strange noise
 

Just trying to figure out a strange noise I can only hear when I am rinsing on the hose wirring noise almost like the gears in the out drive not meshing properly hard to describe.
Took the boat to a certified merc dealer its a 1998 7.4 bravo1 tryed u joints and upper bearings same noise so we swapped it out with a known quiet bravo and guess what same noise.
You can not hear it when you lift the engine hatch only when you stand behind the boat running on the hose. noise starts around 1000 rpm and gets louder with rpm.
Any ideas? Thanks in advance this is diving me crazy!

A bad Gimble Bearing makes that noise.

put in a new one then thought maybe it was bad from the factory so put a second one in still same noise.

Does it make the noise with the drive removed? easiest way to know if it is the drive.

With that old of a boat it could be U joints not aligned properly. If the rear engine mounts sag as they get old it will cause the U joints be not align. Yes I know that the alignment tool says it is perfect but it isn't. level the bottom of the boat and then insert the alignment tool and see if it is level with the bottom of the boat. They must be parallel. I had to raise the back mounts with shims and then raise the front mounts to get mine right.

Often you can get some noise from the engine coupler and the yoke during idle especially if you have not greased it in a while.
There are two grease fitting at the rear of the motor sticking out of the engine coupler, if that is in need of grease it will give you some noise.
When you solve the issue post what the problem was.
Big Boys Toys

thanks great suggestion you would like to think the merc dealer would have tried this but i will hit it with some grease my self the funny thing is even sitting in the engine compartment with a mechanics stethoscope on the bell housing you still can not hear the noise

not sure what you mean by rear mounts rear is attached to the bravo transom assembly only the front is adjustable can what you are describing happen with this set up?

The rear mounts are built into the engine bell housing at the back of the engine. They are rubberized and can sag over time. I had to put shims under mine to get it aligned. If an engine is properly aligned the alignment shaft will be parallel with the bottom of the boat. The gimbal bearing can pivot up and down and you can get the tool to go in even though the rear mounts have sagged. If the rear mounts sag then you won't get the alignment tool to go in so you lower the front of the engine to get the tool to line up. In the process you tipped the gimbal bearing down to get it to line up with the engine. The problem is that the front of the engine output yoke is tipped up at the front U joint and does not line up with the drive input shaft when the drive is in the neutral trim position. This causes side loading of the U joints and that side loading transfers to the engine coupling making it burn out.

thanks I will have it checked going back in this week also I just greased the coupler and guess what same noise this is getting crazy

what kind of exhaust are you running

Quick and quiet corsa

Could it be the internal flappers inside of the exhaust making the noise ?

I had corsa on mine, the internal flappers made a lot of noise at idle. It was a very loud ticking noise. It sounded like the valve train was coming apart. You can put your hand on the pipe at idle and feel the flappers are moving with the same pulse as the noises.

you certainly can hear the exhaust ticking but you can feel the noise when you put your hand on the outdrive top cap we have eliminated the possibility of it being in the outdrive by trying a known good outdrive and same noise I have used mechanic stethoscope to listen to exhaust bell housing cant hear it when I am in the engine compartment only at rear of boat on the hose at 100 rpms or higher and when I turn the wheel in either direction it gets worse
I know sounds like u joints but changed mine first brand new mercruiser parts no change then when we put the other outdrive on and same noise we confirmed it was not u joints
Thanks for all the comments guys this thing is driving me and my dealer crazy it is going back in this week we are going to check the rear mounts as a member has sugested

Does the noise go away when you put the drive in gear? If so you are hearing the shift fork cam bouncing up and down as the bump rings spin. That space will move up and down as the gears turn, causing the shift fork to bounce up and down. You can feel it and hear it. First time I heard it I was very concerned. Next time, not so much.. then I ignored it. Never had a problem with it. If you can find nothing else amiss, this is probably what you are hearing and feeling.
Hope that helps..
Dick

thats very interesting sound does change when put in gear but still there would this sound still be there even when we changed drives to a known quiet drive? I have tried playing with the shiftier while it was running not quite putting it in gear and the sound still remains constant

Try to run it with the drive off, if you have a water hose connection plumbed up. I don't think the noise your hearing is the flappers in the exhaust but one way to eliminate that noise is to take two broom handles and hold the flappers still while the engine is running. Keep us posted with what you find.

sounds like a plan thanks to everyone on the board for your help

Did you compare it to another boat connected to a water hose to see if they sound the same.

the noise was not there until I had the boat out a few times this is a new boat to me this year the merc dealer thought it was u joints that was also my first suspicion then we tried gimble bearing then we went through the upper new bearings still same noise thats when we tried a known quiet outdrive he had in the shop same noise
At this point I think I will have him run it with the outdrive off and recheck alignment not sure what else could be causing it

I suggested running it without the drive in post #4.

Sorry I missed that

Just informing you that it had been suggested earlier.

update greased the coupler same noise but after 2 times out noise seems to have diminished to quiet when wheel is straight and about the same when cut hard in either direction could this be the grease working its way in or is this just a coincidence?The other question is do I need a new coupler to completely fix this?

Cut hard in either direction is usually the gimble bearing. My IMHO. Smaller chance U-Joints, which typically make more noise up and down or if real wasted....all the time.

did new ujoints then we tried mercruser part new gimble bearing then tried another new one in case maybe it was bad since the noise is gone straight on this is some kind of improvement so not sure what is causing this to happen?

Did you ever check to see if the alignment tool was parallel to the bottom of the boat?

From what you say above that after greasing coupler it's a little quieter, maybe you might want to pull drive off and look at coupler with a flash light. Check to see if teeth have become warn and pointy or the teeth are full of dry grease and metal.

You requested that this post be deleted because your problem has been solved.
There is no reason to delete the thread. If we/mods deleted every thread where a tech problem was solved, nobody would ever learn anything.

Post whatever solved the problem. It may help somebody else later.

I agree with Griff, post your solution !
Several members have taken the time to respond, so you in turn should post what your solution was !
This web site is worthless unless you do your part , then many others will do a search on the same problem and fix their problem with minimal effort.
Boating in the high performance area is extremely costly, and unless you are a millionaire, most people on here do their own work , that is why this web site is so great !

Depending on transom angle this is not necessarily true. The alignment is checked to ensure the relation of the engine to the transom assembly and gimbal bearing is correct.

I had what may be the similar noise on my 32 regal with Bravo 3's. Warming it up at 1500 RPM's, with the drives turned, I could hear a rattling/knocking noise. Took it to my dealer, they replaced u-joints, gimble bearing, the noise was still there after they essentially threw parts at the problem (both of those items were less than 2 years old). Took it to another dealer, they knew the issue almost immediately. They removed the drive, verified alignment was on, greased the input shaft and replaced the two rubber o-rings on the input shaft. The service manager advised me the noise would probably be gone for 2 years or so. He was exactly right. The boat was silent for at least two years before it crept back in.

With the majority of boats it is true. The U joints have to be inline.