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Ronbill

Odd rattle or tinny vibration noise Volvo 4.3 GXi

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My Chap 196 SSi with Volvo Penta 4.3 GXi and SX-A just started to make a tinny rattling noise from behind the engine. The noise is not there when idling in neutral and seems to occur mainly when accelerating or driving in the 2000-3000 rpm range. Noise occurs when cruising straight and not necessarily when turning the steering wheel. To me, it sounds like a loose tin tag or metal bracket vibrating at certain rpm's. I even had my mechanic brother-in-law listen to the engine while running on the lake and he confirmed this is not a pulley, belt or obvious engine issue.

Could this be a possible outdrive issue?

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4 hours ago, Ronbill said:

My Chap 196 SSi with Volvo Penta 4.3 GXi and SX-A just started to make a tinny rattling noise from behind the engine. The noise is not there when idling in neutral and seems to occur mainly when accelerating or driving in the 2000-3000 rpm range. Noise occurs when cruising straight and not necessarily when turning the steering wheel. To me, it sounds like a loose tin tag or metal bracket vibrating at certain rpm's. I even had my mechanic brother-in-law listen to the engine while running on the lake and he confirmed this is not a pulley, belt or obvious engine issue.

Could this be a possible outdrive issue?

Hopefully it's just a loose clip to a hose that had one of its screws fall off and now it's tinkling off the engine at that RPM range and nothing more.  Look at anything and everything and make sure everything is tight first.

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18 hours ago, ColdOne said:

Gimbal bearing?

Yes that is one of my suspicions right now. Of course it is tough to hear noise outside of the transom when running the boat in the water. So I plan to run the engine out of water later this week to see if the noise is audible from behind the boat.

15 hours ago, Hatem said:

Hopefully it's just a loose clip to a hose that had one of its screws fall off and now it's tinkling off the engine at that RPM range and nothing more.  Look at anything and everything and make sure everything is tight first.

I really hope that is it but will need to look in behind to find it. This may take some work to find the source.

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18 hours ago, Ronbill said:

I really hope that is it but will need to look in behind to find it. This may take some work to find the source.

We will collectively will it with our combined telekinetics into being a ¢0.55 screw or bolt that needs either tightening or replacing. :)

If it only happens at 2000 & 3000 RPM and only during straight runs, conventional wisdom would suggest it's not something mechanical, but these are boats after all, so you can never say never.  But does it go away past 3000 rpm?  What about WOT or you just can't hear it beyond 3000?

The local mechanic took a boat on its trailer to the ramp once that he couldn't identify the problem/noise and tied it down really well Including stern straps and backed it down halfway into the water so drive was submerged but still connected to traler & truck.  He also had a F-350 dually but then they cranked the boat, opened the hatch and one guy would rev the engine while he stuck his head in and with a long screwdriver with the handle to his ear was trying to listen to different areas to identify where that noise was coming from. 

I was yacking it up with them and they were explaining that it was really the best way to do this since you can't really stick your head in the hatch while the boat is cruising on ocean water travelling at 20mph or whatever and holding a screwdriver with one end at your ear.  This looked like a much safer way to find a very difficult problem.  But you need to be very careful, especially with the screwdriver and all moving parts of the engine if you try that. 

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8 hours ago, Hatem said:

We will collectively will it with our combined telekinetics into being a ¢0.55 screw or bolt that needs either tightening or replacing. :)

If it only happens at 2000 & 3000 RPM and only during straight runs, conventional wisdom would suggest it's not something mechanical, but these are boats after all, so you can never say never.  But does it go away past 3000 rpm?  What about WOT or you just can't hear it beyond 3000?

The local mechanic took a boat on its trailer to the ramp once that he couldn't identify the problem/noise and tied it down really well Including stern straps and backed it down halfway into the water so drive was submerged but still connected to traler & truck.  He also had a F-350 dually but then they cranked the boat, opened the hatch and one guy would rev the engine while he stuck his head in and with a long screwdriver with the handle to his ear was trying to listen to different areas to identify where that noise was coming from. 

I was yacking it up with them and they were explaining that it was really the best way to do this since you can't really stick your head in the hatch while the boat is cruising on ocean water travelling at 20mph or whatever and holding a screwdriver with one end at your ear.  This looked like a much safer way to find a very difficult problem.  But you need to be very careful, especially with the screwdriver and all moving parts of the engine if you try that. 

It may very well be that I can't hear it beyond 3000-3500 rpm. I think i will have to try to get in behind the engine and feel around for anything loose. Maybe an extendable mirror will help.

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