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SubTopic :: Coupler Replacement
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John Hempel
posted 04-26-2004 5:49 AM

Please excuse my posting this in two forums. After I posted this question I noticed that I was in the OMC forum. I am posting it again here, so that it will be in the proper place. I didn't see a delete option for the other one.

I have a 5.7 L Chev. V-8 with a Mercruiser Outdrive. The boat is a 1984 model. I bought this boat used, and am not quite sure which Mercruiser outdrive I have, but I'm fairly sure it is a M or MR model. The engine coupler spun out this weekend. The engine is running, but the shaft isn't turning. The engine ran hot right away.

I have the outdrive off. The splines on the outdrive shaft look OK, but the coupler is almost smooth.

I have two questions. 1 is what causes this? The other question is, can the coupler be replaced if I take out the gimbal assembly, or do I need to pull the engine out?

I am a fairly competent auto mechanic. I am new to the marine outdrive work. I was able to change the water pump impeller last year with no trouble, following the manual.

Any tips and source of parts will be greatly appreciated.

I hate loosing the boat in the spring! The repairs will commence this weekend, after doing some homework this week.

posted 04-26-2004 7:46 AM

You said the coupler splines are smooth, you mean gone? Do you have the triangular coupler or the round one? Is the coupler held on with three bolts or six stud/nuts? I picked up my last coupler off Ebay. Do you have an alignment tool for the engine? Do you have a Mercruiser maintenance manual?

John Hempel
posted 04-26-2004 7:58 AM

Yes, the coupler splines are gone. It is a round coupler. I can't tell about the bolts looking through the hole in the gimbal, so I don't know yet.

I do have a shop manual. It covers the engine itself in detail down to overhauling the engine. It also covers the outdrive in detail. However, it doesn't mention the coupler, other than to say that you need to take the boat to a dealer for alignment! What a book ..... I will have to order a new one.

I will have to buy an alignment tool. I just got off the phone with a dealer mechanic who was very helpful. He did confirm what I already suspected, the engine will have to come out to change the coupler.

I see the next couple of weekends being ruined!

adam walker
posted 04-27-2004 9:58 PM

There are two reasons that generally cause an engine coupler to fail. Those are lack of proper engine alignment and lack of lubrication.

John Hempel
posted 04-28-2004 4:13 PM

Thank you, Adam. That concurs with what I've learned lately.

I never knew that fitting was there. It won't go long without grease now!

I've taken all the seating, brackets, etc. out of the way this afternoon. I disconnected the fuel line and wiring.

The marine dealer called this afternoon and said the coupler is in. I will pull the engine out on Friday.

I'm sure I will have some questions to post on Friday evening!

Thank you for this web site. I have learned a lot browsing the messages.

John Hempel
posted 04-30-2004 4:51 AM

I have one more question. It is a simple one. What are the torque specs. on the coupler bolts. I have looked this book over numerous times and can't find it.

Thank you!

adam walker
posted 05-01-2004 7:50 PM

John, At first my brain was telling me 55ftlb but the only manual I have at home is for diesel motors and it says 35ftlbs.Sounds about right though. Good luck

John Hempel
posted 05-02-2004 4:04 AM

I have the new coupler installed. I over tightened the coupler, if your numbers are correct. I tightened them to 65 ft/lbs based on a book on OMC a friend has. I was pleased to find that the ring gear and starter look like new. I did an oil, filter, and spark plug change while the engine was out. I lowered the engine back on the mounts, and have begun to hook everything back up. I ordered the alignment tool from Sterndrive.com. I'll have to wait on the reinstalling the outdrive until the alignment tool comes in. Are there any special tips you can offer on alignment? Thank you!

John Hempel
posted 05-07-2004 4:56 PM

I have almost completed this project. I am very close, but at a loss as to what the problem is. I have spent almost the entire afternoon trying to reinstall the outdrive. The splines go together. Everything slides in to within an inch or so, then stop. I can't get it close enough for the bolts to come through. I am open to suggestions.

adam walker
posted 05-07-2004 6:26 PM

How was the engine alignment? The tool shouldslide in and out freely using very little effort.Are you sure the drive is still in forward gear? Is the gearshift in forward gear?If the gearshift is in forward gear are the cables attached to the shift plate?,and did they move adjustment while the engine was out.

John Hempel
posted 05-08-2004 6:10 AM

I am not 100% sure that I am using the alignment tool correctly. I am just insert it and moving it around. It appeared as though the engine shaft was too low, so I lowered the front to get the rear to go up. The splines make up fairly easily in the beginning, but don't go all the way. I am not getting far enough for the gearshift links to meet, so I don't think that is a factor, yet. I have been paying attention to them. Both are in forward. I know the drive is because I am turning the prop shaft to get the universal shaft to line up. I am wondering if the thick gasket that goes around the universal housing is the culprit. It is out of sight at this point. I may remove it to see if things go together, in order to prove the point. I wish that I had thought of that yesterday. I'll let you know what I learn today. Is it required? It appears to me that if the main gasket seals, then this one is secondary.

John Hempel
posted 05-08-2004 6:35 AM

Is there a web site that shows the proper alignment procedure? I haven't been able to locate one.

John Hempel
posted 05-08-2004 4:27 PM

I finally conceded defeat and took the boat to the dealer today. I suppose I saved a great deal of money by pulling the engine and replacing the coupler. I decided that it might be best to have a "pro" check the alignment and reinstall the drive. This way hopefully I won't ruin the new one. The problem is that it will be a week before they get to it. It is boating weather here!

adam walker
posted 05-08-2004 6:26 PM

It's only gonna take them a week!!! Heck where I work we are three weeks behind.Well I'm sorry to hear you concede but you know the old saying "when in doubt, hire it out" At least with the alignment tool you can get a feel for what the alignment is supposed to feel like at the end of the season when you lube the u-joints and coupler again.

John Hempel
posted 05-11-2004 8:45 AM

It looks like it may be less than a week. He called me today to let me know that they have started on it. Where to you live, Adam? I don't know where Lake Arrowhead is. The boating season here is Georgia is well under way. The past few weeks have really warmed up.

John Hempel
posted 05-11-2004 10:24 AM

Help! Adam, I need some advice. My marine dealer called and said that the front mounts are adjusted all the way down, and are still too high. How could this be? Where do I get shorter mounts? At least now I know why the coupler went bad and why I couldn't get the drive back together.

adam walker
posted 05-11-2004 11:51 PM

Well John I'm not sure how to help you.It is possible that the center of the coupler wasn't pushed perfectly centered into the hub.I would ask them to turn the engine over 180 degrees and if the alignment goes the other way you may have a coupler problem.The only recommendation I have for finding lower motor mounts is contact mercury @ www.mercurymarine.com and go to the contact area start asking around. To answer your previous question I actually live in Crestline Ca, and work in Lake Arrowhead Ca.Which are only a few miles apart.You may remember mention of the Lake Arrowhead area from the Southern Ca fires last Oct.

John Hempel
posted 05-25-2004 4:55 AM

Here is an update on this project. It turns out that the motor mounts were installed on metal tubing. The "originals" were 4" X 6". I replaced them with 4" X 4" tubing. The up and down alignment seems to be correct. I have a slight problem with the left and right, with very little adjustment room. My big question is, how much is too much out of alignment. I was able to install the drive, but I had to put some force behind it. I haven't run it on the lake yet because I don't want to ruin the new coupler. I ran it on the hose and shifted gears. Everything is working. I am thinking about taking out the bolts that hold the mounts to the tubing. I can then scoot the engine over and weld the mounts in place. This can be done without removing the engine, again. The only problem I see is that there will no longer be any left/right adjustment. Of course, there isn't enough as is so I'm not losing anything.

Bill McKay
posted 05-29-2004 8:36 AM

It sounds like angular misalignment. The hole in the coupler is lined up, but the horizontal plane is a bit off. I'd like to hear that the drive slides in without any added force. The coupler won't live very long unless the alignment is almost perfect. I would go back to the rear mounts and make whatever correction is necessary to have the coupler on the same plane as the gimbal brg. There is very special grease for the splines by the way. As far as the alignment tool, I don't put that much faith in it. In fact I often use the handle of my 3/4 johnson bar. The tool along with a keen eye and the feel when the drive slides in so perfectly.... Are you saying up above that there's a grease fitting on your coupler? I've not seen that before...

John Hempel
posted 06-01-2004 6:03 PM

Thanks for the feedback, Bill. I am new at this, but learning fast! I can reach the drive shaft from above. I have learned more from feeling around it with the drive half on, than anything else. My comment about grease fitting was before I really got into this project. There is no fitting on the coupler. I used a high quality wheel bearing grease on the splines. What should I have used? I am still not very confident in the alignment. The drive goes on with little effort, except for the last 1/2 inch or so. I had to force it from there.

Bill McKay
posted 06-15-2004 8:19 PM

Mercruiser Spline Grease is what you want to use.

chris funk
posted 07-09-2011 10:11 AM

I have a 1986 5.7 liter V-8 260hp mercruiser. I have gone thru 3 engine couplers in the past 4 years. My mechanic tells me he does know why they are burning out so quickly and I an at a loss. I had a new lower unit and fumble bearing installed last year also. Is there anything that I need to look for this time? I am going to take it to a different shop in hopes of finally getting over this. The prop we are using is a 15 pitch because of the size and weight of the boat. The engine ran at 4500 rpm at wot. I don't believe that it is the problem but I have been good that the wrong prop could cause the oroblem also. Please advise.

Bt Doctur
posted 07-09-2011 12:53 PM

alignment goes bad from a few reasons assuming the factory did their part correctly.collapsed rear bushings allowing the rear of the motor to drop down and put pressure on the inputshaft.front mounting pads/stringers rotted allowing the motor to "torque over" under throttle.a rotted transom allowing the rear of the motor to flex around. That grease fitting means nothing, proper service is removing the drive at the end of the season, inspecting for water or gear oil in the boot, greasing the U joints, and checking alignment.

Wayne Lucas
posted 07-26-2011 10:40 AM

I too have had problems with the engine coupler. 3 times replacement. I have a 3 ltre mercruiser I/O that pushes a rather big tugboat. What I've just discovered is that the rubber that hold the spline center of the coupler can slips in its own housing. I need to find a coupler that is solid made out of metal

Bill McKay
posted 07-27-2011 6:49 AM

no you don't, Wayne. That rubber is a valuable torsional damper between the engine and drive. Replace it with solid one and the two will hurt each other....especially with a 4 cylinder engine...less cylinders = more violent power delivery to the drive. Stay with rubber and check alignment.

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