Advice? - 5.0MPI/Bravo III Vibration

[Water U Lookin' At]

I've been chasing this vibration since last September. Thought it was engine related - replaced all wires, plugs, ignition coil, disributor cap, fuel filters, IAC, IAC air filter, cleaned flame arrestor, checked risers, checked engines on computers (they run within 5 RPMs of each other). Now I think it's stern drive related (although I had them both serviced along with having all the bellows, shift cables, and trim senders replaced) - props are being spun now to rule them out. If they're good, then I'm going to have the boat taken out of the water again to check shafts in the drives.

Anyone come across this before in this configuration? Any help is appreciated!

Eddie

 

[Stray Cat]

I suspect it is your engine to bravo alignment.

 

[JeffM]

Can you describe the vibration?

If the props on Bravo III drives are not aligned properly, they can cause vibration. The blades need to be aligned so that only one passes top dead center at a time.

Jeff

 

[skolbe]

Engine alignment - which can lead to bad engine coupler.

 

[Water U Lookin' At]

Thanks for the responses!

Strange thing is that I just had the drives serviced 2 weeks ago by very reputable local mechanics referred to me by my friends. The alignment should be included in that (maybe they just didn't get it right), especially after they replaced the gimbal bearing as part of all the bellows replacements. The props were aligned (one blade at 6 o'clock while the other is at 12 o'clock), but I'm having them checked for correct pitch to make sure they're balanced. I should get the props back tomorrow and I'll put them on if I do. I'll let you know what happens.

Eddie

 

[keokie]

I'm chasing a vibration problem on my 310 as well. It is on the port side. The problem is not noticeable until you get over about 1400 rpm. I also have lost about 150-200 rpm at WOT on that side.

I thought it was the drive, but the problem remains when you run the motor with the drive off. I have tried a number of things such as new plugs, compression test, dropping one cylinder at a time to verify all are firing, etc. I'll let you know when I find it. Please keep me apprised of your situation as well. Maybe we have the same problem.

 

[Water U Lookin' At]

Interesting. Please do keep me informed about your progress Keokie, and I'll do the same. I put the props back on, with no change in the vibration, even though the prop guy said that my props were a little out of balance.

One thing I notice is that when I put the engines in gear at idle speed they are not synchronized. At idle the needle in the sync gauge was dead center. Now the starboard engine lags the port engine. When they are both out of gear in idle speed, the vibrations from both engines are similar. It's only when the port engine goes into gear that I notice the issue. And it's noticeable in the helm seat, windshield, and hull, but not the engine. When underway, I lifted the hatch to see if the engine itself was noticeably vibrating, but it wasn't. So, I'm thinking the alignment or something drive related is off. It's just disconcerting because I just had all that drive service performed. Needless to say i'm bringing the boat back to the guys who worked on it. Luckily it's not deep into May yet!!

Eddie

 

[keokie]

My problem will manifest in neutral or in gear. The easiest way to notice is to simply bring the RPM above about 1500. It gets more noticeable as RPM increases. If you put both engines in neutral and rev them one at a time there is a clear difference between the port and starboard motors. The port motor is the one with the problem. And as I mentioned before. It exhibits the problem even with the drive removed.

Can you isolate to one side? Will it do it in neutral? Have you tried it with the drives removed?

I will be diving into mine again this weekend. I'll keep you posted.

 

[gerryb]

If you suspect a vibration in the engine or drive alignment, it is not a good idea to go WOT with it. Will do more damage and not assist with diagnosis process.

Sounds like a drive alignment problem to me in this case. Let us know what they find.

 

[Water U Lookin' At]

I can isolate my problem to the port side. In neutral, both engines vibrate a little, which I think is normal. It's only when in gear that I notice the vibes in the port engine. As the RPMs increase, the vibes are less noticeable.

I read something about u-joints being an issue. Here's a quote from a site I found - "With a stern drive, the next thing to check are the universal joints. These need to move up and down for proper trim and to rotate freely to smoothly transfer the power from the engine to the drive. If one of the joints is stiff or unable to move through its full operating range, it will cause vibration." Here's the whole article -

http://www.boatingmag.com/article.asp?article_id=73&section_id=3

My mechanics assured me that the alignment is good, and that the engine is fine. The props are fine, and I never hit anything with the stern drive. So, I'm thinking it might be the u-joint, at least in my case. We'll see.

I'm taking the boat back to the mechanics on Monday. Hopefully, they'll finish up next week! More next week.

Good luck with yours this weekend Keokie!

Eddie

 

[Dave S]

I don't have the answers to your problems, but there are a few things I will point out that may be of interest.

Whether your drive is in neutral or in gear, keep in mind the drive shaft is still spinning. So if you experience a vibration like keokie describes, you can be pretty certain it is drive line related whether it be u-joints, gimball bearing, alignment, or something else.

Also keep in mind that some B3s go thru what I call a vibration cycle where vibration is more noticable. On my 260DA I get a slight vibration at 2200-2500 RPM. It is bit annoying but not un-common at least on the newer 260DA. (I have been on two other 260DAs that did the same thing.)

Then of course there is the controversial issue of prop timing where you need to make sure sure your props are installed in a clover overlap position with the rear prop having one blade pointed toward the cavitation plate while the outer prop is installed with one blade straight down. If they are installed in this fashion it will keep blades from the outer and inner prop from passing under the cavitation plate at the same time thereby reducing turbulence. This caused a vibration for me on my previous 240DA before I re-installed the props in the fashion mentioned above. Whether your particular drive will vibrate or not if the props are not timed like this, I can't say. The only thing I know is it takes no additional effort to install them in the manner I described so why not do it that way to begin with?

Dave

 

[keokie]

There are many components to an outdrive that can cause vibration problems. I would suggest running the boat without the outdrive or switching them port to starboard and see if there is a difference.

Also, vibration can damge many components in both an outdrive and an engine, so the advice not to go to WOT is sound. In fact, I'm only running the motor when necessary for diagnosis.

I sure will be glad to solve this one.

 

[Water U Lookin' At]

FYI - Now they're saying it's the prop shaft that's bent, because that's the only thing not spinning when the boat is not in gear. Therefore, when the boat is in gear, and I feel the vibes, it must be from the shaft (already had props checked).

I talked with Mercruiser and they said it's possible to bend a prop shaft without bending the props. If the props come out of the water while coming off of a wave, and re-enter the water, the impact of the props onto the water could bend the prop shaft.

Soooooo, tomorrow I'm going to take the boat out of the water AGAIN ($250) and have them check the shafts. If they're bent, I'll have them reconditioned, which Mercruiser does not recommend. However, they also don't recommend reconditioning props, which I've had done with great success. I'd rather save the $800/shaft, pay for a $40 reconditioning, and take my chances.

More on this after I get the shafts back (I'm pretty confident the shafts will be the culprits)...

 

[beachcombersc]

FYI - Now they're saying it's the prop shaft that's bent, because that's the only thing not spinning when the boat is not in gear. Therefore, when the boat is in gear, and I feel the vibes, it must be from the shaft (already had props checked).

I talked with Mercruiser and they said it's possible to bend a prop shaft without bending the props. If the props come out of the water while coming off of a wave, and re-enter the water, the impact of the props onto the water could bend the prop shaft.

Soooooo, tomorrow I'm going to take the boat out of the water AGAIN ($250) and have them check the shafts. If they're bent, I'll have them reconditioned, which Mercruiser does not recommend. However, they also don't recommend reconditioning props, which I've had done with great success. I'd rather save the $800/shaft, pay for a $40 reconditioning, and take my chances.

)...

Its not bad logic to say that if it starts when in gear, that it must be after the gears. You must also take into consideration that when not in gear, there is no load on the system. This in itself can hide the true problem. Alignment, gimbals,and u joints in the drive is more likely your source.

As far as you getting that beast out of the water, you would have known that for sure. I find this hard to believe this was the fault.

I would bet that the shop will "find" some problems with the shafts. If you go in there saying, "I think my shafts need work", they will not talk you out of it...

Good luck!

 

[Water U Lookin' At]

Here's an update!

We measured the runout on the prop shafts, and they were fine.

They suggested that the vibration isn't that big a deal and that I could live with it for the summer. Since the boat was out of the water I told them to check the u-joints and they did see some flat spots in one of the u-joints from my port stern drive.

They're going to replace them all and I'll put the boat back in the water on Friday.

More to come this weekend. I'm hoping this fixes it, because if not, then it could be the coupler, which requires removing the engine from the boat to replace. That will be a job for next year if I even decide to do it...

Eddie

 

[Bobby LaChance]

I'm dealing with the same issues. I had the seals in the outdrive replaced and now I have a vibration at 1100RPM. Mechanic now thinks that the bearings may be causing this problem. The next move is to remove the outdrive and inspect the bearings. I will be taking that day off and provide a second set of eyes as he digs into the bearings just to keep him honest. Whenever I have work done to the engine or outdrive I insist on a sea trial as I still hold the check.

 

[Water U Lookin' At]

Bobby,

Do you mean the bearings for the prop shaft? I asked them about those too, and they said if any of the bearings or gears were going bad, you would see metal shavings on the magnetic drain plug of the drive when changing the gear oil.

I didn't know about the magnetic drain plug until that point. Since then I've heard of many installations that have that magnetic drain plug. Pretty smart invention.

Good luck with your issue and please follow up here. I'm supposed to put my boat in the water today, but it's raining pretty heavy here. I'll follow up soon.

Eddie

 

[Water U Lookin' At]

Well, I put the boat back in the water last Friday and I still have vibes. I'm starting to think it's an engine problem. My temp gauge doesn't come up until I'm underway for a while. So, I think my thermostat or cold temp sensor might be bad. I'm checking that tomorrow.

Eddie

 

[Water U Lookin' At]

Well, as I thought in the first place, my problem has been a faulty wire or wire harness. We hooked the port engine to a computer and couldn't see a lot of data. So, the mechanic did a "wiggle test" and the data appeared. At the same time, the engine smoothed out, the gas smell went away, and the vibration was gone.

So, I took it for a ride and the vibes came back. I took the boat back and asked them how they fix intermittent wiring issues and they called the Mercruiser rep to come and look at it. They're not savvy when it comes to wiring and computer issues. The only thing is that i have to wait for the rep to show up and I'll only have 1 day's notice as to when he'll show up. In the meantime, I'm going to see if I can see any wires with missing shielding or anytihng else obvious.

So, the saga continues, but at least we're narrowing it down. We just need a fix and we'll have resolved the most troubling issue to date.

Eddie

 

[douglee25]

Your first route would be to trace the harness on either end and clean all connections and or plugs by spraying some electrical contact cleaner and reseating them.

If that doesn't fix it, try the wiggle test again to see if you can trace a specific area on the harness where the problem seems to go away. Once you can localize the area, then you have to dig deeper to see if you can locate a specific wire that causes the problem to go away when the wiggle test is performed. If both ends of the harness are open, an Ohm meter can help locate the problem as well.

If the wiggle test confirms the problem lies at a plug, the connection is either dirty or the male/female pin/socket combo are to blame. Replace as necessary. Sometimes wiring can be a pain in the a$$.

Doug