gunrunnerjohn posted:I am not only sure, I'm very sure!
FWIW, it's also in the MTH documentation several places. It should be about the thickness of a dime at max. It is pretty close when you look at it. If it's more than about 1.2mm, it'll start missing counts, and as the RPM increases, it'll miss more.
The MTH tach sensor has the same specs as the sensor I use for my Chuff-Generator, and I spent a lot of time characterizing it. It actually peaks at about .8mm in sensitivity.
For others reading this post. I've run into a couple of engines that the MTH specs have to be pushed to the smaller limit for the tach to work correctly. The spacing was within the limits but the engines ran out of specs. On the one gauge versions for example, I had to grind down the truck tach mount holes to tighten the gap for correct speed matching.
BTW, I tried swapping out the actual tachs with brand new ones, changed the type of stripes, and even played with different boards on an O gauge engine. I couldn't establish why the tach didn't work correctly. I just found that it did work when the gap was set to the narrow part of the specs. I never have had to widen the gap yet.
On custom installs you may have to adjust the gap if you're not getting the expected results from stripe changes!
