I have the M-18 Universal diesel (500 hrs) on my Catalina 30. The other day I was adjusting my throttle linkage and took it off the throttle (stop) bar and was able to rev the engine to the max governor "stop" setting. My tach in the cockpit showed 2600 rpm, yet the manual states the max rated rpm is 3200 and cruising rpm is 2200 -2600. When I shut the engine down the needle in the tach will 7 out of 10 times settle at the 1,000 range. I have no clue as to how to check the rpm at the engine in order to make adjustment to the tach. I do see a small adjustment hole on the back of the tach. I believe the tach operates off the alternator through electrical pulse, so that would complicate matters without knowing how to get this right. How do you remedy this? Thanks Bob
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You probably have a bad gauge.
Most Gauges are milliamp meters adapted for a wide variety of uses and the plate on the front is calibrated for that use. Disconnect the gauge/meter from the circuit and see if it returns to zero. That would be the first step. If it does return to zero then the electronics that drives the meter is at fault. After that I am unable to guide you.
Most Gauges are milliamp meters adapted for a wide variety of uses and the plate on the front is calibrated for that use. Disconnect the gauge/meter from the circuit and see if it returns to zero. That would be the first step. If it does return to zero then the electronics that drives the meter is at fault. After that I am unable to guide you.
Electric Tachs
An electric tachometer is probably never going to settle down to a zero rpm indication when the engine is shut down, its the nature of the beast. There are a couple of reasons the tach could be "off" from actual RPM of the engine. First, if the pickup point is off the alternator, you could be dealing with some belt slippage, or, if the alternator is a replacement, the pulley size may be different. this would result in a different alternator RPM to Crankshaft RPM than in the original design. The "adjustment hole" in the back of the tach may be your remedy. It could be a simple matter of finding out if there is a small screw in that opening and tweaking the tach until the reading at idle matches that on a test instrument. The other possibility is that the tach itself is old and tired and its internal pickup is no responding completely, although 500 hours shouldn't be a problem. If you can get your hands on another tach and hook it up to the original tach connection, without too much effort, you could compare readings, that might tell you if the tach head itself is the culprit.
An electric tachometer is probably never going to settle down to a zero rpm indication when the engine is shut down, its the nature of the beast. There are a couple of reasons the tach could be "off" from actual RPM of the engine. First, if the pickup point is off the alternator, you could be dealing with some belt slippage, or, if the alternator is a replacement, the pulley size may be different. this would result in a different alternator RPM to Crankshaft RPM than in the original design. The "adjustment hole" in the back of the tach may be your remedy. It could be a simple matter of finding out if there is a small screw in that opening and tweaking the tach until the reading at idle matches that on a test instrument. The other possibility is that the tach itself is old and tired and its internal pickup is no responding completely, although 500 hours shouldn't be a problem. If you can get your hands on another tach and hook it up to the original tach connection, without too much effort, you could compare readings, that might tell you if the tach head itself is the culprit.
What I did
When I replaced my tach I borrowed a hand held mechcanical tach that you hold onto the front of the crank shaft and checked it. The new tach had switch's that you set for different applications I set it when the tach read 600 rpm cause thats what my engine idle is according to the manual and the mechcanical tach.
When I replaced my tach I borrowed a hand held mechcanical tach that you hold onto the front of the crank shaft and checked it. The new tach had switch's that you set for different applications I set it when the tach read 600 rpm cause thats what my engine idle is according to the manual and the mechcanical tach.
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