Magnesium Wheels.

I have mags on my 916. But for my 1198 I will hunt out some forged ones. I got my mags cheap but I sent them off to be examined and repainted. Theyre fine. I understand that I will have to repeat this soon. But after the last scally scaped the paint when putting a new rear on, I would have had to anyway. With forged I guess you dont have to worry about them quite so much.

 

Mine are early 1980's Dymag's - they still fetch a lot of money too - will have to get them tested but they are quite a thick H section and heavy compared to modern versions. Hopefully this means they are less susceptible to cracking!

 

Me personaly id want any used magnesium products tested before I rode on them.Dymag are back up and running or this company.

TPCS Magnesium and Alloy Refurbishing

 

There is quite a difference between wheels aimed at the race track and wheels for road use. If you compare the Marchesini offerings, the road wheels have bracing and are heavier to cope with the poorer road surface. Race wheels are very light but if you are only going to fit them to a track bike, once checked, there should not be an issue. I have late 90s vintage wheels checked by TPCS before refurbishing and they have been fine. Currently looking at a 2005 vintage set of Dymag carbon rimmed mag alloy wheels which are incredibly light but will go to TPCS before I agree to buy them. Andy

 

Mag is funny old stuff as one of the problems found by Dymag on my failed rear carbon wheel was that the magnesium hub had also corroded badly.Ive also heard from a guy that had the carbon rim/mag spoke dymags and the mag spokes cracked.Now Dymag use alloy hub on the latest CA5 carbon wheels.

I also have DP road type magnesium triple clamps on my bike.I will have to check with JHP next time its in for service on checking them.Not sure if you get them checked every couple of yrs or down to mileage or what.

 

I have the race version 5 spoke mags without the bracing. They are enormously lighter than the 3 spokers. Dymag checked and re-painted mine for me quite reasonably a few yrs back.

 

Mag wheels for the track are engineered lighter than the mag wheels for road. The track ones have a higher mag content in them, and the road ones are better protected in terms of corrosion dipping etc, and as Android has said, more bracing to satisfy due diligence and safety margins.

People just need to understand that track stuff is designed for the lifespan of getting through a season. Anything after that and you'll probably go for a redesign or a new part.

crack testing will only help so far, as will ultrasound, but all crack testing does is show up surface cracking that perhaps you could deduce permeate right through or whatever.

In an ideal world manufacturers would have each wheel tested like an aircraft wing section when its manufactured which in turn would then give traceability for future testing and historical data on the life of the wheel.
(put simplistically, you run a current across it and measure the current using it as a baseline. You can hen repeat the test say every year and compare results. If the current varies but a stated amount then you probably have a crack / corrosion in there - or in the case of the aircraft, a delamination.

Mag is also a superb sacrificial anode and about the only thing that doesn't make it corrode is stainless or titanium. Early in the production of carbon/ mag rims they used to put the magnesium hub right on the carbon, which caused them to corrode, carbon is very good at making aluminium and steel corrode as well.

so, make sure that your magnesium is being bolted to and with a suitable metal or in the case of carbon, a suitable barrier like a glass fibre ply or stainless shim.

One last thing, BST, martinis et al will all preach ISO and TUV numbers to you with regards to impact testing at the like. No one has put these wheels in an environmental test chamber like at Dunton- where for example a vehicle is exposed to maybe several years plus of accelerated ageing in all temperature extremes and UV conditions on a rig which shakes the chassis to simulate constant riding.

That shouldn't really stop you from buying any of them, and there's a lot of scare mongering and doomsayers telling you why you shouldn't. Like anything, as long as you know what you are buying then its not a problem.

Early Dymag stuff used resin transfer moulding technology - personally having done it on monocoques and chassis, I think its shit. Pre-preg like BST is far better.

These were a set of Marchesini wheels that had never been out of the box. - the classic eBay "paint started to blister, might need a respray)

Scraping away the paint layer we can see that the corrosion is quite heavy.






First step was in finding someone like TCPS above (who are ace) to refurb the wheels. This would eventually involve:
1) stripping old paint or coating off
2) crack testing
3) Blasting with Aluminium Oxide
4) Chromate dipping
5) Applying new finish.

the crack testing would only really show up cracking that wasn't immediately visible. I used a thermograph to validate my own testing, but I had access to a full NDT lab and test cell and rigs.

Once chromate dipped you shouldn't have that much of an issue anymore. Early Marchesini and Technomagnesio super lights were notorious, but that said they were proper lightweight wheels aimed at racers and race teams, and thus they did their job perfectly.

Risk of corrosion is higher on cast mag that forged. If mounting holes are threaded make sure they have a stainless insert in them for peace of mind. Other than that its a metal wheel like any other. if in doubt send them to TCPS - if they're that far gone you'll get a phone call saying they're in three pieces in the skip.

 

Two things:
Stainless and magnesium = corroded magnesium. Check the galvanic series.
Composite structure on aircraft is not subject to routine NDT.

 

I stand corrected Ricky.

We use stainless inserts on all our composite structures, but all our magnesium is rarely in surface contact being wrapped in glass.

How do you test for delamination in wings if I might ask?

We used such a method to test a nose box assembly that was brought into question- the process was brought to us from aerospace or do we were led to believe, it was similar to what Airbus use to test their wing sections for delamination.

Fascinating

 

Depends on what you mean by crack testing, MPI and dye penetrant for example only show surface cracks but xrays show through the whole structure!

 

Yes, but its hardly available to every well refurb merchant is it?

so who would I go to off the street for industrial radiography performed to MIL-STD-453 and MIL-STD-271, and ASTM specifications at LTI?

you could try this lot:
Insight NDT Ltd
InCon | Non Destructive Testing Specialists UK

might be worth calling them and seeing how much they charge.

Nothing is insurmountable but Nelsons question was as man off the street what does he need to know about owning a set of mag rims. There's no point banging on about x-ray if he can't ever get access to it or has to pay through the nose for it.

 

The point im making is that surface testing wouldn't be peace of mind for many when your life may depend on it. Personally I wouldn't use that a set of wheels that have only had a surface inspection as it does not guarantee the full structure of the wheel only the immediate surface. Ive no idea how available xraying wheels are to the man on the street as I have never had to. All the metallurgical inspection and testing ive done or been involved with was all industrial.