F30 lower unit makes rattling noise

[Marco Holland]

Hi,

I recently bought and installed a new F30 on my fishing boat. When making the first dry testrun (using a motor flusher) the motor run fine. But when putting it in forward or backward gear the lower unit makes a rattling (metallisc) noise at idle speed. when increasing the rpm's the noise goes away.

I went back to the Yamaha dealer who at first found the noise not normal. He opened and inspected the gear parts but could not locate te problem. He had to turn to the Yamaha distributor for assistance so I left the boat and motor with him. Yesterday he told me Yamaha had provided a new lower unit assy which he replaced with the one on my outboard. But the noise was still there. Yamaha conluded that the noise is caused by backlash in the gearing and is normal when the outboard is in dry run with the propeller installed. Their story is that when run in the water the propeller gets resistance from the water and the rattling sound will not be there. I haven't tried it yet but for me it sounds credible but I still not feel confident with it.

Can anyone confirm the explination of Yamaha before I start using te outboard?

Thanks for your help!

Regards,

Marco

[rodbolt17]

just run the dang thing.

its totally normal out of the water for lash , which you MUST have, to rattle.

think man THINK.
even though your ears and the tach doesn't show it.
that crankshaft accelerates and decelerates some everytime a piston fires on compression then slows on ex.

the prop due to newtons laws speeds up then tries to slow down with the crank.

see what I am saying?

[Marco Holland]

Thanks Rodbolt. I do not have much experience with outboards but I understand what you're saying. I'am going the run the thing.

greets, Marco.

[rodbolt17]

its called prop chatter.
gets worse with stainless steel props.
the fwd,rev and pinion gear all rotate with the crankshaft.
the clutch dog that slides on the propshaft will disengauge and re engauge the gear dogs as the crank speed changes.
this typically goes away above about 900 RPM or if the prop stays loaded.

the F150 is nasty with certain props.

[Marco Holland]

Hi Rodbolt17,

Do you think it is harmfull? Offcourse its not often that the motor runs when out of the water. But when so schould I avoid putting it in gear?

Thanks, Marco

[rodbolt17]

like the F150 propchatter its simply annoying.
its not a real bright idea to EVER engage a gear with a prop on.
spinning props can and will do nasty things to you,pets and hoses.