loud unidentified noise

[Scienceguy]

Hi All,
My 406 with Volvo Penta engines, has suddenly started making terribly loud noises when in gear. It may be in both sides, but is minimal on the port. Increases of course at higher RPMs. The sound has two components: a grinding abrasive sound and a high pitched squeal. Can be heard on the bridge, but in the aft stateroom is incredible. So, took up the floorplate over the rear strut/cutlass bearing and sure enough BAM! mystery solved. Not so fast! Pulled the boat and there is absolutely NO PLAY in that bearing and it looks perfect. Same with the other side. Yard mechanics are totally puzzled.

Any thoughts?

[km1125]

and the gear oil looks good? I can see any sound generated in the driveline being transmitted to the hull through the strut, so the origin of the sound might be confusing.

[bud37]

Check yer engine serpentine belts and idler pulleys, they can make one heck of a racket if gone bad,

Never mind , I realize you said when in gear, sorry.......

[Scienceguy]

Check yer engine serpentine belts and idler pulleys, they can make one heck of a racket if gone bad,
Not in the engine because there is no sound when not in gear.

and the gear oil looks good? I can see any sound generated in the driveline being transmitted to the hull through the strut, so the origin of the sound might be confusing

Fluid was changed last year and looks and smells good. You bet it's confusing. I would have betted the farm on the cutlass bearing. Could it be that even if there's no play?

[Viper]

Have you checked shaft log temps? Are they drip-less logs?

Any notable vibration?

Did this happen while underway or was it fine up until shut down one day and then happened at the very beginning of the next time you started the engines? If it happened while underway, what were the conditions; speed, fwd or reverse gear, shallow/deep, calm waters, any alarms, etc.

Isolate one engine from the other to see if it's both sides. Turn on only one engine at a time and put it in gear to see if you get the noise from both sides on their own.

Existing engine issues may be more apparent when under load/in gear and quieter in neutral. Can you post a serial number or the spec number of the Volvos?

[Viper]

Any update?