It turns out that my sending unit for the tach was an option (according to Volvo). The usual model got its signal from the alternator. Mine senses the teeth going past magnetically. They told me to count the teeth on the gear where the sensor is located. That wasn't real practical. I looked in the shop manual and there is a gear between the crank and cam that is about where the sensor is. It looks to have 21 teeth. I adjusted the tach according to the read out on a mechanical tach that I borrowed from a friend. 21 pulses per revolution appears to be the correct value. I checked the electric against the mechanical from idle up to 2000 rpm. I'm within 50-75 rpms, with the electric reading that much higher than the mechanical.
It's in and operating just in time for heading off to the annual Lake Michigan Cape Dory Owners Association Rondi in Sheboygan, WI this upcoming weekend. Thanks to all the folks who took time to offer help. Truly the best people are found here.
Jerry Hammernik
Lion's Paw CD28 #34
dauntles@execpc.com
Tachometer success!
Moderator: Jim Walsh