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New Engine Noise?

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Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Sun Apr 12, 2009 11:28 am Post subject: New Engine Noise?

I am in denial but I think I am in trouble.  I just turned over 345 trouble free hours on my 912ULS when I had a new noise last week.  Kind of a slight rattling noise that comes and goes.  Could not  find anything loose and the engine ran fine at all speeds.  Today I ran it without the cowl off and hear a definite but slight rattling,knocking sound at 2150 rpm on warm up.   It goes away at  2000 and 2200 and on up.  I am still flying but since I don't like off airport landings,  I have to ask if anyone has any ideas. 

 ....Please say its OK...

Oil usage is nill and has been changed on schedule since new.  Average fuel consumption is 3.7 and always non-ethanol 91 octane.

The cost and loss of flying time is going to be grim.  I don't even know where to get it fixed if I have to.



thanks in advance

Rich L

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l_luv2_fly(at)yahoo.com
Guest

Posted: Sun Apr 12, 2009 12:54 pm Post subject: New Engine Noise?

Hi Rich,



Do you have any accessories on the engine ?  I had a similar experience with a vacuum pump making an odd noise.



Also, not wanting to state the obvious there are a lot of things attached to the engine that can just plain rattle.  Exhaust systems are great candidates.



Regards,  Paul

Europa 914

         [quote][b]

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Apr 13, 2009 4:02 am Post subject: Re: New Engine Noise?

Rich,



Since the sound is present only in a very narrow rpm range, there is a good chance that it is due to something loose on the engine, as Paul stated. Remove the cowling and (without the engine running), start at one corner of the engine compartment and check EVERYTHING for the least bit of looseness.



If you don't find anything that might be causing this rattle, it could be the gearbox. At that rpm, the prop is not loaded much so it could be simply the slight rocking back and forth between the two gears which have a slight amount of "backlash". 



You can feel and hear the backlash I'm talking about by rocking the prop back and forth (in turning direction and reverse) just a tiny bit. You should note a very small movement at the tip of the blade, perhaps 1/4" or 1 cm at the most. This is normal. Do not turn the prop backwards, just check the tiny bit of backlash in the gears by rocking the prop back and forth.

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_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Rich L

Joined: 23 Feb 2008
Posts: 63
Location: North Idaho

Posted: Mon Apr 20, 2009 5:15 pm Post subject: Re: New Engine Noise?

First I want to thank you all for the ideas to make me think in another direction and I'm not gonna say that box thing. 

I found the tab on the lower cowling which slides over the radiator in a KF-7 had somehow become weak and was not fitting as firm as it did in the beginning. I had put rubber tape under it but the fit had loosened to the point where it rattled against the radiator. I am going to add a piece of fiberglass to the tab and put a thicker against of rubber in between. It was scary but the Rotax is still running great.



thanks again for all of your input



Rich

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