforth]

What else may have caused the coupler to go bad and what specifically should I check to be sure I don't trash this coupler as well?

checking alignment is an annual event along with greasing things, and inspecting the u-joints and gimbal bearing.

getting 33 years out of a coupler is pretty good.

 

[JASinIL2006]

AllDodge, do you think the problem with the last inch or so would necessarily indicate a problem with alignment? I mention this because, in his excellent video on installing an Alpha drive, achris describes why the drive gets hung up at that point and how to deal with it. (The discussion comes at about 2:25 in the video.)

If alignment was bad enough to spin the coupler, I would think he would have noticed difficulty before that point. In my experience, even with a properly aligned engine, the drive still can get hung up as he describe. In any case, would a drive that is a bit out alignment with the engine suddenly cause a spun coupler?

 

[alldodge]

Have watched the vid before, and I have not had the need to use the kick method, but do understand the premise. Never needed more then a push with my hand, if its all good.

Guess I should say, that not using an alignment bar leaves everything thing open if it was correct or not. The coupler could have already and probably was damaged, don't know

 

[harringtondav]

I have an old coupler yoke that will slide into a misaligned engine. But the alignment tool is always a no-go. The spline end of the tool is a close fit with the coupler spine bore/minor dia. If misaligned the shaft and coupler splines will fight each other every rev until until something gives.

 

[harringtondav]

I have an old coupler yoke that will slide into a misaligned engine. But the alignment tool is always a no-go. The spline end of the tool is a close fit with the coupler spine bore/minor dia. If misaligned the shaft and coupler splines will fight each other every rev until until something gives.

Edit. My bud"s 24 Ur old boat wouldn't align. Turns out he had transom rot. When you pull your engine you'll have the best chance to check this out.

 

[markb8763]

Thank you all for the input. Obviously I will check the alignment when I pull the drive off again. Any thoughts on why I couldn't get it out of forward and into neutral? That part is bothering me. Could something in the lower unit stuck and caused strain on the coupler?

 

[achris]

If it's stuck in gear, and trying to pull it out of gear doesn't stall the engine you have a shift interrupt switch problem, out of adjustment or failed, Or a broken lower shift cable, or it's come loose in the end from where you assembled it, or you missed one of the washers on the lower shift shaft, and the intermediate shaft has dropped low enough to lose engagement with the upper shaft and so it's not coming out of forward.

The coupler... As already alluded to, if the engine mounts have 'settled' over time the alignment will be out. As it settles the yoke and coupler splines wear. That will also put side loadings on the coupler. The drive sliding on easily is no confirmation of a correctly aligned engine/coupler... There is only one way to get the alignment right, with the proper alignment bar....

Chris.......

 

[Rick Stephens]

I'm wondering after reading this whether the splines were what gave out as opposed to the rubber in the coupler. Spline damage doesn't take very much misalignment and if you mix in a little lack of grease, they can go south fast.

 

[markb8763]

UPDATE- I removed the sterndrive and found the splines of the coupler were embedded in the drive shaft, so it was the splines not the rubber like Rick suggested. The alignment tool went in smoothly- now of course there are no splines on the coupler but it has to be really close. Before I took off the sterndrive, I checked by spinning the prop, it went into forward, neutral, and reverse easily. My big concern is replacing the coupler and engine mounts and then blowing it again. Does this new info suggest any other thoughts?

 

[alldodge]

The alignment tool went in smoothly- now of course there are no splines on the coupler but it has to be really close.

Your statement is not clear (probably just me) but I'm assuming, that the splines where destroyed and none were left. So new coupler is installed and alignment bar went in with 2 finger push in, and 2 finger pull out. If this is the case, then no worries, install the drive and your good to go

 

[Rick Stephens]

UPDATE- I removed the sterndrive and found the splines of the coupler were embedded in the drive shaft, so it was the splines not the rubber like Rick suggested. The alignment tool went in smoothly- now of course there are no splines on the coupler but it has to be really close. Before I took off the sterndrive, I checked by spinning the prop, it went into forward, neutral, and reverse easily. My big concern is replacing the coupler and engine mounts and then blowing it again. Does this new info suggest any other thoughts?

Alignment has no effect at all on gear selection, selecting forward and reverse and neutral spinning freely is all done at the bottom of the outdrive.

The only thing a good alignment does is keep pressure off u-joints and gimbal bearing and protect the coupler. A bad alignment can eat a coupler quickly, either by simply vibration working it really hard every rotation, like a chattering dremel tool, or by overheating and melting the rubber.

 

[Maclin]

UPDATE- I removed the sterndrive and found the splines of the coupler were embedded in the drive shaft, so it was the splines not the rubber like Rick suggested. The alignment tool went in smoothly- now of course there are no splines on the coupler but it has to be really close. Before I took off the sterndrive, I checked by spinning the prop, it went into forward, neutral, and reverse easily. My big concern is replacing the coupler and engine mounts and then blowing it again. Does this new info suggest any other thoughts?

Sounds like you have not replaced the coupler yet? If not, then alignment is not possible yet, using the tool now to obtain a reading means almost nothing.