Question Engine vibration

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17 Mar 2024 08:26 #4237 by STEVE ELLS
Replied by STEVE ELLS on topic Engine vibration
Hello Helio;

Is sounds like your mechanics know what they're doing.
 
Those cylinders definitely were due for replacement.

Thanks for getting back to me with the solution.

Happy Flying,

Steve

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15 Mar 2024 11:22 #4235 by Helio Mario Pimentel
Replied by Helio Mario Pimentel on topic Engine vibration
Hi Mr Steve and all felows,

The problem turned out to be an excessive gap in two of the exhaust valves, discovered while checking the 400-hour Lycoming Service bulletim (cyls 4 & 6).
They also found cracks around the valve seat and spark plug hole.
Both cilinders were replaced.
After that the problem went away ...

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26 Aug 2022 16:35 #3592 by Helio Mario Pimentel
Replied by Helio Mario Pimentel on topic Engine vibration
Hi Mr Steve Ells,
Thank you so much for all these guidelines. I appreciate all your monthly magazine writings.
I will pay attention to the points you mentioned. I have always noticed this vibration when doing the runway threshold checks, around that range, when incresing the RPM. At the test point the vibration disappears and in the cruise flight nothing wrong comes up.
Helio Mario - Brasil

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23 Aug 2022 08:25 #3586 by STEVE ELLS
Replied by STEVE ELLS on topic Engine vibration
Hello Helio;
I am sorry I've taken so long to reply to your question.
It's very difficult to answer this type of question.
As I'm sure you know, intermittent engine problems are extremely difficult to troubleshoot.
Since the vibration does not occur during the entire RPM range, there's probably nothing wrong with the reciprocating parts of the engine.
Which points toward an ignition problem or a fuel delivery problem.
You didn't say anything about lack of power or excessive fuel usage, so I believe you need to start the trouble shooting with your ignition system.
Have you tried running the engine on one magneto while you feel the vibration? If the vibration only exists on one magneto, that shows that the magneto is causing the problem.
You can try running the left engine on the ground at 1900 rpm for 2 or 3 minutes, then after shutting it down, feel each exhaust pipe. If one is cooler than the others, I would check (or change) that spark plug.
Have the magnetos on the left engine be inspected internally since the overhaul? Both Continental (Bendix) and Slick magneto companies suggest that magnetos be inspected internally every 500 hours. If yours are beyond the 500 hour window, I suggest you send them to a good magneto or accessory shop, or buy the tools and manuals required so your local mechanic can safely disassemble, inspect and change any worn parts.
Spark plugs aren't usually intermittent; but there's one check I suggest. The internal electrical resistance from the contact end to the firing end of a spark plug must be below 5,000 ohms. This is an easy test with an ohm meter. Replace any spark plug that has an internal resistance of greater than 5,000 ohms between the spark plug lead contact and the center conductor at the firing end.
Another quick way to determine if the magneto (s) are the cause of the problem is to switch the magnetos from the left engine with the magnetos from the right engine if the part numbers are the same. If the problem follows the magneto, that's shows that the magneto is the problem.

I hope these tips help.
Please let me know what you find.
Best,
Steve

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16 Aug 2022 16:51 #3576 by Helio Mario Pimentel
Engine vibration was created by Helio Mario Pimentel
Hi Piper friends,
I´d appreciate your tips on vibration of the left Navajo PA31-350 engine that starts at 1800/1850 rpm and ceases at 2000/2100 rpm.
Engine: total 2400 hs, 800 hs after overhaul
Thank you
Helio Mario – Brasil

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