Filtered Air Box Maintenance and Repair

Added 5/11/2009

Over the past 3+ years that I've been flying there haven't been too many maintenance issues with the plane at all, but recently some people started to talk about one possible one.  Thanks to David McNeill, I took the time to recheck my air box and found I had a problem.  The problems are these:
  1. For some builders, the air filter is rubbing through the bottom of the air box fiberglass.
  2. I would be that for MOST builders, the rivets that are put through the fiberglass alone won't hold up.
For the issue of the filter rubbing through the air box, all I can see as a good fix is either line the bottom of the airbox with a thin aluminum sheet riveted and epoxied in, or make the air box fit the filter snug enough so that it doesn't rub.  Mine was pretty snug. When you stuff the filter under the metal plate, it is pushed in pretty good.  I did have a very slight ring in a couple places where you could tell a tiny bit of wear occured , but not enough to warrant doing anything about it at this time.  I'm nearing 500 hours, and if it keeps on at the same rate, I'll be able to change it at TBO or something.  If I need to do something sooner, I'll bond in some aluminum.

The issue that caused me my problems was that the alternate air door that rivets to the bottom of the airbox wasn't installed with any internal doubler.  This is a definite oversight in the design, as you really can't expect those rivets to hold long-term in fiberglass.  The fix is simple though...just cut a ring of aluminum...I used .050 aluminum, and make a doubler that you can then rivet to the inside.  I added a couple of extra rivets, as well, for more security, and I used standard AN4 countersunk rivets.  It wasn't a hard job, but if you're still building, just do it right from the get-go and you'll be happy you did.


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