I’m having a vibration issue with the left engine on the Cessna T303. The vibration is most pronounced at high power settings. This engine is designed to be run at 2400 rpm from takeoff to touchdown and has been run that way for 1900 hours (it’s a derated Cont TSIO520 - 250HP). However, I have tried different rpm settings to no avail. Mounts are new, exhaust isn’t making contact anywhere, it isn’t the belt driven alternator, I had the prop dynamically balanced. Plan to look at the plugs and injectors next. I don’t have an engine monitor...yet. 4 new cylinders installed 30 hours ago at annual.

I’ve had a couple guys suggest removing and reinstalling the prop 180 degrees. My understanding was that these 3 blade props are “indexed” and that it wasn’t even possible to rotate it 180 degrees?

Hoping it’s not the counterweights and would like to look at all the other possibilities before we split the case.

Anyone have any positive results to report from rotating a 3 blade prop 180 degrees?

Thanks,

Kirk

How long ago did the vibration start?
Was your prop balance after those new cylinders?

My personal radar would be painting returns on the recent cylinder wrenching.

With a prop balance it’s critical to have them give you the spectrum analysis report. That’s where the good stuff is.

4 factory new cylinders 30 hours ago. Prop balance 2 days ago. Made little to no difference. I don’t have a baseline vibration as I never flew the airplane prior to the new cylinder install. It’s a tolerable vibration just annoying and since I know how smooth everything is with just the right engine running while in flight, I’m thinking the left engine should be similarly smooth, but engines and props are unique of course.

Kirk

I have a 3 Blade McCauley on my Bonanza. It can be indexed 180 degrees. Typically on the Bonanza if installed correctly it is 1 blade up, Y up and it is 180 off. Your installation should specify the correct way to install. Given that it is a twin, would expect Left and right to be installed the same and both to stop in same orientation.

My left engine is always one blade up. Right engine is one blade down. I’ve looked at a lot of pics of Crusaders and they’re all over the map.

On other Continentals (Baron 58s) you install the three blade props with one blade lined up with the TC mark on the crank flange. Check your MM.

Crusader Maintenance manual says

Note:
Install the propeller such that one blade is positioned over and aligned with T/C mark, located on flange of engine crankshaft.

If they are stopping in different positions I would say pull the spinner cones or nose bowls, I forget which side it is visible on for the T303 and see if you can ID which prop is not correct.

They should both stop in the same orientation. I would guess Y up with one blade down so it could possibly be hand propped if needed and so water can drain from the spinner better.

If both are not oriented together the synchrophase knob may not work correctly or the pulses to the cockpit will be different.

Crusader Maintenance manual says

Note:
Install the propeller such that one blade is positioned over and aligned with T/C mark, located on flange of engine crankshaft.

If they are stopping in different positions I would say pull the spinner cones or nose bowls, I forget which side it is visible on for the T303 and see if you can ID which prop is not correct.

They should both stop in the same orientation. I would guess Y up with one blade down so it could possibly be hand propped if needed and so water can drain from the spinner better.

If both are not oriented together the synchrophase knob may not work correctly or the pulses to the cockpit will be different.

Thanks Charlie, I saw that in the MM as well. After talking to the cylinder shop, I’m leaning toward it being an issue with the piston weight. 2 of the new cylinders are opposing 2 of older cylinders. The shop says this could cause in imbalance due to the different weight of the new pistons vs the old pistons that they are opposing. He suggested installing new pistons that are weighted the same as the new ones in the 2 older cylinders. I’m swapping props tomorrow to at least be able to rule out a prop issue.

Kirk

I realize this is a different airplane, but Roy Shobchuck was having vibration issues with his fix gear Cardinal(Lycoming 0-360) and when he rotated it 180 degrees the vibrations went away.

Vince

Curious to hear what you learn on this, please keep us posted.

In my many years of chasing vibrations clocking the prop 180 degrees always made a difference for me. Sometimes it was smoother sometimes worse. Bad or incorrect counterweight pins causes vibration. I never experienced vibration that I could feel on a twin because it is very high speed. It will break things but you can't feel it or hear it. On a single engine installation it sometimes causes an audible sound magnified to the cockpit by the firewall. On an O-470-U with the wrong pins installed it is a G flat hum. Many years ago the factory built a bunch of new "U"'s that were installed in new 182's. Variance in piston weights will register on vibration sensing equipment but will not cause a noticeable vibration. Incorrect compression ratio pistons will cause a noticeable vibration.
High compression pistons opposite low compression pistons will vibrate until detonation takes them out! How did you check the alternator? We had a 340 a few years ago that had rebuilt alternators installed. Shook like a wet dog. NEW alternators fixed the problem after we chased down a lot of ideas that it was counterweights. lifters, etc.

Thanks Charlie, I saw that in the MM as well. After talking to the cylinder shop, I’m leaning toward it being an issue with the piston weight. 2 of the new cylinders are opposing 2 of older cylinders. The shop says this could cause in imbalance due to the different weight of the new pistons vs the old pistons that they are opposing. He suggested installing new pistons that are weighted the same as the new ones in the 2 older cylinders. I’m swapping props tomorrow to at least be able to rule out a prop issue.

Kirk

Just a verification of ground state, do you have an engine monitor? If so, are all of your cylinders operating similarly? I had a partially clogged injector causing pretty bad vibrations on a 520.

The 303 has an alternator with a belt unlike the other 300/400 series Cessnas.