300CBi Rotor RPM needle split

[Heliboss]

Rotor RPM needle splits and bounces/oscillates intermittently. Happened maybe three or four times in a two hour flight. Straight and level flight Engine RPM stays steady in the green. Any Ideas as to what may cause this? Just a bad gauge??

[RagMan]

Sensor gone bad? Possibility of a bad gauge, but I'd count on a sensor going out before a gauge does. Just my 2 cents

[clay]

your rpm needles are driven by cables, if they are for some reason winding up tight inside the plastic sheething (sp?) and then releasing, then it will make the guage hop around like that. could be the cables going bad.

[heli.pilot]

your rpm needles are driven by cables, if they are for some reason winding up tight inside the plastic sheething (sp?) and then releasing, then it will make the guage hop around like that. could be the cables going bad.

I had a car, years ago, that the speedometer did the exact same thing. I changed the cable as you're suggesting and never had the problem again. I think the cable or the sheathing had some damage somewhere along its length and the two would snag every once in a while - showing as a "bouncing" needle on my speedometer.

[PhotoFlyer]

It usually indicates the tach cables need to be lubricated and/or replaced. However, there are some ships that will do this no matter what you do. There are 6 feet of spinning cable that twists and turns through the airframe, sometimes it is unavoidable.

[icepilot]

I agree, I have had this happen many times with the 300CB/Cbi. The cable needs to come out of the sleeve and be inspected. If it has no wear, Then re-lubricated. After that I would suspect the gauge. Good luck!