I recently experienced a failure of the upper gear case on my
MerCruiser I/O. After the shop replaced the upper gear case and put
the boat back in our slip, I took the boat out and noticed a prominant
"harmonic whining" sound coming from the lower unit when in gear. I
inquired and was told that that is the gears meshing, and the newer
the gearings, the louder the whine can be (no, my wife wasn't in the
boat). They state it is common to I/O configurations, and may be
especially loud on new boats. All I know is my old lower unit didn't
make any appreciable sound.

Is the mechanic correct?

Thanks.

Coff

Coff,

All I can tell you is that my Mercruiser Alpha 1 has had gear whine at certain speeds since it was
new (1997), and it doesn't seem to have affected the performance or longevity any. It mainly whines
at low speeds such as when you are slowing down to come off step, or are cruising at minimal planing
speed. For my boat this means around 2200 - 2500 RPM. If you either pull it back to idle, or
increase the RPM, the whine goes away.

If yours is whining at all power settings, then I would suspect that something is wrong, and it
needs to be looked at by a different mechanic.

Good luck with it,

Don W.

Coff wrote:
I recently experienced a failure of the upper gear case on my
MerCruiser I/O. After the shop replaced the upper gear case and put
the boat back in our slip, I took the boat out and noticed a prominant
"harmonic whining" sound coming from the lower unit when in gear. I
inquired and was told that that is the gears meshing, and the newer
the gearings, the louder the whine can be (no, my wife wasn't in the
boat). They state it is common to I/O configurations, and may be
especially loud on new boats. All I know is my old lower unit didn't
make any appreciable sound.

Is the mechanic correct?

Thanks.

Coff

Just had my alpha 1 rebuild after top gear failure. The mechanic suggested
we run the engine with the muffs on while the boat was still on the trailer.
Noticed some whine, mechanic said it was normal due to the new gears. With
the boat in the water after several hours of use the whine went away.


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