John said: A short in your tacho can take your primary to earth irrespective
of the existence of diodes and I am sure there are automotive examples that you may have not observed. Tiny Tachs are notoriously unreliable, And so the story goes that as many people as we have here on the net, we have experiences that reflect negatively on one type system or another, for virtually every part of the plane. I have never seen a tach drive short a coil down, but have seen starter rings that were chewed and damaged due to starter wear, and these would cause an erratic signal to your tooth counter system. No I am not referring to a Hall Effect switch. If going to the crank for a signal, I would use either the internal method found on many 4 and 6 cylinder GMs or the external mounted to the back of the balancer. MSD makes a universal kit for crank trigger that can be retrofitted onto virtually any engine. Every system will have its strengths and weaknesses. Some guys are using points due to simplicity and low voltage requirements. I find that medieval when systems like one netter is using, the motorcycle CD system (I believe Serge is, sorry if I got it wrong) that is very simple and very reliable. Everyone will have to find their own comfort level with the system they choose, and compromises made with each design. No system is 100% failsafe. Especially in aircraft where they typically do not shim starters and an experienced ear can hear the starter clashing in the ring gear, I would not run a tooth counter, unless you like the same unreliability you say the Tiny Tach has. Colin Rainey brokerpi...@bellsouth.net
