RPM Sensor Do Over (6)

 6 hours

Alright now that the engine is running I can see that my RPM sensor mounted next to the flywheel does not work very well.  My next best idea was to mount it behind the prop hub to sense the back side of the six prop bolts, so I will try that.

This is the area I'm thinking of:

I think I can fit a bracket there without interfering with the cowl.

Here's my first rough draft pattern:

Something like this:

Attempt number 2:

Next I started making it out of some 0.032" scrap.  I started at the bottom and worked my way toward the top, trimming and bending as I went to try and create what I had in mind.  The bottom mounting point is just an unused tapped M6 hole in the front of the engine case, and the top mounting points will be the forward two bolts on the oil breather plate.

This is pretty close to what I was going for, although I made it a bit too close to the bolts so there's not much room for adjustment!

Next I tested my new setup.  I wanted to sanity check the reading on the G3X, so I bought a $10 lawn mower tachometer and attached its sensor wire to one of the spark plug wires.

Then I just ran the wire through the fuel door and set it on the glareshield.

It works!  Here you can see how much more stable the RPM display is than before, and it matches the lawn mower tach as well.

Now that I know it works, I can improve my bracket.  The original was a little flexible, and too close to the prop bolts anyway.  I made a new one with 0.064" sheet, which is turned out nice and solid.  I made it slightly shorter too, so there's more room for adjustment on the sensor itself.  This is still the temporary prop, so I will have to adjust the sensor later I think.

I put the cowl on to make sure nothing interfered, and it's all good.  You can't even really see the bracket from the front so I definitely don't think it'll block any cooling airflow either.