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FAB problem

Janekom

Janekom

Well Known Member
Patron
Our 7A now has done 140 hours and during an inspection we found that the air filter has chafed right through the FAB. It is now right through for about half of the circumference.

Did anyone experience the same problem and secondly how do we prevent this from happening again.

Thanks.
 
Something similar happened on mine around 400 hours, but it was only perhaps a three inch long section that wasn't chafed through, but was on the way. I cleaned it up well, and laid in several layers of glass with epoxy. No signs of any problems at 940 hours. I laid the glass completely from side to side, so that no single piece could peel loose and go for a ride through the engine.
 
Fit?

AlexPeterson said:
Something similar happened on mine around 400 hours, but it was only perhaps a three inch long section that wasn't chafed through, but was on the way. I cleaned it up well, and laid in several layers of glass with epoxy. No signs of any problems at 940 hours. I laid the glass completely from side to side, so that no single piece could peel loose and go for a ride through the engine.
Click to expand...


Alex.... do you think the extra layers you added made the filter a tighter fit?

gil A
 
I was just thinking the same thing as Gil. The filter must be tightly compressed between the air box and the top cover. This will isure no air leakage past the filter and should prevent it from "walking".

Larry
 
My filter seemed a little loose after completing the FAB. I poured in a layer of epoxy resin in the bottom to smooth it out and add about 1/16" to tighten the filter up a bit. It worked out well.

Roberta
 
I do think it would have had to tighten up the fit. However, there is still evidence that it works against the fiberglass bottom and aluminum top. I suspect this is when the engine moves up and down, the FAB tends to pitch in kind, as the forward portion is somewhat held by the cowl. The filter has to slide somewhere. The filter has definitely worn against the aluminum top plate.

Watch that top plate - many, if not most, have seen cracks sooner or later on them. I'm on my third one - they have cracked at around 400 hours or so.
 
robertahegy said:
My filter seemed a little loose after completing the FAB. I poured in a layer of epoxy resin in the bottom to smooth it out and add about 1/16" to tighten the filter up a bit. It worked out well.

Roberta
Click to expand...

Roberta, if I understand correctly, no additional glass was added? If this is the case, you might want to keep an eye on the epoxy so that it doesn't decide to delaminate.
 
The epoxy is well established on the bottom of the FAB. It is a solid cast over the entire bottom and pinned in by the filter and the rivets that hold the bypass opening. It's held just fine for 4 years.

If the FAB and nozzle are correctly built and spaced and you have the rubber isolation seal correctly made, there should be no movement or rubbing between the two that would cause damage. I have never had any problems like that.

One thing that I did notice on mine was the nose gear leg was very close to the FAB. I heated the area and formed an indentation in the FAB to ensure proper clearance.

Roberta
 
Do you lube the filter flanges?

I have about 400 hours on my RV-6A and I have had the box apart many times working modifications and replacing the filters. I know the filters are advertised to be cleaned and not replaced and I did that once but usually I replace them - I want all of the air flow into the carburetor that I can get (O-360-A1A). My airbox still looks like new. I do lubricate the rubber surface of the filter each time - the last few times I used EZ-Turn. My filter is clamped between the plate and the box. I will keep an eye on it but I do not sense that I am going to have a problem.

Bob Axsom
 
Special grease...

Bob Axsom said:
I have about 400 hours on my RV-6A and I have had the box apart many times working modifications and replacing the filters. I know the filters are advertised to be cleaned and not replaced and I did that once but usually I replace them - I want all of the air flow into the carburetor that I can get (O-360-A1A). My airbox still looks like new. I do lubricate the rubber surface of the filter each time - the last few times I used EZ-Turn. My filter is clamped between the plate and the box. I will keep an eye on it but I do not sense that I am going to have a problem.

Bob Axsom
Click to expand...

Bob... Challenger (the K&N filters with "FAA/PMA" stamped on them and an expen$ive price tag...:)...) sells a special grease for this.

Aircraft Spruce sells it as CHALLENGER SEALING GREASE 08-04954

I use it on my Tiger, and it seems made for engine compartments and holds up under the cowl... each annual, it looks like it was just put in...

Bottom of this web page...

http://www.aircraftspruce.com/catalog/eppages/challengerairfilter.php

The hot rod shop probably has a K&N non-FAA equivalent....:)
It seems greasier and thinner (but not runny) than EZ Turn/Fuel Lube.

gil A
 
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