Tachometer problem

[yachtsmanbill]

I will check all the above. Thanks! I have a drive/generator from a 6-71, but if I am not mistaken that drove off the cam balancer. (?) ws

[Genesis]

I've seen drives off the cam balancer before but they're not all that common on boats. Detroit also makes a drive that can go on any of the accessory drive ports on the geartrain - but when Allison gears are on the boat the Vickers pump has a convenient place to screw in the adapter and that seems to be the most common configuration I've seen on Detroits w/Allisons.

Basically all of the tach adapters that have a 90 degree output are subject to the wear and lockup problem that shears the stub driveshaft. The straight drive adapters off the geartrain are not, because they don't have that worm gear in them. If you pull it off and find the stub shaft sheared, and find that the place the stub shaft goes into in the adapter has play in it, don't bother replacing the shaft by itself - it'll just lock up and shear again....