The International Cessna 170 Association

I have had now 2 incidences where the replacement of a mechanical engine tacho with a Electronics International tacho gauge has caused grief or misunderstanding. These 2 owners were replacing their tacho as per the E.I.,s manual. I to had issues fitting it or better getting it to work with my aircraft. There are these isolators to fit on the P lead or to the P lead. to stabilise the the readings . The manual gives advice if there is Bendix Mags fitted . Nothing about Slick Mags . The manual goes on about using a combination of isolators to get a proper reading . It’s suggested to start with a 79 om lead. then progress on. I did much research and talked to the factory but didn’t get any results . so to cut a long story short , i use Slick 4371 mags on a O-360 lycoming engine . I have fitted 49om leads and the system works perfectly. The readings are rock steady and dead accurate . The engine must be running and at idle to get a reading . I think this is to protect the tacho when the mags have impulse couplings or shower of sparks set up.