The International Cessna 170 Association

My carb heat box will occassionally require a little tweaking about every 6 months or so. I'll pull the knob out and it will be stuck in the off position. I'll twiddle with it and it will then behave properly. Of course, it always works perfectly during my preflight!
Took another look at it today and I think the problem is the holes in the side walls of the box are wearing and the axel will drop down in this notch and hang up.
My question is will the rebuild kits offered by Spruce or Wag Aero do the job or just replace the box entirely. Also are these kits and boxes FAA approved? They seem awfully cheap for an aircraft part, $177 for the box. If not approved, is there another source for approved versions other then Mother Cessna?
Thanks for the advise.

The repair kits are a good, inexpensive way to get more mileage out of an otherwise sound airbox. The kits are not FAA PMA'd (approved) but so what? You are merely participating in "owner produced" parts by making a "final acceptance inspection" and rebuilding your airbox, which is then a proper repair.

Thanks - that's what I was hoping to hear.

So, does this apply to the new air box assembly? Since it's not a PMA approved part, doesn't it need a field approval? Russ Farris

I found I had the same problem during the annual, I went for the avglas kit. McFarlane owns the STC, the number is se00164se. The kit is nice but will require some brazing and riveting and a 337 when your done. All said and done it took less than a day (my buddy insisted on repainting the whole airbox). If you would like I have the stc, instructions and 337 for you to see to determine if this is the route you want to go.

Vic

russfarris wrote:So, does this apply to the new air box assembly? Since it's not a PMA approved part, doesn't it need a field approval? Russ Farris

According to the rule, FAR 21.303, the owner must "participate in the design, manufacture, or quality of the part." According to both my FSDO inspector and a local aeronautical engineer (TIC170A member), "final acceptance/conformity inspection" is a manufacturing procedure.

One comment about older leaky airboxes. I've found quite a few where the owners or mechanic has used silicone sealer on holes, gaps, or around the gasket. Gas eats silicone. Resoftened silicone then can be inducted into your engine. Bad deal

The Spruce catalog sez "Cessna 170 style heat box" and then it sez "heat box Cessna 170". Even if these are not FAA/PMA'd, and it's pretty vague whether they are or not, if you perform a "final acceptance/comformity inspection" the installation will be an approved one,by George (get it? )
At least that's what I get from George's post. Or does the "inspection" participation by the owner only apply to repair of an old beat-up part?

Eric

At $177 for a brand new airbox from Spruce, if it passes muster ("final acceptance/conformity inspection" by owner) I might be tempted to paint it,install it,and log it as "repaired airbox as required".

Eric

The earlier message I posted refers to FAR 21.303, "owner procuced parts". It doesn't say anything about owner "repaired" parts.
In any case, an A&P must install the parts or supervise their installation and sign it off.

Ok, I'm looking at fixing my old airbox, and the flap is welded to the center rod. Does anybody have any nondestructive suggestions for getting the flap out of the box. It looks like I will have to cut the ends off the shaft?

For repair on any and all air boxes contact:

Joe Rogg
1-800-244-0866, ext.165

I believe that's his main business.

Eric!

Where have you been? Glad to see that you are still around. Have you got your new Washington State Airport directory yet? I took the picture of your airport along with 59 others in the book. Work sucks sometimes...

Joe

Whoops, maybe he's not still around. That was a pretty old message.

Joe

Jr.cubbuilder
The last one I did was the avglas repair. The flapper valve was brazed onto the shaft. Being as thin as it was I pretty well destroyed it getting it off the shaft by trying to heat it enough to loosen the brazing. I think it would be a good idea to plan on replacing the flapper as well. Once it was off I drilled off the bearings and pulled the shaft and the arm side bearing came with it.