Engine vibration after 3blade propeller.

[Jeff Odell]

I recently installed a new 3 blade propeller in my Comanche 250 with a o-540 engine. After the first flight I noticed a vibration when I decrease the rpm to 2400 or below. So I had the prop dynamically balanced. We got the prop to .07ips This did not change anything. The engine or airframe still vibrated. I contacted McCauley and they had some engine mounts that they thought would fix the issue. It did not. The balance A/P checked out the airframe and we corrected all movable surfaces that were loose or worn. This did not help. I have checked and rechecked if something from the engine was touching the cowling but I don't see any evidence of this other than the rubber baffling and felt seals in front of the engine baffle.

I put on the old propeller in frustration as I remember my plane used to be super smooth now to find out now the old 2 blade propeller also now has the same issue. My thinking now is the engine is running rough or incorrectly? Have you ever heard or run into this? I do notice that if retard the throttle back to 10-12 MP the vibration smooths out (still 2400rpm). When I apply the power again the vibration returns. The vibration is not severe but not smooth like it used to be.

Any help where to go would be appreciated.

Jeff

[James Turner]

Hi Jeff,

Sounds like you've had a tough time of it. I am certainly no expert in this area and I own a -180 with the old two blade prop but one thing that fixed the symptoms you describe in my aircraft was changing from massive electrode plugs to Tempest fine wire plugs.

I was told that engine 'roughness' (actually felt like vibration to me) in association with high power settings could be caused by weak and therefore uneven ignition. I guess it is the same principal as leaning the mixture too far and experiencing engine rough running? Anyway, changing my plugs to new Tempest fine wire plugs made a big difference to the engine smoothness at high power. I guess checking your mag timing and ignition leads may also be a good idea...

Good luck...

James.

[WMD]

[N3322G]

Jeff,

The report from the prop dynamic balance may give you some direction. It has been a decade but IIRC there are 9 parameters on that report - at least there were for the Twin. The shop couldn't tell me what the meanings of the results past the first one were so I called the manufacturer of the device - today it is probably on the internet. After much research, it was the engine mounts that had been improperly torqued by the shop that handled the remove/install of the engines. Now I have the torque checked every annual and at the most recent annual had the mounts changed after 4 years. Both husband and I noticed there was less vibration after the mounts were changed - so something else you might check.

I credit Zach Grant with the advice to change mounts every four years when he ran the CPPP course that is now CPTP - worth every penny. http://www.comanchetraining.com/

[bernard nowlen]

I think none of the 4 cylinder Lycomings have counter weights. You would have to call Lycoming with your data plate info of check the engine parts book to get it. A guy at the airport put an STC'D 3 bladed prop on a Mooney with an O-360 and ended up going back to the 2 blades due to excessive vibration when compared to his 2 bladed prop. As said in this thread it could be the motor mounts. I had a 63 310 that had 3 bladed props(per stc) and you could feel the vibration through the floor boards. It had the wrong motor mounts installed when the previous owner upgraded to a colemil conversion (IO-520) and the 3 bladed props were installed. In 64 Cessna changed the motor mounts(bigger footprint) when the 3 blade prop was a factory option to eliminate this problem. Bernie

[bernard nowlen]

I stand corrected. After doing some homework it appears the 200HP IO-360 has counterweights and the O-360 (180 HP) doesn't. Just a thought. bernie