[C320-list] Tachometer Problem

[Robert E. Sloat]

Larry-Good pictures and what you have concluded matches the Yammer Service 
Manual for the 3GM30F.  The number of teeth on the ring gear for the 3GM30F 
is 97.  For the 3HM35 version of this engine which I think is the sail drive 
model, the number of teeth is 114.  According to the Manual, the basic 
tachometers and the sending units for for either ring gear are the same so 
the black dial looks like it is used for switching to either ring gear 
probably.  This is not shown in the Service Manual and it doesn't mention 
the calibration screw.

>From your pictures it is clear how to dial in a working the tachometer if it 
is off from actual RPMs measured at the crank shaft pulley.

 Bob Sloat
Savannah 894

----- Original Message ----- 
From: "Melissa&Larry Leibman" <theleibmans at verizon.net>
To: <c320-list at lists.catalina320.com>
Sent: Friday, July 10, 2009 8:14 PM
Subject: [C320-list] Tachometer Problem


Jamie,

You may have already rectified the tach issue but if not, I have been having 
the same behavior for several months. I finally got around to checking into 
it beginning at the tach sender on the instrument housing and working up to 
the tach itself. I've uploaded a few pictures at:

http://www.catalina320.com/mediagallery/album.php?aid=214&page=1

It appears at least on Easy Going that the problem was at the tachometer. If 
you check out the picture at the link below, there is a calibration 
adjustment on the left side of the picture but on the right side is a kind 
of blurry black dial adjustment. I believe that adjustment allows you to set 
the number of teeth in the pinion gear. From the labeling around the dial I 
expected it to have 3 positions. However, it just turns continuously with no 
obvious detents. As the engine was running I adjusted this dial and at 
certain points the tach would jump much like I would observe while running. 
I adjusted within the first range/position until the tach appeared to give a 
stable reading. I figured I would also need to adjust the calibration screw 
but when I rechecked the tach with a laser tach, the readings appeared to 
match within the precision of the tach in the cockpit. I then ran the engine 
at several rpm settings and all seemed to agree well with the
 laser tach. Previously my laser tach gave readings 100-400 rpm lower than 
the cockpit tach depending on the speed.

http://www.catalina320.com/mediagallery/media.php?f=0&sort=0&s=2009071017503760

I haven't had a chance to take the boat for a spin so I'm not certain if the 
problem is really solved but so far so good.

Larry