For today's project, we're going to be looking at how a tire and rim seal air inside. If you've ever had a tire with a mysterious air leak and had the shop tell you that the leak is caused by the rim bead seal, this is what they were talking about.

Here's a tire and rim from a wrecked 2000 mercury grand marquis

This tire is junk because of a couple unrepairable gouges in the sidewall. So some destructive cutting tools were used to pull the tire off the rim

Here's the tire after it was cut in half.

On the surface, this may look like a nice 1999 crownvic wheel

But under different lighting, rust is visible around the rim flange where the tire bead normally sits.

Here's the rim with half of the tire sitting next to it

And the rim with the tire cross-section installed on it

Here's a diagram of how a steel belted radial tire is constructed

Here's an actual cooper tire cut in half showing how the tire seats against the rim flange

When the rim flange rusts like this, air can escape through the rust pits.

Closeup pictures of the rust around the rim flange

Crevice corrosion happens in this area because water gets trapped in between the tire and rim with no place to drain out.

Now that we've seen the rusty rim flange, lets try an experiment to remove all the corrosion.

First, use an electric drill with a wire wheel to remove the loose rust scale.

And start dissolving the rust with a phosphoric acid solution

The pink colored stuff on the rim is the naval jelly solution of phosphoric acid. The small bubbles in the gel tell you that the acid is doing it's job etching away the rust.

Here's the rim flange after several applications of naval jelly. The rust is gone for the most part, but there are deep pits in the metal where the rust pores used to be. Rust never sleeps and you want to get rid of it all to make sure it doesn't come back.

The active ingredient in naval jelly is phosphoric acid. Unlike other acids that eat away rust, this stuff for the most part leaves the uncorroded metal behind untouched.

For cleaning up rust, sandblasting also works nicely. It is a lot faster than etching rust with acid. But it does remove more "good metal" than the naval jelly method.

The big problem now is going to be figuring out what substance to use to fill in craters where the rust used to be. A coat of paint with some tire bead sealant on top might work.

On rare classic cars with rim flange rust this bad, you'll sometimes see restoration shops weld metal back to the rim flange and then turn the rim on a lathe. But this rim is from a high volume production car and replacement rims are plentiful at the junkyards. New replacement steel wheels are also still avaliable for the 1998-2002 crownvics from ford motor company too.

There was quite a bit of rust around the rim flange, but the steel is still reasonably thick in this area. So the wheel still has a good amount of mechanical strength left to it in the rim flange area. Sometimes, you'll encounter rims that are so severly corroded that the flange area has the strength of tin foil.

Getting all the rust off this rim took a few days, the process I used was:
-Apply naval jelly to rusty metal
-Let rim sit overnight with acid solution on rusty metal
-In the morning after the naval jelly had dried, use a wire wheel on an electric drill to remove the rust that the naval jelly had loosened up
-Then reapply the naval jelly to start the process all over again

Here's the back of naval jelly bottle

Despite what naval jelly's material safety data sheet (MSDS) may imply, the substance is relatively safe to handle. But it would still be a good idea to use the substance outdoors or in a well ventilated area to prevent the buildup of irritating fumes.

Wheel Balance Weights

Here is a wheel balance weight on the rim

The clips on these do not get deep enough into the flange area to cause any leaks

Valve Stem

Sometimes, you'll encounter leaks around the tire valve stem.

Here's a 2000 grand marquis wheel with the valve stem installed

A closeup of the rim from back showing the rear of the valve stem

The rim with the valve stem removed. Notice the new circular hole that didn't used to be there?

Here's the rim from the back showing where the valve stem would normally insert

There are some abrasion marks on the valve stem from where the hubcap was rubbing against it. The hubcap weighs a lot less than a steel wheel, so the two items don't always want to rotate at the same speed.

Tire Shop Air Leak Sealing Methods

Bead Sealer

Bead sealer is a black rubbery glue substance that is used to help the rubber tire seal to the metal rim. It will also fill in minor imperfections in the rim. And will help keep small debris like stones from getting in between the tire bead and the rim flange. It does however make the tire a little more difficult to get off the rim during service.

Air drill

An air drill with a variety of attachments are used to clean up the tire bead and the rim flange area

Wire Wheel

On steel wheels, a wire wheel is usually used to clean up corrosion.

Scotch Brite Pads

On aluminum wheels, scotch brite pads are usually used to clean up corrosion. Aluminum is softer than steel and scratches relatively easy. These scotchbrite discs are also sometimes used to clean up the rubber surface of the tire bead too.

Wire Brush

Without power tools, you could use a wirebrush on the steel wheels instead. Rust cleanup will take a little longer with this tool.

Bead sealer + Rusty Rim

A common practice to seal up tire air leaks on steel wheels around the bead area is to remove the loose rust scale with a wire wheel. Then coat the polished rust with bead sealer and install the tire. This method did get the really rusted rim pictured above to hold air reliably for over a year. Unfortunetly, rust never sleeps and that wheel developed air leaks again requiring the tire to be removed from the rim to "clean up" the bead area yet again. There's no perfect solution besides replacing a rim with a new one once the flange is rusted this badly.

Do It Yourself Tire Leak Repairs

You'll sometimes see the do-it-yourself crowd install large quantities of tire sealer via the valve stem in an attempt to stop bead leaks. This stuff has a poor success rate at repairing air leaks around the tire bead. It does however make a real mess in between the tire and rim. And it will also throw off your wheel balance.

Other Notes: