airbox chafing

At my last oil change, I noticed that the airbox on my 0-320 carburated engine had minor chafing at the lower left where it is rubbing against the cowling. It will probably worsen as the engine sags. My plane is painted, so I don't want to modify the cowl. If I slightly modify the airbox, what material is used? I vaguely remember that it's not fibergalss, so I think that a different resin and material is needed if I modify it. Is a slight airbox mod acceptable and what problems, if any could it cause? thanks

Build9A said:

At my last oil change, I noticed that the airbox on my 0-320 carburated engine had minor chafing at the lower left where it is rubbing against the cowling. It will probably worsen as the engine sags. My plane is painted, so I don't want to modify the cowl. If I slightly modify the airbox, what material is used? I vaguely remember that it's not fibergalss, so I think that a different resin and material is needed if I modify it. Is a slight airbox mod acceptable and what problems, if any could it cause? thanks

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I too had a (very) small amount of rubbing on my airbox - even though the clearance is pretty good when the plane is not running. I suspect there is a slight shake at start/stop. The airbox is fiberglass, so I just cut an oval out on the side, put some masking tape on the inside to serve as a crude mold, then layed up a few layers of bid fiberglass/epoxy on the outside. The net result was about a 1/4" recess on the lower left side of the airbox.

Since I had the airbox off anyway, I went ahead with Van's latest airbox bypass service notice (the one with the bowden cable rather than the magnet).

One thing you might try if the area is not too big. I used my hair dryer to heat up an area on my airbox that was too close to the nosegear leg. I heated it enough to soften the fiberglass, then I applied pressure with a pipe to reshape the affected area. You might be able to reform the edge of your airbox to add enough clearance. This way you could avoid a lot of reglassing.

Roberta