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Mooney M20F excessive vibration - April 2, 2004

I have a 1967 Mooney M20F. I am looking for someone to do a full spectrum engine balance to help smooth things out. I recently had a new #1 cylinder put on it (about 15 hours ago) and the prop has about 55-60 SMOH. Do you, or do you know of someone, that can do this for me?

Thank you,
K.B.


Roger's Reply:

     You are trying to resolve some vibration issue.  Dynamic propeller balancing is the last part of the solution in fixing a vibration problem.  From experience, Mooney's with tired engine shock mounts tend to generate a-lot of excess vibration.  If the shock mounts haven't been replaced in the last 10-12 years, the mounts needs to be replaced.  Unfortunately, this rarely gets done, because the installation of new mounts requires removing the engine mount from the firewall (time consuming).  Next, a valve inspection needs to be done on the remaining three cylinders. The tightly cowled Mooney's tend to have sticky intake valves.  The fuel injectors need to be cleaned and flow checked  for matched fuel flow.  Uneven fuel flows cause engine roughness at cruise.  Magneto breaker cam symmetry needs to be checked.  Too often the opposite sides of the magneto cam can be off by more than 3 degrees of timing.  This spread in cam symmetry leads to either advanced or retarded timing of the mag 180 degrees from where the mag is timed on a 4 cylinder.  Magneto cam dissymmetry leads to engine roughness.  The induction system needs to be checked for leakage.  Your specific engine can have induction leaks at the o-rings for the intake tubes in the sump; induction leaks cause unbalanced air-fuel ratios between cylinders.  A direct compression check would verify that the overhauled cylinders have the same compression.  A case pressure check will verify that there is no excessive leakage past the rings.  Then you can make a good running engine run smooth by dynamically balancing the propeller-engine mass.  It is very common to try to fix or cover up a mechanical, fuel, or engine timing problem by dynamic propeller balancing.  

Roger

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