prop sync

[Frank]

I have about 125 hours on factory overhauled engines on my '65 PA-30. They've been nicely in sync, but about 100 RPM low, according to the analog gauge and confirmed by a handheld digital gizmo. I asked my mechanic to turn up the RPM on the governors, which he did - five turns of the screw, supposed to be 20 RPM per turn. Now the props sync nicely at redline at the start of the takeoff run, but by rotation speed the left has increased by 25 - 50 RPM, while the right stays put on redline.

There's the governor adjustment, and the pitch stop adjustment. What needs adjustment to make the left stay at 2700, rather than increase with airspeed?

Incidentally, these are IO-360's, Miller conversion... but that shouldn't make any difference in adjustment, I think.

[Kristin Winter]

Sound like you have a governor problem. When was the last time they were overhauled?

[Frank]

Governors were overhauled at the same time as the engines, about 125 hours ago. Doubt they're bad...

[N3322G]

By any chance have you noticed it being difficult to sync or keep in sync in cruise? In the past this has been an indicator that the dome pressure is not correct for us.

I have also found the gauge is not always the best indicator of prop speed. I have my husband fly and from the right seat I use a Hartzell strobe to check the RPMs at 2700 and 2400 while aloft. When the engines and governors were overhauled a few years back, it took a couple of iterations to get things back to being happy.

[Frank]

Thanks for the feedback. But no, no problem keeping the props in synch. And yes, we did check the rpm with a strobe... it agreed exactly with the tach in the plane. It's obvious, of course, when one goes out of synch.

[N3322G]

Best of luck - let us know when you solve the problem so we can all learn. Thanks.