RV-6 Tach trouble

[Tango Mike]

First time poster, non-builder, seeks advice! IO-360 with vacuum pump, Van's tachometer and transducer, dual Electroair ignition. Tach reads normal at start up and at some point during flight (no consistent pattern) decides to indicate zero. Usually recovers prior to landing. Troubleshooting tips, anyone? TM

[Kyle Boatright]

Troubleshooting:

1) Pull the tach cable and verify that it hasn't broken. If it is broken, replace it.

2) Lubricate the cable while you have it out.

3) Go fly the airplane and see if the tach works properly.

4) If not, replace the tach. They are only about $90. I replaced mine last spring at ~450 hours.

[rvbuilder2002]

Originally Posted by Tango Mike

First time poster, non-builder, seeks advice! IO-360 with vacuum pump, Van's tachometer and transducer, dual Electroair ignition. Tach reads normal at start up and at some point during flight (no consistent pattern) decides to indicate zero. Usually recovers prior to landing. Troubleshooting tips, anyone? TM

One problem that occasionally shows up on Van's tach is that the cable doesn't engage very deep into the tach drive on the back of the engine.
This may be related to the drive that is installed in a particular engine, the length of the cable, a combination of multiple things...who knows.

Because the cable is made of spiral wound wire, it will tend to screw itself towards the tach generator. This can cause the squared off end of the cable to only engage in the tach drive very slightly (as little as a 1/16 ")
after a while the squared end will wear allowing the cable to spin in the tach drive hole.

Check the condition of the squared end of the cable. If needed, you can add some spacer washers to the tach generator end of the cable to keep the cable pushed further out in the housing so that it is better engaged in the engine.