Strange noise

[lighthousealarms]

I know trying to have someone identify an engine noise w/o hearing it is a long shot, but thought I would give it a try anyway.
Towards the end of 2008 I noticed a noise developing in the engine area, that seemed to be coming from the rear area. The only way to describe it is to say it sounds a bit like marbles in a metal coffee can being shaken rapidly. The noise is not constant, but comes and goes and is not very loud. It is not affected by engine rpms or whether the outdrive is in gear or not. I thought when it started that it might be in the outdrive, but saw nothing wrong when I did the yearly servicing that winter. I ran it all this year with the noise, and had no performance issues with the engine or outdrive. Both ran flawlessly. It seems to have gotten a bit louder here recently however. Being a bit of a perfectionist, I really want to identify this noise and fix whatever is causing it, even if it is not harming anything. The only clues I have that might help are that I can not hear it when I throttle up and when I throttle down from a run to an idle, the noise is not present until I have been idling a few minutes. Otherwise it is there all the time. I suspected an oil pressure issue from that last clue, but assuming the gauges are working correctly, pressure and water temps are good. The other change I have noticed is the exhaust risers seem warmer at idle than they use too. And I can feel what I think is the water running through them, but it is surging and is consistent with the noise. In other words when the noise occurs I feel the surging. Also, my wife says she thinks the sound is coming from the front area, so I am leaning now towards a circulating pump or pulley?? If anyone has any ideas please let me know. As always thanks for your help.

 

[QC]

Re: Strange noise

What engine? What drive package? Trailered? Can you run her in the driveway and duplicate?

My suggestion is to have somebody else help you pinpoint the source. You either need to find it or wait for it to show itself Sounds like it might be a loose exhaust flapper (rear), but the confusion between front and rear makes it hard to help much. I would also look for loose bracket connections for any accessories although some of what you note is not consistent with that.

 

[SuperNova]

Re: Strange noise

What engine? What drive package? Sounds like it might be a loose exhaust flapper (rear),.

I agree, but what happens on the flappers sometimes is the rubber that covers them wears off at the edges and you hear them tapping inside the exhaust horn. My boat does it, too. Sounds like detonation but it happens at idle. But we need to know details about the boat and engine.

 

[lighthousealarms]

Re: Strange noise

Sorry about that. It is a 1994 Rinker Fiesta V with a 7.4 Merc, Bravo II drive. Would exhaust flappers cause it to make that noise all the time other than after running it across the lake? That is probably the part that confuses me the most. I can not hear the noise after a run on the lake until I have been idling awhile again. For example, I enter a no wake zone after a long run to go back to my slip. It usually will not start making the noise until I am almost in the slip. Thanks for your help.

 

[Bt Doctur]

Re: Strange noise

Marbles in a coffee can is usually a bad gimbal bearing, gets louder when turned or tilted

 

[SuperNova]

Re: Strange noise

Sorry about that. It is a 1994 Rinker Fiesta V with a 7.4 Merc, Bravo II drive. Would exhaust flappers cause it to make that noise all the time other than after running it across the lake? That is probably the part that confuses me the most. I can not hear the noise after a run on the lake until I have been idling awhile again. For example, I enter a no wake zone after a long run to go back to my slip. It usually will not start making the noise until I am almost in the slip. Thanks for your help.

Yeah, it's kinda odd when the noise comes and goes, with the only constant being that it only does it at idle or just barely off idle. You have to understand how the flappers work. Once you take off the exhaust connector tubes that feed into the top of the exhaust horn the flaps are right there at the top of the horns and very visible. Push the pivot pin out and pull the flap out and look at the edges where it seals against the inside of the pipe, if the rubber is worn off then that's where your noise is coming from. Makes a very unique marbles in a coffee can sound that is not rythmic at all and goes away when idled up.

All the gimbal bearings I've seen failed made a growling noise with sometimes a noticeable low key vibration felt throughtout the boat.

A noise that gets worse when turning is usually the input shaft u-joints in my experience and its usually a clicking noise if they are loose, or accompanied by a jump in the steering if they are rusted tight.