Air Filter Fit Inside Airbox

flickroll · #1 05-03-2009, 05:49 AM

Can anyone direct me to the drawing and/or instructions for fitting the K&N filter inside the airbox of an updraft carbureted O-360-A1A? I bought a previously flying RV-8 and it seems to me the air filter is not sealing properly between the plate that is attached to the carb in particular, and probably not sealing well against the fiberglass airbox either. The top plate of the airbox has angles riveted around the perimeter to position the filter, but theses angles are installed too far outward such that some of the rubber seal of the K&N 'hides' inside the top plate of the airbox. The rubber seal of the K&N will not contact the plate that is attached to the carb because part of the seal on the filter slides underneath the top plate of the airbox. Seems what I need to do is to install new angles to the top plate of the airbox to insure the entire K&N rubber seal is 'visible' to the plate attached to the carb. Also, how do I ensure a snug seal between the lower K&N rubber seal and the fiberglass portion of the airbox? Some sort of weather stripping? I am hesitant to do this in case it ever came loose and gets sucked into the engine. Hope this was not too confusing..... Thanks

PaigeHoffart · #2 05-03-2009, 06:07 AM

You are correct when it comes to repositioning the angles. The filter should seal against the plate that is mounted to the carb. As far as the bottom, it just seals against the fiberglass. When you build the airbox, you position the aluminum top plate so that the filter is slightly compressed against the bottom of the airbox.

If you need to increase the filter compression after the fact, I would think a spacer plate on the inside bottom of the airbox would do the trick. I would probably attach it with some epoxy and some keeper rivets; I'd install the rivets outside the filtered area just in case one came loose.

Another option might be to drill out all of the rivets on the top of the airbox, reposition the top plate, and re-rivet with a pattern spaced between the original rivets. I'd use plan B if the top plate and bottom surface of the airbox aren't parallel.

Paige

flickroll · #3 05-03-2009, 06:11 AM

Thanks Paige for your response. Since it's a rainy day and no flying is in store for me, looks like a great day for airbox work.....

AlexPeterson · #4 05-03-2009, 10:42 AM

Jim, it could very well be that the filter has shrunk. I ran the first one on mine for perhaps 5 years, and it had really shrunk, maybe 3/4" in the long axis. Get another one to try before doing any mods - unless you've already done them!

flickroll · #5 05-03-2009, 05:38 PM

Quote:

Originally Posted by AlexPeterson

...it could very well be that the filter has shrunk. I ran the first one on mine for perhaps 5 years, and it had really shrunk, maybe 3/4" in the long axis...

Alex - I think the airbox never was constructed properly. The angles used to position the filter are in the wrong place. But....didn't get to the airbox today. Fitted wheel pants, set toe in/toe out to neutral, and pulled a bad fuel sender. Pretty busy day...

asav8tor · #6 05-04-2009, 05:39 AM

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| WARNING |
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DO NOT modify the air box by adding weather stripping, rubber, spacers that could come loose etc.

One RV was a total loss due to this (I was there for it); Another did an off field landing for the same thing.... That's 2 that I know of.

The airbox filter fit can loosen up from the normal vibration and flexing of the top plate and fiberglass box, especially if the fit was not real tight to start with. The gold-standard fix is to rebuild the box with a new top plate and lower it down to provide a tight fit.

Your engine needs a continuous flow of fuel, air, and spark. Modifications of anything to do with these three delivery systems needs very careful consideration about unintended consequences.

flickroll · #7 05-04-2009, 06:06 AM

Quote:

Originally Posted by asav8tor

DO NOT modify the air box by adding weather stripping, rubber, spacers that could come loose etc.

What I have decided to do is rivet the new angles in to ensure proper filter contact with the top plate, and then put in an aluminum lower plate in to ensure a snug fit. The bad news is the airplane, before I bought it, ran for about 300 hours with a suspect air filtering system.

PCHunt · #8 05-04-2009, 11:01 AM

The filter inside the FAB on my (purchased) RV-6A, built 1993-1997, has a top aluminum plate that is attached to the carb, AND a BOTTOM aluminum plate, with 5 or 6 long bolts holding the two plates together. In other words, the filter is "squeezed" in between the two plates. Then the fiberglass FAB goes over the whole enchilada.

The K&N filter never touches the fiberglass at all. Photos upon request.

flickroll · #9 05-04-2009, 02:30 PM

Quote:

Originally Posted by PCHunt

The filter inside the FAB on my (purchased) RV-6A, built 1993-1997, has a top aluminum plate that is attached to the carb, AND a BOTTOM aluminum plate, with 5 or 6 long bolts holding the two plates together. In other words, the filter is "squeezed" in between the two plates. Then the fiberglass FAB goes over the whole enchilada.

The K&N filter never touches the fiberglass at all. Photos upon request.

Based on that description, mine definitely needs work....

The method on your airplane sounds pretty slick...
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