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Low rpm vibration

Piper22/20

I'm New Here
Rv6 o320 sensenich metal prop vibrates between 800 and 1400 rpm. What I've done and discoverd. New mag. New wiring harness. New engine mounts. New carburetor. Replaced intake gaskets and hoses. New plugs. Timed engine. Compression check. Clock propeller. Balance propeller. Nothing worked. I noted that the warmer the weather got the less vibration occurred. This led me to believe I have a mixture adjustment problem. The more I enrich the idle mixture the less vibration I have. The airplane has a vetterman exhaust. Your thoughts please and ideas. Steve
 
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Spinner?

Had one plane that came in for prop balancing with a similar scenario. Good balancing results at higher RPMs but would shimmy just above idle. Drove us crazy going thru possible causes until we decided to try rebalancing with spinner removed, perfect results. So the spinner cone (a spun aluminum unit that had been chromed) was the culprit, a new Vans fiberglass spinner was installed and the final rebalance produced a smooth prop all thru the whole RPM band.
 
Long ez

I worked on a Long-ez that had a bad vibration at idle.
The steel engine mount was broke and we finally found an intake leaking. Not sure which came first but fixing the intake leaked cured the vibration.
I understand you have installed new intake gaskets but just adding FYI.
 
yes

It was at the head gasket. Saw blue stains.
That location is prone to leaks as the gasket fit with the small flare/flange seems fragile. Thinking ours was on the #3 but memory is fading.

Again, this only seemed noticeable at idle. But I would bet it was showing up as a lean cylinder during flight as well.

Do you know the trick about using a shop vac as a blower? Place a screen of some kind over the output and place on inlet of carb. Spray soapy water over joints looking for bubbles. You have to rotate prop as you check each cylinder to close the intake valve, and plug up exhaust. Might not be perfect as blowing is not the same as sucking but something to try.
 
intake gasket leak

A while ago, I had the same rough idle vibration on my O320-E2D (LongEz). Found an intake leak on my #4 cyl. Replaced the gasket, checked again for leak, and leak still there. Had to sand the clamp/flange on a flat glass surface to insure that it would seal evenly around the gasket. So, sometimes, it is not enough to simply replace the gasket. You have to insure that the clamp is flat and that it actually presses the gasket evenly to the cylinder, instead of just letting the gasket sit in the recess of the clamp. My rough idle was thereby resolved.

I used a DIY glycerine/soap solution to locate the leak with a pressurized induction system. I made an adapter to connect the output of my compressor at the lowest possible pressure (6-10 PSI) to the carb inlet. The Shopvac method might be better for lower pressure. Now that someone mentioned it, rotating the prop to get the intake valve closed for each cylinder leak check seems like a very good idea.
 
I discovered a broken left main gear fairing rivet that was allowing the fairing to twist and vibrate - it was resonating with the prop pulses at 2300 rpm. I was doing some cruise power testing for max range and noted a definite increase in vibration between about 2400 and 2200 rpm despite having recently gotten the prop balanced. It took a while but I found and fixed the fairing, and the vibration disappeared.

Now I have a busted-up nosewheel fairing, due to poor choice of a dirt runway that I get to fix. It's always something! :D
 
Short lived gaskets

Was talking with a engine builder last year (does about 8 to 10 Lycomings a month). He said intake gaskets have the asbestos removed which shortens their life. The problem was actually found by banner towing pilots who change the gaskets every 100 hours.

It would be the first place I would check for engine roughness
at idle. John
 
Thanks for all the responses. I need to add the this vibration also is there at the same rpm, most notable at 900 even in a power off glide coming in for landing.
 
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