[C320-list] Engine vibration at low RPM. 3GM30

[Jeff Hare]

Hi,

It depends.  Do you feel boat vibration, or are you just seeing the engine
"rocking" in its mounts?  If you feel the boat shuddering, then this is not
normal, and *usually* indicates that the idle is too low.  If the engine
"looks" like it's vibrating a lot in its mounts, that's probably ok as long
as the prop shaft isn't bouncing all over. Some shaft movement is to be
expected at idle however.

The engine is supposed to oscillate (rotate/rock side to side) in line with
the prop shaft.  (imagine the prop shaft extending through the engine and
out the front and attached to fixed mounts at both ends. The engine will
pivot side to side around this shaft, more so when at a low idle, and when
revved up, it should appear to be much more stationary).  The Yanmar rocks
quite a bit at idle, but gets more smooth as you increase the speed.  

So, if the tach reads 1000 and you feel the boat shuddering, the idle is too
low and your tachometer is probably reading a little high.  Increase the
idle by adjusting the governor (on the cable right below the engine mounted
fuel filter).  If the tach is correct and it only smooths out (stops
shuddering) at higher RPM, your engine mounts may be shot.  Another thing to
notice is if you rapidly back the throttle down to idle position and the
engine shudders or nearly stalls then again, your idle setting is too low.

Cheers!
-Jeff Hare
#809

-----Original Message-----
From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf
Of Graeme Clark
Sent: Wednesday, May 13, 2015 6:24 PM
To: c320-list at lists.catalina320.com
Subject: [C320-list] Engine vibration at low RPM. 3GM30

I used to share a 320 with a Westerbeke for four years but now have my very
own with a Yanmar 3GM30 Fitted new mounts over winter and had the shaft
aligned professionally. She runs sweet as a nut down to about 1000rpm and
then a pretty rough vibration starts up Is this normal for this engine? If
not, any suggestions as to likely cause?
Thanks
Graeme
#366, Jaskar
England

Sent from cell: please excuse typos etc.!