Cracked rear AMG wheel, what to do?

[lynall]

I would get it welded, i had one welded on my discovery alloy and it held air and was fine all the while i had the car.

But if unsure just buy another wheel.



Lynall

 

[callahan]

It was suggested that a weakness in the wheel contributed towards my recent incident, here's a pic of the suspect wheel:

You don't want the rim to detach itself from the hub and spokes while driving I can assure you. If it were me I'd buy a replacement wheel although there is little to guarantee that it would be free from fractures or weakenesses unless bought new from MB or another supplier.

That is a scary thought, particularly as the car is used mainly by my wife to transport our 2 kids around....

I'll talk to BJV Eng about the welding option, but will also call a few more dealers to get some prices for a new wheel, any dealer recommended for keen pricing?

Cheers

 

[marty359]

My rear tyre kept going down last year, I took it to the place i get my tyres from to have a look and it was cracked on the inside and had shredded the inside of a new tyre with less than 200 miles use £420 for two tyres in two weeks

My mate who welds ally bulkers cut the cracked piece out and welded it back up for £30. Cheaper than a new wheel and ive had no problems since.

 

[Lugy]

As long as the welding is done properly I can't see any problem.

Get them to drill 2 holes at the end of the cracks, only if it's on the circumference of the rim, not the edge for potentially obvious reasons. This is reputed to stop the crack going any further, I've never seen any evidence of a crack coming back either way so who knows whether it does anything The theory's there though.

Although, realistically any ally welder will have done loads of wheels so should know what they're doing .

 

[wheels-inmotion]

We would have it welded. Providing this is done to aircraft standard it will be perfectly fine.

 

[callahan]

My mate who welds ally bulkers cut the cracked piece out and welded it back up for £30. Cheaper than a new wheel and ive had no problems since.

Is he anywhere near Saffron Walden, by any chance?

Otherwise, is it best just to go to my local quality tyre place?

Thanks again for all the replies.

 

[lynall]

The tyre place will cover their **** and just say you need a new wheel.
Google alloy welding in your area there will be someone, you really need it tig as opposed to mig welding.



Lynall

 

[EDZ649]

I wouldn't have a wheel welded, too much of a risk IMHO and I certainly wouldn't be happy selling the car on afterwards knowing a wheel had been welded.

 

[callahan]

The tyre place will cover their **** and just say you need a new wheel.

Lynall

That's exactly what they just said

It's surprising how this polarises opinion, but I suppose it depends on the quality of work done, which is difficult to assess without a recommendation in my area. I would be worried about future reliability and safety, particularly as I do like to 'push on' a bit....

The set of four here are still at a good price, but miles away. Anyone have an opinion on what they would look like on my car? I do love the ones that are on my car now: MERCEDES AMG ALLOY WHEELS on eBay (end time 15-Dec-09 18:53:36 GMT)

Thanks again.

edit: the Dronsfields' set are all the same size, so I'll leave them.

 

[Gridlock]

A properly welded wheel will be as strong as an unwelded wheel - put your faith in science

Just make sure you find someone competent, I second BJV Engineering having used them in the past (and the guy there drives VWs).

However, if it's going to be a an ongoing cause for concern for you, due to your kids etc, then buy a new wheel so you don't have to have it nagging at you. Have you tried German eBay? It's sorted me out very very well numerous times in the past.

 

[hotrodder]

Welding aluminium ALWAYS results in localised softening (partial to full anneal) of the area local to weld. Even if the God of welding is doing the work there is no way around this.

Doesn't automatically make it unsafe as wheels are obviously designed with a safety margin but a wheel is NOT going to be as strong as it was after welding.
Something else to bear in mind... aluminium (unlike steel for example) has no endurance (fatigue) limit.

There's at least three different alloys used for cast wheels and a couple used for forged wheels. Some are heat treatable and will be 'damaged' more by welding than wheels used in the 'as cast' condition. Forged wheels get a significant amount of their strength from the 'grain structure' imparted during the forging process. Welding is in effect casting so this grain structure is locally destroyed

 

[lxi]

A properly welded wheel will be as strong as an unwelded wheel - put your faith in science

and in the god of your choice.

Ask yourself the question - "why did it crack in the first place?". The molecular structure has altered and the wheel weakened - it's not like a piece of steel which has rusted.

It's like an iceberg - the bit you can see is but a small part of the entire object. Sure, you could have the visible crack welded but you cannot see (a) where the next crack might appear and (b) where the current crack really finishes.

I've had alloy items welded in the past in particular manifolds for Weber carbs. The weld itself was stong and would probably have lasted longer than the car. The original metal to which the weld was attached (yes, bits cut and / or ground out where the crack or break had been) did not as the visible crack was only a symptom of the overall weakness plus its molecular structure had been altered by the heat of the weld.

I'm not knocking those who weld allow for a living - there are some real craftsmen about, but a road wheel and the forces to which it is subjected is not something on which to take a chance.

Rhetorical questions - if you rode a bike, came off & cracked your crash helmet, would you be happy with an Araldite repair? If your seat belt had somehow been cut through would you be confident if it was sewn back together with even stronger thread than used for manufacture?

 

[callahan]

Well, I had a good chat with BJV Engineering and, as I'm not too far from there tomorrow, I'll take the wheel over to them and see what they think.

On the phone they were very confident that they could do it and the wheel needed refurbishing anyway

Thanks for all the help, advice and wildly differing opinions, I'll update again when I've seen them.

Cheers

 

[marty359]

Is he anywhere near Saffron Walden, by any chance?

Otherwise, is it best just to go to my local quality tyre place?

Thanks again for all the replies.

Looks like you may have it sorted now...but hes in Wisbech.

Pm me if you have no luck with the other place.

Marty

 

[wheels-inmotion]

Well, I had a good chat with BJV Engineering and, as I'm not too far from there tomorrow, I'll take the wheel over to them and see what they think.

On the phone they were very confident that they could do it and the wheel needed refurbishing anyway

Thanks for all the help, advice and wildly differing opinions, I'll update again when I've seen them.

Cheers

Wim's not to far from BJV (10 min) if you fancy popping in for a chat and cup of tea

 

[callahan]

Wim's not to far from BJV (10 min) if you fancy popping in for a chat and cup of tea

That's a very kind offer, thanks. Unfortunately I won't be in the beast, but my work hack instead

Might still be after a chat though as the C36 has started veering off to the left randomly (when accelerating anyway), even when I've just checked the tyre pressures....

Cheers

 

[callahan]

Wim's not to far from BJV (10 min) if you fancy popping in for a chat and cup of tea

Unfortunately I didn't make it yesterday as the snow was really bad when I was at BJV and I didn't want to get stuck when I should really have been at work....

I'll give you a call later to book the Merc in on tuesday, so I can pick up my wheel and then get the geometry sorted out in readiness for my Christmas travels.

 

[johnsco]

See my posts in a previous thread on weld repairs to alloy wheels.
Very risky in my experience.
I would not risk it.

 

[callahan]

See my posts in a previous thread on weld repairs to alloy wheels.
Very risky in my experience.
I would not risk it.

Do you have a link?

 

[Number_Cruncher]

I tend to share Johnsco's view on this.

In addition to the weakening in the heat affected zone, welds are always viewed as problematic, and high risk sites for future cracking by engineers who work with structures because;

1) The geometric discontinuity at the weld toe is a stress raiser
2) The welding process can introduce new defects into the metal, inclusions, blow holes and the like
3) The residual stresses around the weld can be both tensile, and up to yield stress in magnitude, which is ideal for crack initiation and growth.

Item 1) can be partially mitigated by good post weld grinding

Item 2 is a difficult problem, and only very thorough NDT inspection can clear a weld for service, or send the part back for re-work or scrap.

Item 3) can be partially mitigated by stress relieving heat treatments, but, this can ruin the initial heat treatment of the alloy - a point made very well by hotrodder.

This engineering level aversion to welding is so great, that on a rail vehicle, where cracks were found, and some stress analysis work was done, the conclusion was reached to simply grind out the cracks - no weld repair was done, because the analysis showed a weld repair would be more likely to provide a starting point for a new crack, and the part could work acceptably with no metal in that location.