Problem syncing props - bad governor or RPM Indicator?

Fearless Tower

Touchdown! Greaser!
Joined
Jan 1, 2010
Messages
16,474
Location
Norfolk, VA
Display Name

Display name:
Fearless Tower
Went up in my favorite twin (BE-76) yesterday since the left engine was torn down and prop replaced (some unknown individual took the airplane uncheduled, had a prop strike and then parked it without telling anyone). Repairs are now complete and it is back online. I've got about 100 hrs in this particular plane, but yesterday I was having one hell of a time syncing the props - constantly trying to adjust the props and never seeming to be real smooth (never had a problem before the engine was worked on).

A couple of interesting things to note:

-Before the prop strike, the right engine would typically want to redline RPM on the T/O roll. Yesterday, when applying full power I noticed that it was the LEFT engine that was indicating 100-200 over red line. I pulled the power back to keep it below 2800 and continued the takeoff. Once airborne I did what I normally do - pulled the props back to set climb power using the left as the master - ie set the left on 2600 and adjusted (or tried to adjust) the right to match...best I could do to get them to sound synced was to pull the right back to where it was showing 200 RPM below the left.

-Went up again this morning and tried using the right as the master and adjusting the left to match. MUCH smoother this time and the props synced up much better using the right as the master, but when doing this, the left indicates aboout 100-150 RPM higher than the right. So, if you set the right for 2500, the left when synced shows 2600-2650.

All work was done to the left, no changes to the right side during repairs.

The RPM gauge is a single, dual indicating guage (two needles on a single RPM indicator). I'm thinking that there is a problem with the left indication. Anyone experienced a similar issue? Is there a good way to narrow it down and rule out a governor problem?
 
If you can sync them "by ear", then I'd guess the indicator is bad. If not, then it's the governor.

Syncing by ear is more accurate than by gauge anyway.
 
given that the change happened after the engine was worked on and not the instrument I would start looking for problems on the engine side.
 
If it's an electric tach then it could be the tach generator. Easiest way to check is to swap tach generators from right to left (if you don't have a spare one available).
 
given that the change happened after the engine was worked on and not the instrument I would start looking for problems on the engine side.

If it's an electric tach then it could be the tach generator. Easiest way to check is to swap tach generators from right to left (if you don't have a spare one available).

Makes sense....I'll pass it on to the owner.

Thanks!
 
If you synch by ear and the needles are different the problem is the indicator. A 150 rpm differential will make a heck of a racket.
True....what was interesting though was that using the left as the master and adjusting the right to match by ear, I was able to get close, but it never seemed quite right. It seemed like I was constantly adjusting the right. But when using the right as the master, I didn't seem to have the same problem.
 
I THINK you have mechanical tachs, so I'd suspect the gauge as the shafts tend to work or not. The only in-between I've seen is a jumpy reading.
 
Back
Top