I have a pair of original circa 1980 Dymags for my Project 1 bike, The front has been stored a long time with little or no paint and has gone all fuzzy wuzzy. Is there a good method of home cleaning / restoration prior to paint to get the bare magnesium back to a good finish or do I need aqua blasting or similar? I have special primer for the re paint just need to get them smooth and clean.
Magnesium wheels? Heat them to approx 500 degrees Celsius, that is sure burn to off any impurities. Pretty much burn everything else, too, once they start to combust
Normal process is to dip them in a mild caustic solution to remove paint, powder blast them to key the surface and passivate them to protect the surface from oxidising before re painting them. Having dipped and blasted them, it is usual pratice to carry out a dye penetrant crack detection before passivating. I guess all the chemicals are available and a home made blasting box as demonstrated on here can be made. To get it done professionally you are looking at about £200. I can recommend TPCS but you would have too post your wheels to him because he's in Melksham not too far from Bristol. Andy
Exige, if the paint is all fuzzy wuzzy you can safely say that underneath is some nice dust. Been there done that. TPCS is ex synagogue before they went bust so knows his stuff. You really want to stay away from grit blasting as the wheel tends to go bonfire night in you. The crack testing pre chromate dipping is all very well but only shows surface cracking. I used a combination of that and thermography to verify mine but if you know the history you should be fine. For the cost of the materials and the effort to do the chromate bath just send them to the man above, he's actually really reasonably priced.
My rear wheel is about 95% original finish with a few blemishes only. The front has original paint but has worn that thin it's almost not there - I dug it out to check last week and where I though it was going fuzzy was the thin paint - it's not bubbling at all and not fuzzy. I might try Por 15 on it and paint myself, already have the primer from the US. It is tempting to not have the hassle though as the cost mentioned above seems cheap!
I have to say alarm bells are going off in my head. Having used POR15 on a petrol tank, I'd do a little research before forging ahead. I know their advertising blurb says any metal including aluminium but Magnesium alloy doesn't follow rules and it would be an expensive error. Andy
Sev, Interested to hear more about thermography. In my experience, that would only be used on composite to find moisture damage. R
Ricky, I use to use it together with ultrasound to verify chassis monocoques and crash structures but I thought I'd use it to see if I could see more on my wheels. It still won't penetrate all the way through but for what I wanted it seemed to work. I knew the wheels were sound as they'd never been out of their box but I really wanted to see if there was any pockets within the casting and it seemed to do the job albeit in a primitive way. I spoke to a magnesium foundry about such things many years ago and they had a large ultrasonic bath which they submerged the magnesium into but even then they said that they were way short of the metal equivalent of an MRI.
