Re: [OMC-Boats] Prop spinning in Nuetral?

On Tue, 11 Aug 2009, Nexi wrote:
> Took a next step to make sure the engine runs. Started her up with the
> drive up, someone said this was ok as long as the boat is in nuetral.
> Oddly enough the prop is spinning while in neutral. Shouldn't the prop be
> at a stand still during neutral?

With these drives, it's normal for props to spin a little bit in neutral.
Even though the drive gears aren't engaged, they're still spinning on the
shaft, so friction is enough to cause some prop rotation.

 To understand what's going on, think of a bevel gear on a vertical shaft
coming down from the upper unit. The prop shaft is horizontal and has two
bevel gears it that can rotate freely on the shaft - both are engaged to
the vertical bevel gear, one on the "front" spinning "forward", and one on
the "back" spinning backwards. This happens in forward, in neutral, and
in reverse - all the gears are always spinning. When you put the drive
into gear, one of these gears is "engaged" by "locking" it on the prop
shaft, so the prop begins spinning. Thus, it is conceivably possible that
the prop might turn forward, backwards, or not at all, in neutral,
depending on which gear has the most friction with the prop shaft (probably
which bearing is in the worst shape).

The rotation might be fast, but there's no torque behind it. Push a stick
against the prop and you'll see that it stops immediately (I won't suggest
using your foot, though that's what I always do). Try this in gear and the
stick will be broken or thrown out, or it'll break your drive (i.e. don't
try it in gear). In the water, viscosity and friction are usually enough
to stop this from happening, though I have seen props spinning in neutral
before.

Also be sure you aren't running it *AT ALL* without a hose connected, as
you will rapidly burn up the water pump if there is no water in the
outdrive.

Ethan

-- 
<a href="http://www.engr.wisc.edu/~brodskye/"> Ethan Brodsky </a>