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  OMC Trim Gauge Calibration

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Author Topic:   OMC Trim Gauge Calibration
jimh posted 10-02-2006 10:09 PM ET (US)   Profile for jimh   Send Email to jimh  
The trim gauge sender on my 1992 Evinrude V6 outboard was calibrated in such a way that most of the time the position indication showed up on the lower one-quarter of the gauge's range. After doing some reading in my OEM maintenance manual, I found that the sender mounting had some room for movement in order to calibrate the gauge. I took advantage of this to change the sender's mounting in order to move the reading of the gauge into a more favorable portion of the indicator dial.

The results may be somewhat more psychological than actual. Most of the time I was running the engine trim in the extreme lower end of the range. Now, with the re-calibration, my normal setting should move up closer to the center of the TRIM range marked on the gauge dial. At a minimum, this will make me feel like I have the engine running at a better trim, and it will also give me more resolution (due to better dial gradations in that portion of the scale) of where the trim is set.

The calibration is also subject to two other variables:

--the voltage supplied (via the VIOLET or RUN lead from the ignition switch)

--the resistance of a series resistor mounted on the meter terminals

It may be possible to improve the gauge's accuracy and range by improving these two variables. I may experiment with a small voltage regulator to more closely control the voltage to the gauge. For example, a 12-volt regulator chip could be added. This would remove any variation of the gauge reading caused by changes in battery voltage.

By adding a variable resistor in parallel with the fixed resistor on the trim gauge, it should be possible to tweak the dial readings to get them precisely where you want them in relation to the dial face calibration marks.

bsmotril posted 10-03-2006 07:48 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Just FYI, the Merc trim senders can be calibrated the same way. The sender has two mounting screws 180 degrees apart. One is slotted, so the sender can pivot around the fixed screw to move the gauge needle's position for a normal engine trim setting.
BillS
jimh posted 10-04-2006 10:52 PM ET (US)     Profile for jimh  Send Email to jimh     
Bill--It sounds like the Mercury trim sender is set up in a similar manner. The OMC sender has a slot at one screw, just as you described. Thanks for the information.
btb posted 10-07-2006 11:35 AM ET (US)     Profile for btb  Send Email to btb     
I recently calibrated my trim sender - the Yamaha display has some numbers going from 1 at the bottom to 5 at the top, so I adjusted the sender so the display showed a 3 (mid-range) with the motor trimmed parallel to the bottom of the boat.

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