View Full Version : Shaft coupler stuck

07-26-2010, 05:55 PM
Complete V-drive Newb here-- just upgraded to a 2001 X-30 with 280 hours on it from a 1989 Mercruiser I/O. I worked on the I/O a lot, but have never worked on a V-drive boat before, so I'm new to these beasts and their idiosyncrasies.

We love the new boat, but it has a few quirks that I've got to iron out.
I discovered that it takes 2 hands to turn my prop when in neutral, so I figured it was an alignment issue (there doesn't seem to be any vibration when running, some "gear noise" at idle and intake "whining" at high speeds-- but from I read these are normal)

I tried to undo the coupler to check alignment, but when I got the bolts off I could not separate the two halves of the coupler--no gap anywhere around. So I wimped out and took it to a mechanic. He didn't separate the coupler, but told me the shaft is bent (by using a straightedge maybe?) Is it possible to have a bent shaft but little/no vibration?
I'm unsure of the mechanic's answer now, so I might have to get back into it myself.

How do I separate coupler halves that are stuck together? What can I "bang on" without damaging bearings, etc. Do I hit the end of the prop shaft and try to drive the shaft forward in the boat and the coupler halves apart? Or do I try to pound a wedge/knife edge between the coupler halves in hopes of prying them apart?

I know this coupler stuff and alignment has been covered extensively in these forums, but I haven't seen anything on stuck coupler halves.

Thanks for any help you've got.

07-26-2010, 06:35 PM
I had this problem in the spring when I checked my alignment. I soaked the coupler in PB blaster for a few hours and then took a wood block and mallet and firmly whacked the coupler on the shaft side (the shaft has some play available unlike the transmission side). I would hit it and then spin the shaft 90 degrees and repeat. I then went under the boat and pulled on the prop towards the rudder. It separated after that.

07-27-2010, 09:15 PM
If your shaft is indeed bent make sure to check the strut as well. You can remove the prop and tap the end of the shaft to separate the coupler, should come right off. Now the shaft nut is another story!

And yes it is possible to have a bent shaft with minimal vibration.

08-13-2010, 11:43 AM
Thanks for the advice on separating the stuck couplers-- with a bit more thought on the subject I realized that the coupling takes the entire thrust of the prop under power, so I shouldn't be worrying about damaging transmission bearings by hitting on the end of the prop shaft a bit to separate the coupler.

We asked around a bit, and found that the first mechanic wasn't really a V-drive expert, he's better with I/O and outboards. So we went to a second mechanic who's highly recommeded for high end ski boats. (since we're new to the whole V-drive thing, I wanted to get a clean bill of health from an expert in case there's things I just don't know to look for, then hopefully I'll be able to handle it from here on out)

Anyway, the second mechanic said that the strut bearings can sometimes be a bit tight (which he said explained the prop shaft being hard to turn in neutral). But he said that everything is fine, no bent shaft!

I *like* his answer a lot more, but there's a lot of people on this forum who say the prop shaft should be easy to turn. Not quite sure if I should believe the new mechanic either-- guess if you want something done *really* right you've gotta do it yourself. So I think I'm just going to leave it alone for the rest of this season, since it seems to run really smooth (no vibration); and next season I'll pull the coupler apart and see if I can align it better than the mechanic and get a more freely spinning prop shaft.

08-13-2010, 12:30 PM
Being a country boy and having grown up working all kinds of boats I picked up some simple tricks. I worked on boats every summer and after school for my first real job. Take a welding rod and tape it to a reference point that doesn't move. Turn prop slowly and easy by hand. If shaft is bent it will show. Application of turning force needs to be a constant in location and pull. We also do this for propellers large and small. We just find a different reference point to secure to near whatever we are using to see wobble. You can sometimes locate the bend doing this by moving reference rod up or down the shaft. If you see wobble that makes sense then it is time to break out the tools or get a better opinion. We it comes to alignment I would make sure that I have a alignment problem before I create a alignment problem.

08-13-2010, 01:13 PM
If the strut-to-engine alignment is off, then it will force a bend in the driveshaft. If you check straightness with a straightedge, you'll probably be able to pick it up. However, if you check using a oldairboater's technique (or with a higher-tech dial indicator), you won't see it - the shaft won't "wobble" as it turns, but it'll be bending back and forth all the same.

I still recommend doing the propshaft alignment; if you seperate the coupler, I think your problem will become obvious - the shaft side will move relative to the transmission side.


08-13-2010, 01:27 PM
Double post I was thinking too hard. If the strut-to-engine alignment is off, then it will force a bend in the driveshaft. If you check straightness with a straightedge, you'll probably be able to pick it up. However, if you check using a oldairboater's technique (or with a higher-tech dial indicator), you won't see it - the shaft won't "wobble" as it turns, but it'll be bending back and forth all the same.

I still recommend doing the propshaft alignment; if you seperate the coupler, I think your problem will become obvious - the shaft side will move relative to the transmission side.


08-13-2010, 01:31 PM
Welding rod is a quick simple trick and saves me from dragging out indicators. I can see how couple alignment would be easier to see with split couplers but a dial indicator should detail any lateral movement in a shaft if the shaft is bending anywhere. Bend back and forth isn't a wobble that a dial indicator would see? What am I missing?
If the strut-to-engine alignment is off, then it will force a bend in the driveshaft. If you check straightness with a straightedge, you'll probably be able to pick it up. However, if you check using a oldairboater's technique (or with a higher-tech dial indicator), you won't see it - the shaft won't "wobble" as it turns, but it'll be bending back and forth all the same.

I still recommend doing the propshaft alignment; if you seperate the coupler, I think your problem will become obvious - the shaft side will move relative to the transmission side.


08-13-2010, 04:06 PM
Take a straight shaft. Attach something to each end - say, an engine on one side, and a prop on the other. Bolt the engine to something solid. Now, move the prop six inches to the right, and bolt it to something solid.
If you look at the shape of the shaft, it will be bowed - it has to be to get from where it wants to be (straight back), to where it is (six inches right). If you rotate the shaft, the bow will stay in the same place relative to the boat (it won't "wobble"). If you put a straightedge on the shaft, you'll see the bow and can measure the 6 inches. However, if you attach a dial indicator (or welding rod) to the boat to check for straightness and rotate the shaft, there won't be any wobble - the shaft will always bend the same amount when measured at the same location. If you disconnect the engine and the prop, the shaft will now spring back into position, and be perfectly straight again.

If the shaft was bent before you started all this (i.e. with no forces on it), then using the dial indicator or welding rod will tell you that - you'll be able to see the bent spot as it rotates; it'll "wobble".

At least that's the way I understand it.


08-13-2010, 09:19 PM
Miker, that sounds right to me, try moving the prop right after you pull it out of the water. If the prop turns easier and you feel smooth rotation I wouldn't worry.

Now when you are done for the season listen to what FrankSchwab is saying as he is spot on. You sound like you have some experience with mechanics and once you read the engine alignment threads on this forum it will all click.

Have fun:D

05-24-2011, 01:35 AM
OK, so I didn't work on the boat _all_ winter... kids, winter sports, desert trips, and *gasp* work took up all my time. But it's getting warm, so the boat is back on my mind and I've started trying to figure out my drive shaft alignment again.

This time when I went to separate the shaft coupler, all it took was a smart knock on the prop end of the shaft with a rubber mallet and the coupler came apart. The shaft end of the coupler immediately shifted over sideways about 1/2". I removed the shaft seal and the rubber hose at the log to see if that was causing the sideways motion, but the shaft still wanted to stay to the side. So I took a look at the strut. No signed of impact or being bent, but it is clear the bearing in the front of the strut has been heavily worn on one side. In its "natural" position through the strut, the shaft is off center on the log, and the wear on the bearing is obviously from the side load applied to the bearing when the shaft is pulled into the center as it was mated up to the V-drive coupler.

I called up the shop that checked it out for me and they told me, "That's not the correct way to do an alignment. You need to leave the bolts in and simply check the angle i.e. the gap around." When I mentioned the uneven wear in the strut bearing, he told me, "Is there any slop or play? If there's no wiggle, then it's fine." Well, of course there's no wiggle because the shaft is pushing sideways onto the bearing! This shop is not an MC shop, but they are another high end ski boat brand and they come recommended as the best ski boat mechanics for about 2 counties around... (my nearest MC dealer doesn't respond to phone calls and is 2 counties away on the other side of horrible Los Angeles traffic from me...)

From what I'm beginning to gather, MC and the other boat manufacturers don't seem to worry too much about the "strut alignment" (as it is called on this forum) and just worry about the "engine alignment" that gets the angle right to avoid load on the V-drive bearings.

05-24-2011, 01:43 AM
...oops, hit enter before I was done...

Anyway, being an engineer and a machine designer, this lack of strut alignment really bothers me. Maybe the machine will run up to 100s of hours with this kind of problem, but it certainly doesn't give me a good feeling.

I was going to ask if anyone knows any good MC mechanics in the Los Angeles or Ventura County areas... but I think I'm just fed up with not being able to find a mechanic that thinks like I do, so I'll just have to deal with this myself.

I think I'm going to try the "yank" or "whack" on the strut method that has been mentioned a number of times in various posts-- I just need to get the front of the strut to move maybe .020" to the port and things would line up really nice...

Other option would be to replace or remount the strut-- if I was sure the strut was bent I'd do that, but I still think there's >50% chance that it came from the factory like this, so a new strut might be exactly the same.

I can say for sure that the difficulty turning the prop came from all the binding due to the shaft being pulled to port to mate with the V-drive. As soon as I disconnected the couplers and removed the packing nut and rubber hose at the log, the prop became very easy to turn. Now if I can just find a way to keep that when I put it all back together.

I'll post an update when I try something and find success or failure...

05-24-2011, 07:05 AM
When I first bought my 210 it was really out of alignment. It was so bad the shaft was in contact wit the big brass packing nut. Your boat may have a dripless system in it, which means you wont see a big nut but more of a seal.

Anyway, I had to unbolt the strut, replace bearings, aim the prop shaft into the center of the through hole and tighten the strut back up. Once all this was done then I could do the prop shaft alignment which you seem to realize it's more then moving the engine and trans around rather then the shaft.

There wasn't a ton of room to move the shaft around by moving the strut but it was more then enough to get it centered in the log.

05-24-2011, 01:02 PM
I would first try a full alignment as shown here (http://www.mastercraft.com/teamtalk/showpost.php?p=701305&postcount=14).

Now that you have the coupler seperated, unclamp and slide the packing box up the shaft. See if the "natural" position of the shaft goes through the shaft log without touching the sides - if so, the engine alignment is the simplest approach. If the shaft hits the sides of the log, then you'll probably need to move the strut. Unbolt it, break it loose from the sealant, clean up the surfaces, reapply sealant, loosely bolt it in place, apply necessary force to get it through the log cleanly, then bolt down tight.


05-25-2011, 04:50 PM
OK, I got the packing and coupler all loose and the drive shaft still hits the side of the log-- in fact it's kind of wedged between the angle the strut wants it to be and the side of the log-- not extreme, but snug. It takes a good bit of pressure to pull the shaft off the side of the log. So I'm pulling the strut off to see if I can mount it any straighter, or else I'll get a new strut. What do you recommend sealing it back up with? Will Home Depot silicone sealant do, or is there some special marine grade stuff that should be used?

05-25-2011, 05:00 PM
I hate it when my shaft coupler gets stuck

06-28-2011, 12:46 AM
OK, been through a lot, which I'll try to explain since reading others' trials has helped me so much on this site...

When I got the couplers apart I found that the strut was pushing the shaft quite hard against the side of the log. The engine was set up such that the shaft needed to be pulled sideways (to the center of the log) to connect the shaft couplers, so it wasn't hitting the log when coupled, but it was placing the shaft through the strut into a bit of a bind-- this is what was causing the difficulty in turning the prop by hand. I could also see that the strut bearing was a lot more worn on the side the shaft was being pulled to.

I talked to a mechanic who said, "the strut bearing is fine as long as it is not flopping around." He was also not concerned about the fact that I needed to pull the shaft over to connect the couplers-- he said as long as the "angle" i.e. the gap between the coupler faces was OK, then the alignment was good.

I've seen this sort of opinion posted elsewhere, but I've also seen a *lot* of smart people here who suggest the engine alignment should also be done to eliminate the need to pull the shaft over. I decided that while it might work for a while the way it was, it would certainly wear out the strut bushing faster, and might be putting extra side load on the V-drive bearing that I didn't want there.

I tried bending the strut enough to center the shaft in the log with big wrenches and ratchet straps-- I could flex the strut enough to get the shaft centered, but when I let the pressure off it would go back. It seemed like it was going to take a _lot_ more oomph to actually bend the strut (rather than just flex it). It also looked like there was not going to be enough space on the strut mounting area to remove and replace the strut slightly twisted enough to line up the shaft so I gave up on the old strut and ordered a new one.

The new strut came in and looked identical to the old one. When I placed them side by side and did careful measurements between them I could see that the two struts were at slightly different left-right angles-- hence my old one was indeed slightly tweaked.

Installing the new strut was pretty straightforward-- especially after reading all the advice posted elsewhere on TT. Once installed, the shaft was still not _quite_ centered in the log, but wasn't hitting the sides or anything.

I then proceeded to align the engine to the new strut, which required shifting the engine to the starboard about 1/2" or so. (I found that a large C-clamp could be used on the rear engine mounts to quickly, easily, and accurately move the rear of the engine...)

Finally I got the angle of the alignment correct (again following all the excellent instructions on TT)

Now I can turn the prop with a firm one-hand, or maybe even only a couple of fingers.

It was a bit pricey, and took a number of hours; but now I feel like it is set up to go 100 's ofhours more instead of having to worry about the strut bearing wearing out sooner rather than later.

Pictures below:
1) shaft pushed hard against side of log by tweaked strut once couplers were apart and log seal removed
2) Picture of new and old strut-- the slight angle difference between them can just barely be seen, it was easier once I measured front and back to know there was a significant difference
3) C-clamp used to slide engine laterally on aft engine mounts during engine aligment procedure-- there's nothing back there to wedge on, so I stuck trying to move the engine until I got the c-clamp idea.

06-30-2011, 03:52 AM
Glad to hear everything got "straightened out" for you.

After I got my drivetrain aligned, I noticed that the boat felt smoother - some amount of vibration disappeared ( though it certainly wasn't an issue previously), and I felt better about it when I could grab hold of the prop with one hand and rotate it.


ProStar Slalom
06-30-2011, 06:30 AM
Thanks for sharing, and great idea with the C-clamp. I'll keep that in mind if I have to do an alignment down the road.

06-30-2011, 06:37 AM
be glad you fixed it yourself, the accomplishment of DIY work after methodically finding out what was wrong is definitely worth some beers.

The guys who "worked" on our fire engines were parts replacers, you are a mechanic :-)

06-30-2011, 07:21 AM
Nice explanation and good information to have. It is sad that the professional mechanics you had available cannot or do not do it right whereas a "regular" boat owner figured it out and fixed it himself. Granted, you must be mechanically inclined in order to do this. I wonder if you heated the old strut if it could be re-aligned.

07-12-2011, 04:34 PM
I'm sure the strut could even be realigned with some good ol' brute force-- it would have to be bolted down to something really solid and a 1-1/8" diameter bar placed through the bearing-- then yank on it with a really long pipe "breaker bar". I'm convinced it could be bent back straight. But it would be pretty tricky to do as 'straight" is not obvious looking at it, and if you bent too far or not far enough it wouldn't really do much good. You'd need to fixture up some measuring tooling, or have another good strut available to compare with. Or keep putting it back onto the boat and checking until it was right, but this would be pretty time consuming! As I mentioned, I couldn't tell the strut was bent by looking at it, I could only tell when placing it next to a good strut and measuring.