Vibration M20C

[Boilermonkey]

Our girl likes to shake. We've had the prop dynamically balnaced and replaced the engine mounts. At 2500 she's fine, but 2400 and 2300 RPMs she vibrates quite a bit. Any ideas?

 

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[Sean S]

I had a similar issue, mild to moderate vibration at lower than full RPM and rich of peak, it turned out to be a clogged injector. If you have  EGT on all cylinders it will tell you if you have an injector problem.

[Htwjr]

I doubt that it is an injector problem on a C model.  Maybe an intake leak.  Just guessing.

[Jim Peace]

17 hours ago, Boilermonkey said:

2400 and 2300 RPMs she vibrates quite a bit. Any ideas?

 

 

 

That’s the only reason my girlfriend flys with me 

[redars]

Vibration issues are sometimes difficult to pinpoint.  Try examining the spinner, I was surprised of how much vibration a cracked spinner may cause.

[larryb]

When I replaced the engine mounts in my J it got noticeably smoother. But you did that already. I found the best rpm to be 2500 so I always just ran there.

[carusoam]

Long shots...

Expect the unexpected...

How well balanced are the engine parts... are they all the same cylinder type, age, hours...?

Anything honed oversized?  Evidenced by oversized rings on one or more cylinders?

How are you measuring the vibrations?

I saw vibrations in my M20C appear as bubbles in the wet compass that was shaking about so much...

End result... there was a pair of broken welds on the engine mount... three bolts holding the engine in place instead of four...

These were the days, long before MS...

Memorable lessons in plane ownership.

Best regards,

-a-

[takair]

Can you give a better description of the vibration?  High frequency? Low frequency?  What do you see moving or what do you feel?  Prop balancing is typically optimized for one RPM...if you fly at another it may not be perfect.

[Guest]

A broken engine mount tube?

One oversized piston/cylinder assembly and three standard sized?

Clarence

[Boilermonkey]

Thanks for the ideas I'll discuss with the other owners and A&P.

Is describe the vibration a high frequency.

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[carusoam]

18 hours ago, M20Doc said:

A broken engine mount tube?

One oversized piston/cylinder assembly and three standard sized?

Clarence

Two ears broken off a lower leg of the engine mount...  a pickle fork with both tines separated away.

The tube was solid.  Mostly, the tube would come to rest atop the square block that was bolted through the fire wall... the ears were bolted in place and didn’t appear to be an issue... just they were no longer welded to the tube...

One day the tube slipped off the block, and the engine dropped noticeably lower to the cowl... but not in contact...

Enough to think it was time to have the mount’s rubber parts replaced... 

on a later flight, the tube moved back on top of the mounting block... appearing to have fixed itself...

Knowing M20Cs have never fixed themselves before.... It was time to get a closer look....

Four bolts usually are holding 180 horses at the front of an M20C... unless one of the mounting blocks is no longer attached to the engine mount... then it is three...

Nothing makes you feel more like a test pilot than flying around on 3/4s of an engine mounting system... or hearing 3 matching valve taps and accepting the fourth one to sound differently than the others.... (on start-up)...

This was a decade ago, so my memories of the whole thing are a bit fuzzy... There was no MS to ask... ‘has anyone seen this before’...

The plane went to the MSC for that discovery... ended in the hands of a mechanic as a project....

Best regards,

-a-

[kerry]

I noticed in your picture your plane has a 3 blade prop.  When I was shopping for a prop I was interested in a McCauley Black Mac.  The shop I was dealing with highly recommend I stay away from the 3 blade Black Mac because of vibration problems they could never solve on Mooneys.  You could also look into indexing your prop.  I have an experimental with a Lycoming O-320.  It had some bad vibrations around 1200-1500 RPM's.  After I indexed the prop my vibration problem went away.