rebuilding the airbox
 

After chasing a lean misfire for two months I pulled the entire CIS setup to find a crack in my airbox. After reinstalling the engine last January I had a huge backfire the first time I started it, and the car hasn't run right since. Here's the offending crack along the right seam:

http://forums.pelicanparts.com/uploa...1114044165.jpg

So I put a sharp knife in the seam and tapped it all the way around to separate the box into two halves. It didn't look like it originally, but probably half the seam was blown out.

http://forums.pelicanparts.com/uploa...1114044343.jpg

Oops, looks like we had a pretty big fire in here!

http://forums.pelicanparts.com/uploa...1114044534.jpg

There's an interlocking channel that goes around the box. I cleaned it out with a dremel and then wire brushed all the surfaces that will get glued:

http://forums.pelicanparts.com/uploa...1114044692.jpg

Since the box is nylon, I think, and most epoxies don't stick well to nylon, I had to look around a bit to find something suitable. Devcon makes a plastic epoxy for nylon called "plastic welder II". Not cheap at $33 for four of these tubes, but still better than $450. You can tell by the industrial label that this is not your average home depot epoxy.

http://forums.pelicanparts.com/uploa...1114044837.jpg

The epoxy was thick, yellow, and smelled worse than any glue I had ever used. I had to mix it out in the driveway it was so overpowering. I laid a heavy bead all the way around and sealed her back up. A little dental mirror and a flashlight verified that the goo had squeazed out of the seam all the way around the inside of the box:

http://forums.pelicanparts.com/uploa...1114044976.jpg

It goes back in this weekend. I'll post whether or not it worked.

Great work! I made a small repair to my airbox 18 months ago and it hasn't leaked since and no more backfires! Hope yours goes as well...

I use for one 911 3M marine silicon 5200 and works great.

Nitrometano! hay thats what I was gonna say!.....try the stuff,, Talk about hold pwr. and still will let things flex if needed!!!!!!

I repair the air box 2 years ago and no problemas. 3M 5200 Silicon works great!!!

I also repaired my airbox about 2.5 years ago using an automotive silicone rubber. I found the original screws had taken a bit of plastic with them and would no longer tighten, but the closest english size (6-32 or 8-32 I think) was just slightly bigger and fit well.

I have an old airbox, from a 77. The bottom section that is cracked in yours is perfectly good on mine.

If you want to buy that instead of the glue (or the glue fails), contact me.

I'll keep that in mind. I'm putting it back in this weekend, we'll see how it works.

It appears that the airbox is made up of some kind of composite. I'm now leaning more towards polyester than nylon. I put a bit of the epoxy on an open spot on the bottom of the box as a test. When I yanked the epoxy off the next day, it took a layer of plastic with it. The "bare" spot looks fuzzy like fiberglass. I'm guessing it will hold.

OK, been almost 2 years and still holding!

Good work, BUT....you can buy good used airboxes for $125, I did with a WTB ad here. Granted that is more expensive than the $33 of glue, so that's worth a try but the good used boa is more of a sure bet. Also, I don't see a popoff valve in there. Unless I missed it, you are going to install one aren't you? $50 and I never worry about my airbox anymore.

Last, if you HAVE to glue an airbox, what about that "miracle of miracles" J-B Weld?

2 years ago I could not locate a used one. Bad timing I guess.

Pic 3 is the bottom of the pop off valve. It got blown right out of the box. There's nothing like an out-of-phase ignition to blow the hell out of a box.

J-B weld might work, but I picked this epoxy because it is specific to plastic.