I want to measure the position of the crankshaft with my homemade car computer and compare it to the signal from the no. 1 spark plug so I can measure the engine timing while driving. I was thinking the best way to do this would be to use JB Weld and glue 2 magnets to either side of the harmonic balancer so there would be 1 magnet at the 0 degrees TDC and another 180 off. Then use a hall-effect switch mounted near the magnets. Of course, I would be getting 4 signals from my make-shift CPS for every signal from the no. 1 spark plug, but the firmware would have to account for that.

  • Does your harmonic balancer have a hall effect sensor anywhere on the perimeter? If so, magnets will possibly cause damage to the engine by throwing off the timing. – fred_dot_u Sep 9 '18 at 10:59
  • I forgot to mention: it's a 1977 Ford F150 so no, there is no other sensors nearby. – SpaceCowboy Sep 9 '18 at 11:05
  • If you get them exactly opposite each other then it will be fine - make sure they are the same mass... – Solar Mike Sep 9 '18 at 11:08
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    I would be VERY cautious about "glueing" anthing onto rotating parts of the engine - not because of the risk of unbalancing the engine if you attach equal and opposite masses, but because of the centripetal forces involved. If your sensor is about 1 inch off the rotation axis, and the shaft is doing 6000 RPM, the apparent weight of the sensor will be about 1000 times its actual weight. The force trying to pull a 1-ounce magnet off the shaft will be about 60 pounds, not one ounce. Is your glue good enough to handle that? – alephzero Sep 9 '18 at 11:31
  • @alephzero I did this years ago on an Audi to make the petrol engine rev counter work on a diesel engine. Simple trick is to stick the magnets to the INSIDE face of the pulley, then the forces are not acting to pull it off. Just have to orient the sensor... – Solar Mike Sep 9 '18 at 12:41

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