Re: [COUPERS-TECH] Engine noise

[Dr. R. B.]

----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----

May I suggest the following diagnostic procedure?

 

Characterize the noise: [note: perform the first through third tests simultaneously while taxiing].

 

Write down what the noise sounds like.  Clatter? Sliding friction? Slapping? Banging?

Thumping? 

 

Determine the temperature gradient: At what CHT does the noise occur?  Only dead cold? Only warm?  Regardless of temp?

 

Determine the RPM boundaries: What are the RPMs at which the noise occurs?

 

Determine the noise periodicity:  What is the noise's 'beat?'  Does it vary with RPMs?  Constant through an RPM range? 

 

Determine the noise volume:  How loud?  Does the loudness and pitch vary with RPM?

 

Isolate the location.

 

Insure the noise is really coming from the engine bay and not under the panel or in the center section.  

 

Remove the cowl and perform the above checks as before, only noting the difference if any with the cowl removed.

 

Standing outside the aircraft idling with the prop removed [to avoid what I call the Hamburger Effect], isolate the location by means of a stethoscope or, if none is on hand, a piece of fuel line held to one ear and moved around the engine compartment until you hear the noise. 

 

If intermittent and no noise or grinding in between occurrences, chances are good that something is getting intermittent lube oil starvation.  Another good prospect:  something loose being vibrated into banging at a specific RPM.  Suggest having a pull on your bracing and anything else within reach to insure tightness.

 

Dr. R. Beeman 

----- Original Message -----

From: Steve

To: tech@ercoupers.com

Sent: Saturday, April 30, 2005 6:04 PM

Subject: [COUPERS-TECH] Engine noise

----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----

Today after 3 years on the ramp I attempted to get my aircoupe in the air.  While taxiing I pulled the throttle back to approximately 550 to 600 rpm where the engine ran rough and I briefly heard a metallic clanging sound.  After several attempts to repeat this noise I returned to the hanger to pick up my mechanic and while taxiing was briefly able to repeat this noise.  My mechanic was unable to determine the cause of the sound but did agree that it was intermittent.  We returned to the hanger and checked the compression it was 74, 72, 74, 76.  Does anyone have any idea what could be causing this noise?  What does is sound like when the valves are sticking?  The noise only occurs at very low idle with the engine running rough and then it is only intermittent.  Any help would be greatly appreciated.

 

Thanks

 

Steve T.

5634F

==============================================================================
To leave this forum go to: http://ercoupers.com/lists.htm
Search the archives on http://escribe.com/aviation/coupers-tech/

==============================================================================
To leave this forum go to: http://ercoupers.com/lists.htm
Search the archives on http://escribe.com/aviation/coupers-tech/