Unsolved Yanmar Groaning between 1800 & 2300 RPM

[Bill Meyer]

Re: Hunter Legend 37 (88) 3HM35F Yanmar Last year the boat developed a groaning (R.R.R.R.) sound or a laboring sound between 1800 & 2300 RPM. Over 2300 the groaning either subsided or was not noticeable.The alignment was checked (O.K.) but the sound stayed with the boat. From my description, my mechanic felt it related to clutch cones in the transmission. This transmission does not operate with clutch cones. Earlier this season a rattling sound was added when throttle moved with short movements back/forth at under 2000 RPM. I could also create the same rattling sound when putting pressure on the shaft inside the boat.I have taken the following steps to isolate the problem:1. No noticeable engine vibration2. No boat vibration when standing at helm3. Transmission in neutral at 3500 RPM (boat and engine run smooth)4. Boat in reverse at 2100 RPM no groaning or rattling5. Checked the propeller (17x10 RH 2 Blade as per specs)6. Checked the shaft (1" s/s on the lathe - True)7. Replaced cutlass bearing8. Replaced Shaft flange and checked shaft lock bolts9. Removed transmission for visual check test under load10.Realigned shaft11.Checked engine mountsAll of the above did nothing to resolve the noise problem! Groaning at 2100 RPM + or - and rattling when moving the throttle forward/back.I am ready to take advice. Can anybody help?

 

[Paul Akers]

Something to try.

While sailing, put the trans into foward gear to make the shaft turn. Try to do it at the same speed that the 2000 rpm would generate. Maybe it will simulate the noise and then you will know, for sure, where it's coming from.Just a thought. Good Luck.P.S. I have a 1988 L37, also.

 

[Bill Meyer]

Thanks Paul

Thanks, Paul, for your advice. We will try it out and hope we learn something.

 

[Eric Lorgus]

Have you tried the new diesel forum?

Bill: You didn't mention the stuffing box? As these wear they require adjustment. Did you adjust the stuffing box before all this started? Could it be too tight or too loose?As for Paul's suggestion, if you're going to try to spin the entire drive train at 2000 RPM by putting it in gear while sailing, I'd be surprised if much happens, even with the compression levers opened. I think it would be more like trying to jump start a car with an automatic transmission. Fluid power behaves differently then direct drive.