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  #1  
Old 05-25-2017, 04:14 PM
Piper22/20 Piper22/20 is offline
 
Join Date: Jan 2015
Location: Weirsdake, Fl
Posts: 7
Default Low rpm vibration

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

Last edited by Piper22/20 : 05-25-2017 at 04:17 PM.
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  #2  
Old 05-26-2017, 12:35 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,248
Default 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.
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built a few RVs, rebuilt a few more, hot rodded more, & maintained/updated a big bunch more
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  #3  
Old 05-26-2017, 01:04 AM
Piper22/20 Piper22/20 is offline
 
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Location: Weirsdake, Fl
Posts: 7
Default

Thanks vibrates with or without spinner.
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  #4  
Old 05-26-2017, 04:04 AM
Bob Martin's Avatar
Bob Martin Bob Martin is offline
 
Join Date: Jan 2005
Location: Charlottesville, Virginia
Posts: 1,240
Default 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.
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Bob Martin
RV-6, 0-360 Hartzell C/S, Tip up, 1200+TT
James extended cowl/plenum, induction, -8VS and Rudder. TSFlightline hoses. Oregon Aero leather seats.
D100-KMD150-660-TT ADI2- AS air/oil seperator. Vetterman exhaust with turndown tips.
Louisa, Virginia KLKU N94TB
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  #5  
Old 05-26-2017, 05:13 AM
Piper22/20 Piper22/20 is offline
 
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Location: Weirsdake, Fl
Posts: 7
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Do you remember where the intake leak was and how you found it?
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  #6  
Old 05-26-2017, 05:41 AM
Bob Martin's Avatar
Bob Martin Bob Martin is offline
 
Join Date: Jan 2005
Location: Charlottesville, Virginia
Posts: 1,240
Default 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.
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Bob Martin
RV-6, 0-360 Hartzell C/S, Tip up, 1200+TT
James extended cowl/plenum, induction, -8VS and Rudder. TSFlightline hoses. Oregon Aero leather seats.
D100-KMD150-660-TT ADI2- AS air/oil seperator. Vetterman exhaust with turndown tips.
Louisa, Virginia KLKU N94TB
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  #7  
Old 05-27-2017, 09:05 AM
Radioflyer Radioflyer is offline
 
Join Date: Nov 2009
Location: Boston
Posts: 162
Default 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.
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  #8  
Old 05-28-2017, 07:24 AM
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airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,357
Default

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!
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2021 dues paid
N16GN flying 750 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, IFD440
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #9  
Old 05-28-2017, 07:50 AM
Flyingleap Flyingleap is offline
 
Join Date: Nov 2012
Location: Cincinnati,Ohio KHAO
Posts: 133
Default 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
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RV-7 want-a-b
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  #10  
Old 05-30-2017, 06:22 AM
Piper22/20 Piper22/20 is offline
 
Join Date: Jan 2015
Location: Weirsdake, Fl
Posts: 7
Default

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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