Odd vibration now at full power (582 GSC)

[LSaupe 123]

Ran into a problem tonight.  After my third take off I started to notice a vibration at full power.  It disappears when I pull the power back to 6000 RPM.

I was hoping maybe one of the blades had rotated, but unfortunately they are all spot on the money.  Same with tracking.  

Grabbed the engine and did a visual on the engine mounts (Lord mounts) and they appear fine (to the naked eye anyway).  No excessive movement when trying to move the engine.

Have been running on the rich side as of late, any chance something simple as a plug breaking down a bit at full power?  

Hopefully not a gearbox issue.

Feels like a lower frequency (like prop speed or less).  Whats odd is that this bird has never had any vibration (even at full power).  Now it is here.  No damage to the prop that I can find.  Anyone experience something similar with a GSC?  Today was also the coldest day I have flown (~ 30F outside).

Other thoughts?

 

 

[C5Engineer 1170]

There was recently a discussion on this very topic. Can't remember what the outcome was but here's the thread. 

 

http://www.avidfoxflyers.com/index.php?/topic/3480-engine-vibs-gsc-prop/#comment-26631

 

 

[LSaupe 123]

Thanks for the heads-up.   Most look like a known previous condition (though hard to say when issues may have started for them).  Mine changed after a landing.  Real odd, something changed.

[akflyer 1427]

if you have been running rich, I would pull the plugs and check them.  Check your plug wires as well.

 

[BryceKat 125]

How do you know you've been running rich? Using a fatter jet?

[LSaupe 123]

Running a high needle position, due to an errant high EGT indication (turned out to be a bad EGT instrument, verified by a air/fuel ratio sensor I installed and the new EGT instrument).  Running around 1050 now at full power and 1125 at part throttle (and that is when its cold outside).  Plugs look very rich as well.  Will swap out with new ones and see what happens. 

[LSaupe 123]

Just some follow-up in this problem in case anyone is interested.  The good news is that the vibration is now gone.

Upon further inspection I noticed that the left, aft, upper side engine mount bolt had been making intermittent contact with the upper Lord mount topper washer (the fender type washer on top of the mount).  I relieved the washer and also installed a new set of plugs.  Took it up this AM and all is well again.

Not sure which item fixed the problem (I suspect the bolt head/washer issue, maybe a combo of both), but... we are back in business now.

[Av8r3400 1179]

Glad to hear the issue is fixed.  Vibrations can be frustrating to find and fix...

[Knuckledragger 135]

Thanks for the detailed update.  Adding to the collective wisdom often gets forgotten after a problem is solved - now we all benefit from your experience