[C320-list] Vibrations at certain RPM Range

[John Meyers]

Starting about 3 weeks ago the boat is making a loud racket when the engine
is revving between 1500 and 2000 rpm. mostly in the rear of the boat but I
cannot pinpoint the source. This occurs both in gear and in neutral so not
suspecting shaft alignment. I suspect that it is some harmonic thing. All
motor mounts look good and solid and well attached with over a quarter inch
between the metal parts. I have check both feeling and/or removed just
about every thing in the lockers like spare prop, spare anchor, propane
tank, and other items that might be shaking while the noise is occurring. I
have felt the fuel tank and engine and nothing feels different than when
the noise is not noticeable. I have even gone below the boat and felt the
shaft prop cutlass, rudder and all seem solid. The shaft and cutlass
bearing were replaced a couple years ago. I have checked the steering
mechanism.

To explain the noise/clatter it sounds like a loose hatch, door, or
equipment is shaking.

At low revs and higher revs the noise is not there.

Has anyone ever had this problem or know someone that has/had this problem?

Thanks for all your help in past, present, and future. I rely on the
questions and answers this list provides.

John Meyers
Wind Chime 1997 #406
Muskegon, MI