I have developed a vibration recently when I set the propellar to cruise speed on my comanche 250. I normally use 21 manifold and 2350 at altitude. Any suggestions.

Todd Skalsky

Try an extra 50 to 100RPM. 0-540's seem to like 2400-2450RPM for smooth running. Then you might take an RPM checker up with you next time your out and see just how accurate your tac is. Could be the tac's started reading high or low so your not in that old RPM sweet spot. Ray B

I have also developed a vibration on the 250 using a McCauley three blade prop with 292 hours on it, had it balanced but did not help. Thinking of changing the mounts next, any thoughts out there.

Leo, yep, change the mounts. They are only good for about 3 yrs or 500 hrs, whichever comes first. When they get hard, they don't isolate very well anymore. Get with Mac, and make sure you are installing the correct isolators for your prop/engine combination. Also, any time a blade is dressed it changes things significantly. The three blade macs are very suseptable to leading edge disturbance that causes vibration. Use a medium driwall sponge to smooth the prop to the touch, as well as the paint transition.

Todd, same for you. However, I would also make sure that Lyc service letter 388 (valve wobble test) was acomplished as a sticking valve can also be a source of vibraton, especially if it came on suddenly with nothing having been done to the prop.

My mechanic is recommending the same thing - change the mounts. He pointed out to me that over time the lord mounts degrade and in mine you can actually see a very small space on the back of the lord mount to the harness it attaches to. Expensive, but needs to be done.

Scott

Thanks for the answers.
Be aware the STC from Mac requires 4 new lord mounts J3804-41 I had this ones installed now I get a clunk when I start the engine, the STC got change to a new mount J3804-42 but they have not made any changes to their website requiring the old ones. Now I have to replace the mounts again.

I also had a EDM 830 installed on the comanche 250, well worth the money spent.

McCauley wer nice to not only provide me with new engine mounts but also covered the cost of the installation. Great customer service.

Thanks service department and Rebecca Williams.

Any update on the vib's? I have a 250 as well and has the viberation at the same power settings. I had the propeller dynamically balanced and replaced the gov.