Corroded Cast Wheels

[Sgt.Cupid]

I'm about to fit a new tyre to a GS cast wheel and the bead seat has a few areas of the dreaded white powdery corrosion. Apart from the obvious air leak issues I'm more concerned how far the corrosion has travelled under rock hard coating BMW applied to the wheel from new.
As this is a winter/offroad spare wheel I'm not worried about cosmetics.
What I wondered is if anyone knew a way to chemically stabilise/neutralise this type of corrosion without resorting to a complete strip and refurb?

 

[Neil W]

Recently did a set of GSXR wheels with polished rim edges that were leaking and other than powder coating there is only one way to do it properly.............. take off the tyre and the entire area between and including the tyre seating area needs to be stripped back to solid shiny medal , either with a rotary wire brush or I grit blasted the area of the wheels.

Then spray with a couple of coats of a decent acid etch primer U POL or similar (in the past I've also used aircraft zinc chromate primer ) , once done it needs a coat or two of paint followed by a couple of coats of decent wheel lacquer.

Once hardened it will last for years

 

[Tractors are go]

Only safe way is total strip down and powder coating, a rapid deflation at speed is not conducive to clean underwear.

To do my Trophy front wheel was £40 for blasting/coating, £26 for new bearings/seals and £10 for tyre removal/fitting and re balance.

 

[Neil W]

Thing is with this type of corrosion , if it is going to lose pressure it will be unlikely to be rapid but it will be one of those pain in the arse 5 to 10 psi per day one that needs re-inflated every day

 

[Bendy toy]

I had my cast wheels powder coated. They looked slightly bubbled but having see the mess my engine front cover got into I didn't mess about.

The paint is incredibly hard. Grit blasting will chew away base metal before it shifts the paint. Get them dipped and powder coated at a car wheel refurb company.

For those in the area. For stripping, I used
Thyssen Krupp
Watling Street
Tamworth
County Staffordshire
B77 5BH
Phone 01827 281296

They strip anything up to car bodies so wheels are a simple for them.

Powder coating was done by CJ Ward Burton on Trent.

In Devon I used Wing and Son near Totnes http://www.wingspowdercoating.co.uk

There is also Spectrum Coatings Limited, BUTTLANDS INDUSTRIAL ESTATE Newton Abbot · 01803 813677 http://www.spectrumcoatingsltd.com

 

[Greenman14]

I had the same problem on a car wheel. The garage removed the tyre, cleaned up all the corrosion and refitted the tyre. It's been ok for over a year. You should get a 95% solution with emery cloth and hammerite.

 

[Sgt.Cupid]

Thing is with this type of corrosion , if it is going to lose pressure it will be unlikely to be rapid but it will be one of those pain in the arse 5 to 10 psi per day one that needs re-inflated every day

Agree with you, had this on car wheels before and it's a royal PIA. This is why I'm trying to find a quick fix before I fit the tyre without resorting to a full strip and refinish.
I found an interesting article aimed at the aircraft industry after a bit of googling, which seems to give a method for localised chemical neutralising/stabilising of this type of corrosion....
''Aluminum surfaces that are to be subsequently painted
can be exposed to more severe cleaning procedures
and can also be given more thorough corrective treatment
prior to painting. The following sequence is
generally used:
1. Thoroughly clean the affected surfaces of all
soil and grease residues prior to processing. Any
general aircraft cleaning procedure may be used.
2. If residual paint films remain, strip the area to be
treated. Procedures for the use of paint removers
and the precautions to observe were previously
mentioned in this chapter under “Surface Cleaning
and Paint Removal.”
3. Treat superficially corroded areas with a 10 percent
solution of chromic acid and sulfuric acid. Apply
the solution by swab or brush. Scrub the corroded
area with the brush while it is still damp. While
chromic acid is a good inhibitor for aluminum
alloys, even when corrosion products have not
been completely removed, it is important that the
solution penetrate to the bottom of all pits and
underneath any corrosion that may be present.
Thorough brushing with a stiff fiber brush should
loosen or remove most existing corrosion and
assure complete penetration of the inhibitor into
crevices and pits. Allow the chromic acid to remain
in place for at least 5 minutes, and then remove
the excess by flushing with water or wiping with a
wet cloth. There are several commercial chemical
surface treatment compounds, similar to the type
described above, which may also be used.
4. Dry the treated surface and restore recommended
permanent protective coatings as required in
accordance with the aircraft manufacturer’s
procedures. Restoration of paint coatings should
immediately follow any surface treatment
performed. In any case, make sure that corrosion
treatment is accomplished or is reapplied on the
same day that paint refinishing is scheduled.

And I also found fairly simple instructions for making the chromic acid, I can pass it on if anyone is interested.

Looks like an interesting way to do 'spot' teatment of the corrosion and then paint to seal it over.
I don't have enough time to try this at the moment, so I'll probably just rub it down and slap some smoothrite over it til next tyre change

 

[Bendy toy]

I could have done with this information before I had my engine front cover coated. The worst areas have bubbled as the oven heat "blew" the corrosion. The recurrence has not got any worse but maybe the chromic acid and some wire brushing would do the job.

 

[Sgt.Cupid]

Careful with wire brushes, they need to be brass for use on aluminium.
And if ur interested, Steve Grover at Motoscot does an exchange front cover, precoated in a nice black finish for £100 ish.

Oneplus 2 = my phone

 

[Neil W]

I could have done with this information before I had my engine front cover coated. The worst areas have bubbled as the oven heat "blew" the corrosion. The recurrence has not got any worse but maybe the chromic acid and some wire brushing would do the job.

That sounds more like the powder coater did not pre heat the part before spraying on the powder and baking, all alloy parts have minute casting voids and the heat of baking causes the air in the pockets to blow out (outgassing) ...... if the part is preheated then the powder is sucked into the open voids and when it is baked it will not blow out

 

[Bendy toy]

That sounds more like the powder coater did not pre heat the part before spraying on the powder and baking, all alloy parts have minute casting voids and the heat of baking causes the air in the pockets to blow out (outgassing) ...... if the part is preheated then the powder is sucked into the open voids and when it is baked it will not blow out

To be fair to the powder coaters, they did say that the corrosion pits were deep so outgassing could be a problem. I suspect the need to chemical strip the OEM finish is part of the problem. Corroded parts probably need to be dried in a warm oven for days rather than hot for an hour or two. The Yamaha parts were more badly corroded but the paint was easily stripped by shot blasting. The BMW parts have such tough paint that shot blasting does more harm than good.

 

[Bendy toy]

On another point, my GS cast wheels were power coated by CJ Ward in Burton on Trent more than 3 years ago. They did a good job and understand the issues with bike parts. However I had new tyres fitted yesterday and noticed a corrosion bubble (10mm dia) on the front rim. I'll clean it out and touch up the area. I believe it shows that corrosion on aluminium is very difficult to completely stop.

The wheels have been dry stored for at least a year in a garage attached to the house.

 

[Bendy toy]

I cleaned off the three bubbled areas with a small sharp screwdriver and rubbed in some alloy wheels cleaning solution. Dried and eat primed and touched in with black Hammerite.

 

[daytripper!]

Corrosion appears to consume the aluminium component (timing chest, cast wheel etc) so the longer the corrosion is left the more material must be mechanically removed to ensure the recoated part looks original / new rather than merely salvaged, or is there some form of filler (liquid metal) available? Also the term aluminium is probably a misnomer ie component will be a complex alloy but may be doesn't matter? I read somewhere that the Alclad skin of a Spitfire was aluminium alloy (to give required strength etc) with a thin outer surface of pure aluminium to form a corrision protective barrier.

 

[Bendy toy]

Rolls Royce developed the Dural alloy for aircraft parts. Much tougher than plain aluminium but harder to work with and even less corrosion resistant. Its likely they used plain metal for unstressed skins with Dural for spars and stressed skins.

 

[Bendy toy]

Corrosion appears to consume the aluminium component (timing chest, cast wheel etc) so the longer the corrosion is left the more material must be mechanically removed to ensure the recoated part looks original / new rather than merely salvaged, or is there some form of filler (liquid metal) available? Also the term aluminium is probably a misnomer ie component will be a complex alloy but may be doesn't matter? I read somewhere that the Alclad skin of a Spitfire was aluminium alloy (to give required strength etc) with a thin outer surface of pure aluminium to form a corrision protective barrier.

If you are powder coating you will need an electrical conductive filler. There is a product called Lab Metal but very not cheap and you'll only need a tiny bit and its got a short shelf life. Ordinary metal filled epoxy is probably not suitable for powder coat but should be fine painting. Just be sure the paint will handle the heat.