Air Filter & Air Box Installation

In doing the annual on my RV, our A&P has found kind of an unusual air
fitler installation. As you guys probably know, the bottom of the
accelerator pump extends about 1/2" below the surface of the carburator,
where the top of the air box is attached. The accerator pump bottom then
extends about 1/2" into the air box. Unfortunately, where it protrudes
into the air box just happens to line up exactly with where the edge of
the air filter mates up to the top of the air box. The solution that
the builder of my plane used was to simply cut out a knotch in the air
filter gasket edge about 1/2" and then re-form a new seal around the
accelerator pump w/ RTV silicone. We're looking for an improvement, to
eliminate the possibility of some RTV material becoming dislodged from
the makeshift gasket and being ingested into the carb. We've looked at
offsetting the air box so it's not centered on the carb inlet but then
we're worried about missalignment with the air inlet in the cowl!
ing.
We've also discussed using an automotive air filter that consists of a
wire basket and foam filter, thinking we could deform the wire basket
to mis the accerator pump hump and the foam would still conform to the
basket, essentially creating a filter that wasn't perfectly round. Have
any of you run into this problem and if so, what was your solution?
Thanks for the help. Rick Luck

In the plans, VAN's calls for cutting the filter and using RTV to reseal around the hump.I guess you could make a spacer and a shorter filter, but other than that it would creat a lot of work in redesigning a new air box.
I have not heard of anyone having a problem with this, and there are a LOT of RVs out there flying like this.

proseal

A common variation to the RTV red silicone is using proseal. Some folks have concerns that the RTV will break down with aviation fuel. While I built mine per the plans and substituted proseal, I keep waiting for someone to find a better way and share it with us. Better, IMHO; would be not having to cut and form the filter to the carb. On the plus side, there are tons of RVs flying with this set up. I have inspected mine a couple of times and the proseal holds real well. Jack

Rebuild the airbox

I'm with you. That "gob of RTV" deal has got to be the most unprofessional design on the entire plane. And completely un-necessary.

I simply stretched the airfilter around the accelerator pump and re-cut the baseplate to fit. It wasn't that big a deal. It amazing that Vans would suggest such a rinky-dink setup.

You still have to use RTV to seal the baseplate around the float bowl drain, and on both my annuals I've found it already starting to break down. There's enough fuel vapor in the vicinity to destroy RTV. But you can't use Proseal because you've got to be able to drain the float bowl every year. The only thing I know to do is to be very careful to apply the bead from the outside so there's nothing to break off inside. It sure makes me wonder about all those guys with that hunk of RTV right on their air filter.

question for jonbakerok

jonbakerok said:

But you can't use Proseal because you've got to be able to drain the float bowl every year.

Click to expand...

My set up may be different around the float bowl. Anywhere I used proseal, I also used a release agent (#5 grease) so that it didn't stick to my carb. After set up I cleaned everything real well to remove the grease residue. The proseal just formed around those areas and doesn't actually adhere to the carb. It just adheres to the airfilter. How would proseal or RTV prevent you from draining the float bowl once you remove the air filter box and top plate? thanks, Jack