Yamaha 50D whirring noise

[Swell6111]

Hi all

I have a 1988 Yamaha 50D that makes a whirring noise at certain RPMs when underway. It seems to come and go at different RPMs but the frequency of the sound doesn't seem to change with RPMs.

I've linked two videos demonstrating the noise. Does anyone have any ideas as to what it could be?

The motor looks healthy, WOT reaches a bit over 35knts at around 5500RPM, cold starts usually need the choke and a little throttle for a few seconds but then idles down fine. The crank case was split in 2023 (unrelated to this noise) and there were no obvious problems.

First video (low throttle)
Second video (a bit higher throttle)

[ausnoelm]

Hi all

I have a 1988 Yamaha 50D that makes a whirring noise at certain RPMs when underway. It seems to come and go at different RPMs but the frequency of the sound doesn't seem to change with RPMs.

I've linked two videos demonstrating the noise. Does anyone have any ideas as to what it could be?

The motor looks healthy, WOT reaches a bit over 35knts at around 5500RPM, cold starts usually need the choke and a little throttle for a few seconds but then idles down fine. The crank case was split in 2023 (unrelated to this noise) and there were no obvious problems.

First video (low throttle)
Second video (a bit higher throttle)

Could possibly be the driveshaft bush/bearing?

[Swell6111]

Is that the one in the top of the lower unit (number 6 on this diagram? I took the boat out for the first time this year on Sunday and the noise is still present, if a little louder than it was last year. It makes a funny noise in neutral too, which goes when you put it in gear at idle.

[99yam40]

the crank shaft and drive shaft spin all the time when motor is running, so any bearing those ride in could make the noise