How To Straighten a Warped Airbox

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When replacing the air filter , I noticed the plastic
airbox was warped. Judging from the type of plastic (Kydex?) this was no
surprise. I read about using silicon sealant to build up the low areas,
but since I am familiar with (some) plastics, I decided to straighten it.
It\’s easy.
You will need:
* An ELECTRIC hot air gun (like the
ones used for shrink-wrap tubing). NOT a hairdryer, NOT a propane
* A kitchen hot mitt (preferred) or a heavy towel.
* About 30
min. including removal and reinstallation.
* You can straighten this by
eye, you do NOT need a straight edge (that will only complicate
1 – Remove the airbox. Open it up and take out the filter.
Set the air filter and the metal half of the airbox aside.
2 – This
plastic is very soft. It takes relatively little heat (as far as plastics
go) to make it malleable. If your unit is warped at the top of the filter
opening, that\’s a good place to start as that\’s the easiest area to
Before you start, push on the warped area to move it back into
place – You are only doing this to get a \”feel\” for how much
resistance the plastic has at room temperature -> read on…..
Heat the
plastic, one warp at a time, with the hot air gun. You want to heat the
warped section AND a few inches past the warped area. Hold the gun about 2
or 3\” off of the plastic and KEEP THE HOT AIR GUN MOVING. You don\’t
have to move it fast, just keep it moving over the warped section (plus a
little extra). Don\’t worry about heating the inside of the filter box.
It will work just fine heating it only from the outside.
In about 2 to
5 minutes (this depends on how hot the gun is, how much area you\’re
heating, how close you\’re holding the gun, yada yada) the plastic will
be soft enough to flex easily. At the proper temperature, the plastic will
have less than half of the original resistance it had at room temperature
when you press against it to reform it. If it just pushes into position
with absolutely zero resistance, that\’s a little too hot. Not a big
deal, but you really don\’t need to get it that hot to reform
While wearing the kitchen mitt, reform the plastic to where it
should be. You may need to hold it into position for a minute while it
cools. If it keeps returning back into the old deformed position,
you\’re not getting it hot enough.
No need to quench it in water.
Air-cooling is recommended. In a minute or so it will be solid enough to
hold it\’s shape.
The small flange around the opening will most
likely need straightening as well. It tends to \”relax\” when heated to
a malleable state. Just push it up into the 90-degree position as the
plastic is cooling.
3 – Now do the other warped sections, one at a
Easy huh?
Here\’s the cautions;
* If the plastic
turns shiny and looks like road tar it\’s way, way too hot. You’d
have to really try to get it that hot, though.
* Most beginners at
plastic work are too cautious and never get the plastic hot enough (pay
attention to that statement)
* Plastic holds in heat for several
minutes. Even after it cools enough to hold it\’s new position, it\’s
still hot enough to burn you. If you burn your tootsies, don\’t say I
didn\’t tell ya.
* These soft plastics are very easy to work with.
As with all things mechanical, take your time and don\’t force it. If
you make a mistake, just reheat the plastic and start
One last thing – Judging from how the airbox warped,
I\’d guess (and I gots an education, so dat makes this an educated
guess) that apart from the heat, the singlemost contributing factor to
airbox warpage is overtightening of the hold down screws. That puts too
much pressure via the seal on the unsupported sections of the air

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