[C320-list] Tachometer Problem

[Melissa&Larry Leibman]

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