Need Assistance to Diagnose Bravo 3 - 5.0L MPI Vibration

[BradsBoat]

Greetings,

Seems I'm in a bit of a pickle.

History

• No vibration
• The coupler was worn
• Installed new coupler & gimbal bearing
• Alignment tool moves w/2 fingers

Now there’s a noticeable vibration

• 1000 - 3200 RPM (didn't go higher)
• This is noticeable both when tied up to the dock in neutral
• And even more when on plane

Starting to investigate

• I pulled the drive and rechecked the alignment- still moves with 2 fingers.
• Noticed the Green Mercury Extreme grease on the drive shaft spline turned gray after only 6 miles - less than an hour
• There’s no noticeable wear on the shaft or gimbal
• U-Joints appear to be intact

ANY THOUGHTS ON POSSIBLE CAUSES?

• Bad Coupler?
• Bad gimbal bearing?
• Alignment? Had to pry the engine to towards the port side to align
• Incorrect installation of the coupler?
• Bad harmonic balancer? (no noticeable movement while engine is running)
• How about the 18 year old U-Joints? (No grease fittings)
• Would a worn outdrive splined shaft flop around in the gimbal bearing?

What steps should I go through to diagnose it?

Brad

 

[Fun Times]

Maybe improper orientation of the engine coupler bell housing / rear mounting bolts hardware can cause vibrations like this.

 

[BradsBoat]

Either seems likely.

Regarding the coupler bell housing orientation, the holes appeared to align. If I missed something, seems there should be a visible gap.

There might be something with the rear mounting hardware. It was a bolt, then washer, then spacer. I had to put some torque on those bolts with a pry bar on under the front of the starboard side of the engine to get the coupler to align properly with the alignment tool and the gimbal bearing. I rechecked the rear bolts and they were tight.

What would be the recommended way to diagnose this?

 

[Fun Times]

What year is your boat?
Try inspecting the rear motor mounts so they appear even…The following are some tips that help cover some of the things you’ve done recently.
https://static.perfprotech.com/files/images/mcmServiceBulletin.PDF

https://www.offshoreonly.com/forums/attachments/general-boating-discussion/576609d1582674427-bravo-coupler-bolts-bul-2009-11-coupler-install.pdf

 

[nola mike]

. I had to put some torque on those bolts with a pry bar on under the front of the starboard side of the engine to get the coupler to align properly with the alignment tool and the gimbal bearing

Are you saying that you needed the pry bar to get the alignment tool in? Or was that just initially when setting up?

 

[BradsBoat]

Hello Fun Times and Mike,

Thanks for the great info! Mine is a 2004 (OM69xxxxx). It has the newer style rear mounts.

I followed the Mercruiser instructions that came with the coupler, basically the same instructions in the service manual which likely pre-date the Service Bulletin 2009-11. The instructions didn't mention anything about getting tapered screws to set it. Maybe that's the problem, certainly a misaligned coupler would cause the symptoms I'm experiencing.

If we assume the coupler is in alignment, is there any chance there might be issues with the drive shaft and/or u-joints that could cause this? My mechanic. strangely I have a mechanic even though I do most of the work, is saying it's likely the u-joints. He's recommending the entire u-joint assembly because he says the splined shaft needs to be replaced when replacing the coupler. By visual inspection the splines appear to be in great shape and applying a little pressure to the u-joints didn't show any movement within the caps. So if it were the u-joints and worn splined shaft, it would have to be at a level beyond my ability to see or feel it. is this possible?

Regarding the lateral alignment, I used a pry bar (actually a 1.5" square pressure treated 2.5' piece of wood) to incrementally move the front of the engine slightly to the port side. Each time I removed the alignment tool and then re-inserted it to check the alignment.

Attached are two pictures showing where the green grease turned gray after less than an hour of operation. Also, there's a short video showing the two finger test on the alignment.

 

[nola mike]

However you did it, it sure looks like it's aligned now. Only thing I might try is to rotate the engine and make sure that the alignment stays in check throughout its rotation. The coupler splines are aluminum versus the harder steel splines, so much more likely to do coupler damage (I've never heard of anybody wiping out the drive shaft splines). U joints are always a possibility.

 

[Scott06]

However you did it, it sure looks like it's aligned now. Only thing I might try is to rotate the engine and make sure that the alignment stays in check throughout its rotation. The coupler splines are aluminum versus the harder steel splines, so much more likely to do coupler damage (I've never heard of anybody wiping out the drive shaft splines). U joints are always a possibility.

Agreed check coupler runout by rotating engine

also since u said vibration is present in neutral , run the engine with the drive off to see if you have the vibration or not. Possible you have a miss in engine? admittedly a long shot but he drive is already off...

The coupler looks fine but might be worth replacing the u joints ( easy to do and non merc cross refences are available) and input shaft . I wouldn't spend the money on a whole shaft unless I was paying someone to press out the joints. Ball joint press tool works very good for this

 

[BradsBoat]

Thanks Mike and Scott! I'll check the alignment in several locations by rotating the engine later today.

Running the engine without the drive would be a new feat for me. Should I just run it without running water for a minute or should I get someone to hold a hose up to the open water port on the bell housing?

Also, any thoughts on the color of the grease? Should it have turned gray in less than an hour of usage?

 

[Scott06]

Thanks Mike! I'll check the alignment in several locations by rotating the engine later today. Any thoughts on the color of the grease? Should it have turned gray in less than an hour of usage?

I would expect it to turn I use lucas red n tacky it comes out black after a season . Im sure they is left over grease on the input shaft

 

[Scott06]

Thanks Mike and Scott! I'll check the alignment in several locations by rotating the engine later today.

Running the engine without the drive would be a new feat for me. Should I just run it without running water for a minute or should I get someone to hold a hose up to the open water port on the bell housing?

Also, any thoughts on the color of the grease? Should it have turned gray in less than an hour of usage?

Jam a hose in the water port on the bellhousing where drive goes on. I think cutting an old washing machine hose in half works well. Doesn't need to be 100% water tight

 

[Grub54891]

Had a few in the shop that developed a vibration. Just another one yesterday. Nothing to do with the drive. Turns out if you have the flat distributor cap, it’s most likely misfiring causing a vibration. Yeah any dizzy can do that from lack of service but them flat caps do it more often.

 

[tpenfield]

I think you have gotten some good advice so far. . . being on my 3rd boat with Bravo outdrives, I'd offer the following:

U-joints can seem good to the touch, but actually be bad under load. So, you could replace the U-joints.

Alignment at 90˚ rotations of the engine as mentioned.

Not sure how quickly grease would dis-color in a new coupler, but the 90˚ rotation and associated alignment check would give indication to a defective coupler.

Gimbal bearing . . . maybe it was defective (???)

As you may know, Bravos do their shifting of gears in the upper unit (cone clutch). So, if the vibration is different in/out of gear, it may indicate a problem further down in the drive.

Outdrive is full of high performance gear lube?

Sorry if any of my comments are redundant, but just wanted to share my thoughts

 

[BradsBoat]

I appreciate the insight, experience and expertise! In addition to checking the alignment, and possible misfire, I'm going to run most of the straightforward items to ground with new u-joints and another gimbal bearing (all Mercruiser parts). Regarding Bravo upper unit (cone clutch) in/out of gear, running the engine without the drive would seemingly locate the vibration beyond the coupler. I'll have to wait and see if it's still there after the replacement parts are installed. While a defective coupler is unlikely, it would be really bad news. Waiting on parts now, I'll follow up next week with more info.

 

[Grub54891]

Had a few in the shop that developed a vibration. Just another one yesterday. Nothing to do with the drive. Turns out if you have the flat distributor cap, it’s most likely misfiring causing a vibration. Yeah any dizzy can do that from lack of service but them flat caps do it more often.

Have you checked this?

 

[BradsBoat]

Not yet, I meant to add that to the list in my response. I'll check the cap first given it's one of the easier possible items to fix. It makes sense that a misfire from a bad cap would cause a vibration that feels like something is out of balance. The cap is new, but I kept the old one for a spare.

 

[dubs283]

The cap is new

Ensure firing order is correct

 

[BradsBoat]

I ran the engine without the drive attached and there was still a vibration. It also seemed to have a misfire. I replaced the cap as suggested by Vice Admiral Grub and the misfire is no longer there! The cap I replaced was a brand new AC-Delco. I used that brand thinking it would be ideal since it's the one GM uses. The replacement cap was a no-name brand I had sitting around.

There's still a vibration, but it's now only at the higher RPMs - 3000 and above, and not at the lower RPMs. Maybe that vibration at the higher RPMs was there before, maybe not. I'll know for sure once I get it out on the water.

Since the u-joints are 18 years old, there're getting replaced today. I'll provide an updated status after the sea trial.

Thank you all for helping me!

 

[Grub54891]

I ran the engine without the drive attached and there was still a vibration. It also seemed to have a misfire. I replaced the cap as suggested by Vice Admiral Grub and the misfire is no longer there! The cap I replaced was a brand new AC-Delco. I used that brand thinking it would be ideal since it's the one GM uses. The replacement cap was a no-name brand I had sitting around.

There's still a vibration, but it's now only at the higher RPMs - 3000 and above, and not at the lower RPMs. Maybe that vibration at the higher RPMs was there before, maybe not. I'll know for sure once I get it out on the water.

Since the u-joints are 18 years old, there're getting replaced today. I'll provide an updated status after the sea trial.

Thank you all for helping me!

Well the spark plugs are next? I refuse to use champions on anything anymore, nothing but trouble.

 

[QBhoy]

I was so keen to mention the cap. But I say it all too often on here. Just such a common thing with these.
Anyway. It won’t do any harm, if it’s not that. If you are now getting issues around 3000 rpm…it won’t be anything too serious, as perhaps eluded to previously.
I think sometimes we are all too quick, to assume the worst. Perhaps just my optimistic thinking, but really feel that it’s best to start with the simple things first. If nothing else…at least start with the well known and common issues first.
At the very top of the list on these particular engines…by a long long way, is always one of a couple of things.
Top is the diz cap for sure. Just ridiculous common now.
Second thing that helps these run better or as they should…is having the correct plugs in them. They need a minimum of platinum…but even they run poorly. Without doubt…the iridium ngk plugs are what you need.
Any hint of a deteriorating battery…forget it. Get a new one. They just won’t play without it. I could bore you with a few other issues for sure. But they are the usual suspects. For your situation at least. I’ve put nearly 1000 hours on my mpi and had to figure it all out myself over here in the uk…where they aren’t (or weren’t) too common or well known to most dealers. Once you get on top of them…amazing things.