I fitted a Tiny Tach (a search will turn up the details) to my 722. Dead easy to fit and does not need to be wired in, as it will work on a 9v battery, if required. It works very well, sited it in the engine bay; it may not suit if you require a control panel mounted display.
My fishing vessel uses a digital push bike speedo, $30. Internal watch battery lasts about 3 years. Magnetic pick up is mounted on the front pulley of a 6 cylinder Gardner. Speedo is on the dash. Calibrated at K/hr and 24 inch wheel it gives the rpm but with the decimal place in the wrong spot.
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My fishing vessel uses a digital push bike speedo, $30. Internal watch battery lasts about 3 years. Magnetic pick up is mounted on the front pulley of a 6 cylinder Gardner. Speedo is on the dash. Calibrated at K/hr and 24 inch wheel it gives the rpm but with the decimal place in the wrong spot.
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No experience with Tiny Tach, but from the info, it looks an efficient solution. That said, in order to tune my now defunct Kiwiprop, I had installed a wired bicycle speedometer on the prop shaft, as well as a wireless one on the engine. It was great to make up rpm charts versus knots. Total cost: about 15 EUROS for the lot in the sales.
Fit a tiny tach.3 good reasons,
1 Digital read out.(Analogue 0-8000 rpm are useless when you are only doing 1000rpm)
2 No excuse for missing oil changes when hours are up.
3 No excuse for not logging daily hours run in log book
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Disused rather than defunct, sorry. The dealer had modified it twice after the reverse mechanism packed up mid-season (see earlier threads). He was kind enough to take it back since. Since you can adjust the prop pitch quite easily, it was interesting to study the effect of various settings. This was the original setting:
Y= paddlewheel log reading, X= RPM shaft
The shaft is of martensitic SS, and so the magnet just sticks on !