Filtered Air Box Size

Our flying RV-6 originally had an O-320 and now has a new Superior IO-360 in it. During the conversion to FI, the carb heat door became the alternate air source. Unfortunately the door came loose a few months ago due to cracking of the top plate of the air box at the ends of the door hinge on both sides. After removing the door completely, we are still flying (effectively with both normal air and alternate air sources open at the same time) but during our upcoming annual we want to make a repair.

We had Vans ship us a new FAB-360 kit so we have all the parts we need just in case we need to rebuild the whole thing. However our plan A is just to make a new front half of the top plate (VA-130-B) to rivet onto the existing top plate, with a new D-shaped cutout. However I am worried that the new air box top plate is narrower than the old one (which probably dates from about the year 2000). I'm at home and don't want to go to the airfield and de-cowl to check, so I'm wondering if anyone knows if the dimensions of this part have been changed over the years, or what the old dimensions were?

Has anyone else experienced the same failure? Did you come up with anything clever to prevent a recurrence?

Thanks for any help or suggestions.

If the airbox you have now is slightly rounded on the bottom, and the filter is installed with an oval aluminum plate clamping onto the bottom of the filter, I think the new to plate will be slightly wider.

On my RV-6, the FAB carb heat hinge is a wear item. After replacing the aluminum hinge once, the 2nd time I replaced the aluminum hinge with a steel hinge. Steel hinge still wears but it lasts a lot longer. The steel hinge also has been replaced once. Yes I am on my 4th hinge after 3,300+ hours.

Mine also failed

AndyWW said:

Unfortunately the door came loose a few months ago due to cracking of the top plate of the air box at the ends of the door hinge on both sides.

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Mine cracked on both ends and then the whole assembly sort of flopped down into the intake area. At the suggestion of someone here, I discovered that it was rubbing/bucking against the cowling, likely during startup. I filed away a bit of the cowling where it was making the most contact. I also sort of "doubled" the bracket that holds the hinge to the top of the box (looking into the intake the bracket now looks like an H instead of like a U, if that makes sense).

With any luck, my fix will be more durable than the original. But in general, I think this is a high wear area that rewards frequent inspection.

Thanks for the responses - sounds like this is a bit of a problem area. I will investigate the possibility of a steel hinge.

On the size question, we don't have the plate underneath the filter, just fiberglass (which does sem to be wearing a bit, and we also have the shrinking filter problem which I think mean there is air leaking under and over the filter). But I am pretty sure the old top plate is actually larger than the new one.

It may be that the best solution is to cut a flat piece of 0.040" sheet, make the D-shaped hole in it, attach the door hinge, and then wait for the annual to cut, bend and rivet the new piece to the old top plate.

Doug - do you have a picture of your H-bracket?

AndyWW said:

Doug - do you have a picture of your H-bracket?

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I'll try to remember to get one the next time I'm out at the hangar. Basically I replicated the original u-shaped bracket, flipped it upside down, and sandwiched the hinge between the two brackets. Not sure how much strength it added, but maybe a little.