[C320-list] motor mounts

[Robert E. Sloat]

Your new propeller may be too far aft on the propeller shaft.  I was told by
my Autoprop dealer that the maximum distance from the front of the propeller
hub to the strut should be no more than 1.5 inches.  When I installed my
Autoprop, the installed distance was at 1.5 inches.  Your flex coupling
probably added one inch to this distance from the OEM propeller to the strut
and I assume the Gori is heavier than the OEM propeller you replaced which
may cause the shaft to wobble from possible extra weight farther aft on the
propeller shaft.  Unfortunately, you may have to do the measurement checking
on the tarmac.

Some folks talk about replacing the brass OEM propeller shaft with 
stainless.  They say the latter has less flex.  I don't know.

When I installed my Autoprop propeller it seemed heavier than the OEM 3 
blade propeller and I should have weighed both but
didn't.  One season and no increased vibration over the OEM propeller.  The 
one spot on engine RPM where a little more vibration was present before the 
new propeller was installed moved to a a slightly different RPM.

Check with Gori to see if the 1.5 inches is critical for their propeller and
if the over pitching problem can cause vibration which I doubt.

Bob Sloat
Savannah Hull #894

----- Original Message ----- 
From: "Pat Moriarty" <patm at psiurethanes.com>
To: <c320-list at catalina320.com>
Sent: Thursday, July 26, 2007 9:01 AM
Subject: [C320-list] motor mounts


> Hello out there does anyone have any hints on this problem?
>
> I have switched from the 3 blade fixed to a Gori 2 blade folding and
> picked up lots of vibration. In trying to sort it out engine mounts came
> up and while underway I checked the shaft and sure enough there is lots of
> engine shake and shaft wobble. Question is since it did not exist before
> (it was so smooth before it was like electric) is the prop shaking the
> engine or the engine shaking the shaft. How do you test the motor mounts?
> I also have a flex coupling so shaft alignment is not as straight forward
> as standard and not as important. As found by users in the past Gori also
> over pitched this prop, I get hull speed at 2500 and can not get 3000 RPM
> out of the Perkins.
>
> Pat #130
>
> Pat Moriarty
> PSI Urethanes Inc
> PH: 800-888-5156  Fax: 512-837-8733
> Please visit our web site at
> www.psiurethanes.com
>
>