Rim tire leak repair

[MBGraham]

The rims on my 98 Mercedes started to leak a few years back. I had the old tires removed. After cleaning off the rubber sealant, I found several areas where the aluminum had bubbled and corroded. The interior of these rims including the bead area were factory coated with a brown paint/coating. Perhaps an epoxy. In sanding out the corrosion and cleaning up the beads seat, much of this coating was removed.

Problem now, is what to recoat with. Getting any coating to adhere to aluminum is not easy. But because the natural aluminum oxide protective coating has been removed, I believe that a coating must be applied. Just which one and how best to apply?

 

[TugboatEng]

Loctite 290 is the the correct solution here, better than OEM. It's recommended you heat but the product is so effective I don't think you'll need to. Degrease as best you can.

For application, brush it on wipe it off.

 

[CapriRacer]

I think Loctite 290 is for bolt threads, not tire bead seats.

I've used regular clear coat, but I made sure it dried for a long time before actually using the wheel. I'm talking a couple of weeks!

 

[BrianPetersen]

The tire shops have a special bead sealer to seal stubborn beads. I don't know what the stuff actually is, aside from being black goop that they paint on the bead area before installing the tire. Last set of tires that I bought for my car, I had to take a leaky one back, and that's what they did to fix it.

Another option is to go to a place that does powder-coating of rims. Normally that's for putting fancy colours on them, but you could either have them re-coated in something close to stock (or whatever you like), or ask if they can just do something to improve the bead seating area.

 

[TugboatEng]

Loctite 290 is also used for sealing porosity. It's in the datasheet. As it's not a costing it can't flake and peel off. It can be used in the bead areas. It would be superior for this application albeit expensive.

 

[MBGraham]

I see from the Loctite websites that Loctite 290 can be used to seal porosity. Here is a link to TDS:

https://krayden.com/technical-data-sheet/henk_loctite_290_tds/

They say that for porosity sealing, the items to be sealed needs to be heated to 120C.

In my case, although porosity could be a factor, main object of coating, is to protect the now bare aluminum from further corrosion.

I have had experience with the black gunk tire companies use. It works for a while. My experience is 2 weeks to 6 months.

I like the idea of powder coating, but not sure they can do just the bead area. The exterior surfaces of the rims are in perfect condition.

 

[TugboatEng]

Bare aluminum should hold up just fine inside of the wheel. It's the failed coating that causes crevice corrosion and exacerbates the problem.

 

[BrianPetersen]

Duplicolor aluminum wheel paint. Use as close to the colour of your rims as possible in order to not have to worry too much about overspray. Spray that in the bead areas, let it sit for a couple of days before you have the tires mounted.

I don't think you have to worry all that much about corrosion unless you are driving on salted roads in winter.

 

[EdStainless]

There are primer/paint systems for Al, but just having then blasted and powder coated is likely good enough. Are the wheels painted? The paint may not like the powder coat temperatures.
Sooner or later this happens to nearly all Al wheels, especially if you live in north or near the coast.
On my Volvo I wire brushed them clean and then used a clear coat in a rattle can that was designed for Al. I just did the bead seats. We waited a week to re-mount tires.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[MBGraham]

I have used silver Duplicolor on the exterior of rims on another car I own. But that was not over bare aluminum. Duplicolor say to use an etching primer on bare metal (no specific mention of aluminum which is harder to paint than most metals)

https://www.duplicolor.com/wp-content/themes/duplicolor2019/assets/documents/application-tips.pdf

There are paint systems for aluminum boats and sailboat masts. Probably also etching primer first.

Powder coating requires wheel in oven. That would entail refinishing entire rim inside and out. Might have been an option if I hadn't already bought aftermarket rims. Cost at least the same, I imagine.

By the way, being in Canada all wheel see lot's of salt so protection is needed even on inside of rim.

 

[TugboatEng]

How does the salt get inside the rim?

European cars have always suffered from porosity in the castings of the rims.

http://www.bavarian-board.co.uk/forum_posts.asp?TID=16418&title=porous-alloys

 

[BrianPetersen]

Salt water won't get "inside" the rim inboard of where the bead is actually sealing, but it will get into every crevice. The alloy wheels that I have on my own car is a set that I got dirt cheap because they needed refinishing, and the outer lips were in bad shape - on the outside because of curb damage, and on the inside because of corrosion. Tire shop still needed to goop up one tire where my sanding and repainting job evidently wasn't good enough for the bead to seal completely.

 

[MBGraham]

Tugboat, I presume you dont live up North
The lip of a rim and the bead area of the tire form a V-shaped valley. Water & salt are in close contact with the bead area for months each winter. Migrates into bead
My rims had typical white aluminum surface corrosion that grows outwards away from the surface. Very visible and preventing bead from seating. Now sanded smooth. Slight unevenness will hopefully be reduced by coating.

There were even some signs of corrosion inside the rim - probably from mpisture condensation from the air.

Looks like I need to use a primer and perhaps a hard 2-part epoxy or polyurethane coating as used on aluminum boat hulls and masts

 

[TugboatEng]

It seems that you have a plan. No need to say more. Carry on.

 

[Rex Hang]

According to me the simplest reason why your wheel may leak is the tire was not installed correctly in the first place.

 

[NormPeterson]

The rims on my 98 Mercedes started to leak a few years back. I had the old tires removed. After cleaning off the rubber sealant, I found several areas where the aluminum had bubbled and corroded. The interior of these rims including the bead area were factory coated with a brown paint/coating.

Do you remember paying attention to where those wheels were leaking back then? Bead seat solutions aren't going to be of much help if the barrel of the wheel is porous.


Norm

 

[TugboatEng]

Thank you Norm. I have friends that like German cars for some reason and they all know what they'll have to deal with the porous rims eventually.

Graham, internet fan forums tend to be sources of tribal knowledge and confirmation bias. You're in the wrong place to ask your question here but I hope you got the right answer.

 

[MBGraham]

Norm,
Yes I did test the rims before un-mounting the tires. I did not post the whole story in post #1. I used the bubble test and marked the rims where there were rim leaks. In each case, there was corrosion in the bead area. Back then I took some pictures (attached). I cleaned those rims up to bare metal. Then filled and coated them. Based on advice from a Mercedes "expert", I used a 1-part air cure polyurethane that is known to be effective when coating previously rusted steel. (An example would be POR-15) It forms a very hard coating. Problem is that it does not adhere to smooth surfaces. Requires some "tooth". I thought sanding with 80 grit would have provided that, but my coating did not adhere uniformly. Which it needs to do! I have installed aftermarket rims but would like to now restore the originals.

Tugboat says this was the wrong place to ask. Seems to be true, but I had hoped that I might find someone here in the automotive forum who could advise on the best coating to apply and the preparation needed. Perhaps the Chemical/coatings forum would have been a better choice. I have gathered some practical ideas from car forums. I have also found shops that will grit blast and coat; perhaps powder coat, but at a high cost. As Tugboat suggested, I will "carry on"

Thanks for the input. Every little bit helps

 

[TugboatEng]

Sorry, I was being a bit snarky. You've decided you want a coating so your best route will be to sand blast, apply a chromate conversion coating or chromate-free primer designed for aluminum. A coat of surface tolerant epoxy on top should seal everything up.

I would avoid powder coating as it tends to lift off the surface and form pockets that cause crevice corrosion.

Have you confirmed the wheel is leaking at the bead? I have to repeat, the German wheels in those years we're very porous, whether chrome or paint, once the coating fails they start leaking. I suggested the Loctite 290 because with will fill and seal the porosity very effectively and can't chip or peel off. If any pitting from existing corrosion is deep and preventing the bead from sealing, a metal filled epoxy should be used to fill the pit.

 

[3DDave]

I missed that these were aluminum - that isn't tooth that is the problem, it's that aluminum oxidizes very fast, forming a difficult to adhere to oxide surface, which as tugboat mentions, requires a chemical conversion coating in order to get most paints to stick.

I came across a youtube mercedes repair guy who was working out problems that chrome plating over aluminum produces. Chrome plating is not 100% barrier against moisture and is a dissimilar metal, so eventually any tiny imperfection becomes a corrosion point that progresses under the chrome, leading to a nearly irreparable leak path, short of electrochemical stripping and re-plating (probably far more expensive than the rims and likely to fail again just the same.) He was trying something called "miracle paint" in combination with a lot of sanding and multiple coats to seal off the bead area. However I see many are dissatisfied with "miracle paint" and it is likely because nearly no paint is thoroughly moisture impervious.

The same is likely for powder coat, which I have seen form a very durable cast-in-place layer that debonds when corrosion gets a start under it.

My gut feel is to try a polysulfide rubber over a conversion coat, but it's not a material I consider easy to make smooth after it cures, so significant practice or experiment may be required to get a decent surface finish.