[C320-list] Tachometer Problem

[Scott Thompson]

I don't have my manual handy.  Is the sending unit adjustable?  It 
occurs to me that clearances between the flywheel gear teeth and sensor 
might be off on my boat if it is.  I've got erratic and low tach 
readings that I haven't been able to track down.


Robert E. Sloat wrote:
> 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

-- 
Scott Thompson
Surprise, #653