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| | | | Joined: Apr 2011 Posts: 106 Wrench Fetcher | | Wrench Fetcher Joined: Apr 2011 Posts: 106 | I'm installing a VDO tachometer, a baisc one without an hour meter. I've got it all wired up, but there is something in the instructions about manually fine tuning it:
"Before your VDO Tachometer will function properly with your engine, you will need to configure it as shown in Diagram C (see below). the table at the top shows how to set the DIP switches for use with an ignition coil; the table at the bottom shows how to set the DIP switches when using the tachometer with an alternator. Note that manual fine tuning can be done using the potentiometer on the rear of the instrument. (See Diagram A). NOTE: This procedure should be done by an experienced mechanic ONLY, using a hand held reference tachometer. Fine calibration can be made between 30% and 100% using this fixed reference."
Can anyone explain what this means, and how it is done? Or is it even necessary? I don't care if it's slightly inaccurate. I won't be racing my truck or anything.
Thanks!
1940 Chevy 1/2 ton, 12 volt, 350/350th
| | | | | Joined: Jul 2008 Posts: 326 'Bolter | | 'Bolter Joined: Jul 2008 Posts: 326 | Steve;
I think the fine tuning is for the alternator set up. Some tachs can use the pulses from the alternator to calculate the RPM. For example this method can be used on diesels where there are no ignition pulses coming from distributor/coil. The pot let's you tweak the signal to coordinate the pulses to crankshaft RPM because the alternator is not generally turning at crankshaft speed. You should be good to go by hooking up to the ignition. There usually is a diagram for both conventional and electronic ignition systems. Good Luck
SimS | | | | | Joined: Apr 2011 Posts: 106 Wrench Fetcher | | Wrench Fetcher Joined: Apr 2011 Posts: 106 | Steve;
I think the fine tuning is for the alternator set up. Some tachs can use the pulses from the alternator to calculate the RPM. For example this method can be used on diesels where there are no ignition pulses coming from distributor/coil. The pot let's you tweak the signal to coordinate the pulses to crankshaft RPM because the alternator is not generally turning at crankshaft speed. You should be good to go by hooking up to the ignition. There usually is a diagram for both conventional and electronic ignition systems. Good Luck
SimS Okay, so with a typical points and condensor type ignition system, if I'm connecting the tach directly to the negative side of the coil, then I should be fine then? If it matters I'm using a 1970 350cid with a stock distributer and 3 wire alternator. Thanks!
1940 Chevy 1/2 ton, 12 volt, 350/350th
| | | | | Joined: Jul 2011 Posts: 15 New Guy | | New Guy Joined: Jul 2011 Posts: 15 | Steve, Most tachs will say that. as long as your dip switches are correct there should be no reason to manually calibrate the tach you are using. The setup is usually meant for non standard type setups. Your standard 350 will be find and your probably going to be within 100rpm of accurate if not dead on. I wouldnt worry about a calibration
Curtis Kershner
1959 GMC Apache (in progress)
| | | | | Joined: Oct 2006 Posts: 4,983 Master Gabster | | Master Gabster Joined: Oct 2006 Posts: 4,983 | Turn your engine off; if the needle sits on 0 it must be zeroed out. lol
~Jim
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