prop advice

[betty boop]

and the prop issue continues to a new post.

Ive fitted a new 14.25 x 19P ali prop exact match for the original prop but I now have a whining/high pitch hum on low revs. virabrations have subsided but been taken over by a noise I would describe as similar too running a finger around the top of crystal glass. Quite bizarra.

out of the water she spins fine with no noises. Im yet to dig deep into any causes but wondering if anyone has a thought?

[BruceK]

When I took my Alpha leg apart to replace the yoke in the upper gearbox I rebuilt her using all the shims used previously. I'll be brutally frank here but the engineering on these things suck big time and that's not limited to Mercruiser either. Volvo are equally bad. Anyway the shims had expanded somewhat, slight corrosion etc meaning the back lash was too tight. Caused the teeth to mesh together too tightly and gave off a similar grumble squeal when under load. Not dissimilar to shot roller bearings under load.

Has any work been done to the leg that would require it to be reshimmed? Particularly a new UJ yoke during a gimbal bearing / bellows change? Or has the top cap been taken off and not retorqued on properly causing the taper bearing to be too tight? Often these bearings get changed but not the race on the cap because getting the race out is a right PITA and then to shim it more so. I've also known people to remove the topcap to check oil. That top roller bearing is also the first to go if oil levels drop or you get milkshake.

[betty boop]

When I took my Alpha leg apart to replace the yoke in the upper gearbox I rebuilt her using all the shims used previously. I'll be brutally frank here but the engineering on these things suck big time and that's not limited to Mercruiser either. Volvo are equally bad. Anyway the shims had expanded somewhat, slight corrosion etc meaning the back lash was too tight. Caused the teeth to mesh together too tightly and gave off a similar grumble squeal when under load. Not dissimilar to shot roller bearings under load.

Has any work been done to the leg that would require it to be reshimmed? Particularly a new UJ yoke during a gimbal bearing / bellows change? Or has the top cap been taken off and not retorqued on properly causing the taper bearing to be too tight? Often these bearings get changed but not the race on the cap because getting the race out is a right PITA and then to shim it more so. I've also known people to remove the topcap to check oil. That top roller bearing is also the first to go if oil levels drop or you get milkshake.

no work that I know of, shes only done 79 hours in 8 years so I dont see the need to unless there was an issue. the Gimbal and bellows were all changed last year and theres been minimal use if any since then. corrosion sparks an interest though. The leg is anti fouled and has corrosion in places where I think the mercathode system hasnt been connected. (the lablled wiring for the system is not connected to anything - but yet to investigate this one.) I cant see any removal of the top cover but she was short of lube when on first run, yes i did think of a milkshake scenario but since topping up shes done 8hours or so and has no movement in lube levels pointing to setting after the gimbal/bellow/impellor change last year with no use after. I did think may be the gimbal is not in properly but no idea what the symptoms would be. I think mostof these will only be clear on season end when the drive comes off.

[Ianfs]

Gimbal Bearing and UJ noise would be worse on full lock and are usually grumbling noises rather than a higher pitch.

Is the noise really loud or just in the background? Also is it definitely coming from the Sterndrive?

Lift the leg and spin the prop, is it smooth?

One more thing, you say it is heard at low revs, does it disappear when you build the revs and at what revs? Or is it that the noise cannot be heard at higher revs because of engine and wind noise?