Re: [OMC-Boats] Need help with Props, Thrust Washers 1970 Sportsman

A washer's primary job is to spread load over a larger surface area to
prevent localized loads from exceeding materials limits. Fairly significant
impact loads can be generated when the drive is engaged (forward or
reverse). In these cases, the thrust washer's job it to take very high
localized loads from the pin (a theoretical line contact about 1/4" long and
infinitely thin) and distribute them over a larger surface area on the prop.
(You probably know this, but you always want to spread loads over the
largest possible area to minimize the pressue (i.e. lbs per square inch) --
think about snow shoes.) The washer is made from a material more forgiving
to these loads whereas the prop is made from fairly brittle aluminum. The
failure mode I would expect to see without the washer is for stress cracks
to appear where the pin contacts the prop. These would appear over time and
eventually could propogate to the point of prop failure, but that would take
awhile and you'd most likely notice noise or vibration and catch the problem
before the prop completely failed. It does look like you have a little wear
from the end of the pin striking the prop (caused by the extra gap due to
the missing washer), but if you don't see any surface cracks in the prop and
everything else looks good, I'd put it back together (with the washer, of
course) and not worry about it.

----- Original Message -----
From: "William R. Lindow, DMD" <williamlindow@...>
To: "Evinrude & Johnson Boats of the 1960's and 70's"
<omc-boats@...>
Sent: Sunday, June 07, 2009 8:56 PM
Subject: [OMC-Boats] Need help with Props, Thrust Washers 1970 Sportsman

> It appears that my prop has been running without a thrust washer.
> What damage could happen without it. My original OMC prop is pretty
> chewed up so I wanted to replace it. It is the white one in the
> pictures. What is the missing thrust washer supposed to do? The
> first prop I bought is a new Michigan prop 14x16 012092 that is
> supposed to fit however the back inside is different than the OMC
> prop. The next prop I bought is a Michigan prop 14x18 012093 PR 124
> and it looks similar on the inside but has two channels running
> through it which the original does not. Hopefully the pictures may
> help someone figure this out for me.
>
> Thanks,
>
> Bill
>
>
>
>
>
>

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Received on Sunday, 7 June 2009