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mpm330

Vibration between 900 & 1200 rpm

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Last fall had engines tuned up and complete service on out drives. Since then I have noticed that the port engine has a vibration between 900 & 1200 rpm. Above 1200 & below 900 it smooths out. Had the mechanic down to the boat and from what he saw the coupler is wobbling at those rpms. He said it may require replacing. He has a call into the local Merc rep, but he is out of pocket for a few weeks.  The engine starts right up and is fine at idle and above 1200 it is also fine. The mechanic said there were no codes. While I wait for the Merc. guy to get back I had a couple questions.

1.  Is there something the mechanic could of done to cause the problem.

2.  Is it going to hurt to run it like this.  

 

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Coupler failures come in a few flavors. If you sheer the splines, then the engine RPM will take off faster than the rev limiter can get a hold of your 350. Kind of like stepping in front of a speeding train and saying hold-up there, never a good thing. I don't like his wobble comment as he did not state whether it was the out drive input shaft he saw oscillating, or the coupler body itself. If the body is bouncing around, then a catastrophic failure there could cause damage to the bell housing. Only ever saw that once on a high performance application, but it was not pretty.

All that said, if it is a spline tooth failure, you want it replaced before any damage is imparted to the out drive input shaft spline teeth. The coupler on the small blocks are aluminum, and the shaft is steel so typically the shaft will endure a coupler failure. As far as the service tech doing damage, he may have done a WOT run after the tune-up, pushing the failing coupler into the twilight zone, but I do not think blame can be placed there.

My question is why the failure occurred in the first place, and did it affect the gimble bearing, u-joints, upper gear case input shaft bearing set, and/or seals. Engine alignment is always a suspect here, or lack of lubrication to the coupler itself. These units are picky as they use dissimilar metals, and require a specialized extreme pressure lubricant, not a simple multi-purpose grease. If it were mine, I'd upgrade to the stainless steel coupler utilized on the big block engines, and make sure your other engine is both aligned properly, and greased frequently with the appropriate lubricant. The fitting spins as it is part of the coupler, so once you find it pointing straight up and accessible, you may want to mark the crank shaft pulley with a bright paint mark so you can find it next time with ease.  W

http://www.marinepartsplus.com/catalog/mercruiser/serial/350_MAG_MPI_ALPHA-BRAVO/8M0049000/15322-160

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Wingnut thanks for the input.  Last Nov. when the out drives were pulled they changed bellows an gimble bearings, plus aligned. The vibration was not there before the service. When they change the oil they also always lubricate the couplers (yearly). The engines are very low hours so it is hard for me see how the coupler is bad. I still think something else is going on.  When they did the service in the fall a complete tune up was also done with cap, rotor, and plugs. 

I have to say that the mechanics (father & son) at my marina are top notch and I have a hard time not trusting them. I guess I will wait to hear what Merc. rep. has to say. May have bite the cost and have the coupler replaced, just want to be sure before I have that done.

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7 minutes ago, mpm330 said:

Wingnut thanks for the input.  Last Nov. when the out drives were pulled they changed bellows an gimble bearings, plus aligned. The vibration was not there before the service. When they change the oil they also always lubricate the couplers (yearly). The engines are very low hours so it is hard for me see how the coupler is bad. I still think something else is going on.  When they did the service in the fall a complete tune up was also done with cap, rotor, and plugs. 

I have to say that the mechanics (father & son) at my marina are top notch and I have a hard time not trusting them. I guess I will wait to hear what Merc. rep. has to say. May have bite the cost and have the coupler replaced, just want to be sure before I have that done.

I would be interested to hear what he saw relative to coupler wobble. I bought a USB key hole camera for 20 bucks that I use to look where head won't fit anymore.  W

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Wingnut, if the out drive is pulled can the coupler be inspected for any damage before going to next step? I can't stop thinking that something happened to the gimble when they serviced it. There was no vibration before all the work was done last Nov.

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In business. I have received enough defective new parts.

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It happens. The mechanic tried a new cap and rotor even though he had installed then in the fall. He said he had seen a problem with the merc caps. 

Still waiting to hear from merc local rep.

I am headed over to the boat Monday or Tuesday and I am planning on checking with the shop then.

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23 hours ago, mpm330 said:

Wingnut, if the out drive is pulled can the coupler be inspected for any damage before going to next step? I can't stop thinking that something happened to the gimble when they serviced it. There was no vibration before all the work was done last Nov.

A coupler failure will usually distribute an appreciable amount of shred into the area where the driveshaft exits the engine bell housing. Rubber dust, or aluminum filings would be apparent. Also, after the drive is pulled, a bore scope can tell the story also, without need to pull the engine. Bad bearings right out of the box are rare, and I have seen it with Japanese sourced steel, but never in a marine application. I am not a fan of the new perma-lube bearings as there is no downside to routine re-greasing with the proper lube. Your tech is right about that vintage cap and rotor being a problem, but if that has been replaced and the condition remains, the your search continues. The good news is by pulling the drive, you can eliminate the coupler, u-joints, gimbel, alignment, input shaft bearings, and just for the heck of it, I would swap the props side to side if they are both the same rotation.  W

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Vibration happens in slip with throttle only, so probably not props. 

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19 hours ago, mpm330 said:

Vibration happens in slip with throttle only, so probably not props. 

Good information, and eliminates that possibility. W

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Well they talked to Merc. rep and no idea on what is the problem. So after talking with mechanic, they are going to pull the out drive this week and check u-joints, gimble and bearing. Then he is going to check alignment. Will see what they find. The option of replacing coupler is not something either of us wants to do. Hoping they find something.

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Could even be a engine or engine accessory.  Does it do the same vibration if driving around in F & R ?    Good luck with some sharp people.

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It is the same in or out of gear.  Today was a really nice day so I went out for a long run and it ran great when above 1200 and below 900. 

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This may sound silly but did you check the oil in that motor? I have had cars come in overfull of oil and has caused a low rpm vibration. Crank slapping to much oil around.

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11 hours ago, mpm330 said:

It is the same in or out of gear.  Today was a really nice day so I went out for a long run and it ran great when above 1200 and below 900. 

If they pull the drive, then hopefully they have a bore scope that they can pass through the gimbel bearing and seal, and take a really close look at the coupler. I just used mine to go through a garboard drain plug and was able to identify the source of an oil leak on a Formula. Engine oil cooler o-ring failure in that case.  If bore scope results are inconclusive, next step for me would be to actually remove the gimbel bearing, and slide a surplus upper gear case input shaft directly into the coupler, enabling me to measure lateral deflection, and spline tooth backlash clearance directly without interfearence from the gimble bearing. If the metal coupler element has failed, then there should be ample visual evidence as the input shaft is steel, and the mating coupler spline is aluminum, but if the rubber vibration isolation damper element has failed, it will be harder to see unless it has been operated in a failed state for a very long period and the rubber has begun to shred. Again, good luck and if she needs a coupler opt for the beefy stainless model used on work boats and big block engines. Unit costs a bit more but labor is the same  Also, a good engine alignment needs to be checked at various points of engine rotation. It may be fine with the flywheel at 12:00, but the alignment tool may tighten up when the crankshaft is rotated through 6:00. The key is to split the difference and find the sweet spot where the tool slips in and out with little to no resistance through 360 degrees of rotation. If you can't find that happy place, then you either have a failed coupler, of something has happened to the transom plate mounting surface where the transom mounted rear engine mounts are no longer square to the bilge bottom mounted front engine mounts. Remember there is no adjustment for side to side deflection, just up and down. A proper alignment happens when the front of the engine is hung from above suspended along it's center axis and is floating is space. Engine is raised and lowered until alignment seems perfect, then rotated as described above. When the sweet spot is found, then, and only then are the front motor mount jam nuts brought up (lower) and down (upper) to the point where they contact the engine brackets. This method eliminates any possibility of side loading (twisting) of the engine block. If the transom has heaved, then you can see where all bets would be off. I only saw this once on a big vintage Sea Ray with a thick plywood transom that had suffered from freeze damage after water infiltration. I doubt you will see that issue on your ride.  W

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Problem solved! They checked alignment and it was dead on, u-joints were good. They replaced the gimble bearing with a Merc. bearing and vibration is gone. The mechanic had never seen this before. They had installed a Sierra bearing when they did all the maintenance last fall. He is going to send it back to Sierra to see what was wrong with it.

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Glad they found it.  I know that had to have you concerned . . . 

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10 hours ago, Mi3sons said:

Aftermarket junk.

 

Yea their "Bravo" water pumps are junk too. Bearing failures and leakage right out of the box. W

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The mechanic said the Merc bearing had a warranty of just one year, but the Sierra is a 2 year warranty. All made in China. Just glad that I have a mechanic that would work with me and took the time to check it out. The guys here at my marina are great and one of the reasons that I keep my boat there. 

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