[C320-list] Tachometer Problem

[Robert E. Sloat]

James-A few years ago I had a problem with the tachometer giving strange 
readings like yours on my hull 894 (2002) with a Yanmar 3GM30F.  The problem 
was a little corrosion on the electrical plug connection near the magnetic 
pickup sensor for the tachometer.  The sensor is located near the flywheel 
at the top of the bell housing and the connection connects the tachometer to 
the sensor.

Since your problem seems to go away when the engine heats up it may be a 
combination of corrosion and moisture in the above electrical plug 
connection.

My solution was to take the electrical plug connection near the tachometer 
sensor apart and clean it off and plug things back together.  No problem 
thereafter.  It is interesting that my boat was commissioned new in 2002 and 
has spent its entire life on fresh water Lake Michigan.  The corrosion on 
the plug occurred after only 3 seasons.

Bob Sloat
Savannah Hull 894

----- Original Message ----- 
From: "Jamie Pett" <JPett at JP2ARCHITECTS.COM>
To: <C320-List at Catalina320.com>
Sent: Monday, July 06, 2009 4:08 PM
Subject: [C320-list] (no subject)




List - I had an odd tachometer anomaly this weekend and wondered if
anyone can shed some light ?



While motoring home I was monitoring the tach - always try to run at
3100 -3200 rpm which I understand is correct cruising for my motor-
Yanmar engine.  The tach would be reading 3100, and with no noticeable
change in the motor sound / speed etc. would drop to 2800 or so.  Once
or twice it jumped up to like 3400, and I found myself throttling down,
then my speed seemed slow.  ( To make matters worse, my speedo is not
working, and sender is not fouled - guess the sending unit went bad ? So
I am relying on gps for speed which jumps around a bit.)



Does the tach. Run off the alternator ?  Could the problem be a belt ?



Any thoughts on why this would happen ?



After running for 20-30 minutes, I go the rpms settled at 3100 and
stayed there steady all the way the home - 2 plus hours into Sunday's
non-existent wind.





Any insights appreciated -





James Pett

'Bella Luna' #614