Urgent check your Cosmic mk2 alloys

[griffipaul]

 

 

My Vitesse came with Cosmic mk2 alloys .. a real bonus as they were my in period favourite wheel , so lockdown job was to refurb them. Cleaning off paint at the moment , On the third one I decided to also clean up the centrebore....Horror of horrors cracked through in two places . Always thought the wall thickness between wheel nut counterbore and inner dia was thin anyway.

If you have Cosmic mk2 I advise checking them ..... I did not notice till cleaned up centre bore so look carefully,  I also need to go back and check others.

Like its a new set of something else even if the others are ok , as these things are rarer than rocking horse poo especially the 6J ones I have  , perhaps thats the way to go anyway if they are prone to cracking. 

Gutted.

,

[NonMember]

They are very thin there. I have Cosmic Mk4s (as Lotus Europa) on my GT6 and they're very thin there too.

I'm not actually sure how structural that part is. Could it be repaired by an expert alloy welder?

[Pete Lewis]

 as the ditch said    wheel meet again 

heck thats nasty , lucky  to spot it,

pete

[mark powell]

I'll have to check mine...

[Colin Lindsay]

17 hours ago, NonMember said:

They are very thin there. I have Cosmic Mk4s (as Lotus Europa) on my GT6 and they're very thin there too.

I'm not actually sure how structural that part is. Could it be repaired by an expert alloy welder?

Any chance that a metal insert might strengthen the area?

[Gary Flinn]

I have read about these possible cracking problems with that style of Cosmic wheel, presumably no way of carrying out any sort of repair with them being cast?

I've also read similar story's regarding Magnesium Wheels manufactured in the 1960's becoming brittle and dangerous.

Always liked the look of the Cosmics, it's a shame they aren't available new, I know JBW Wheels make Dunlop DI Replica's which are very popular, maybe they ought to do The Mk2 Cosmic's to suit Triumph & Ford vehicles, I'm sure they would sell well.

PS - Just noticed that JBW Wheels do supply a similar style wheel to the Mk2 Cosmic's but only in 10" and 15" 5 Stud 

Gary

 

Cosmic Mk2.html

[Pete Lewis]

didnt the old stuff used  to age harden  ??

way back  in the 60s we had gearbox cases made from electron ( magnesium based ) burns lovely when tooling failed on machining but old cases for recons were all crack and porosity checked due to aging problems that developed .

Pete

[Mjit]

Although thin and cracked it's not actually a load bearing part of the wheel or one exposed to the greatest forces (very close to centre so not moving as fast as say the rim).  As such it's unlikely, as it stands, to cause the wheel to fail.  It IS a risk though and if you decide to keep using them would need to be monitored.  A specialist should be able to TIG weld the cracks and then refinish the wheel/centre bore though I'd have thought.

ANY old aluminium wheel is a risk though, as our materials lecturer 'Dr Death' used to like to tell us.  Steel has a fateague limit.  Below that limit you can load/unload a piece of steel with the same weight and it just sits there doing what it's always done and staying as strong as it's always been.  Aluminium doesn't have a fatigue limit so every time you load/unload it it gets a little bit weaker until eventually it no longer has the strengh to hold the weight it always has in the past and snaps.  As a result at some point any and every aluminium wheel is just going to explode while you're driving along, causing a crash and killing you (he had an example involving death of serious injury for every material and mechanical property, hence why he was known as Dr Death).  It's also the reason aircraft parts are 'lifed', to say 500 takeoff/landings or 3,000 flying hours - so they get replaced before they get near the risk of them failing.

[griffipaul]

Thanks Mjit for taking the time to reply . I am sure we are all greatly reassured.

[griffipaul]

Ok , they need replacing then .

They were 6j , 25 mm offset with 165 tyres , and yes I know tyre is too narrow for wheel , was going to fit 175s providing they did not rub on inside. They were also mighty close to the outer lower wishbone fixing

 5.5 j will improve this 5 would be better

What was the orig spec wheel offset ? 25mm seems big especialLy with 175 tyres

Intend to use 175/70 tyres. With 5.5 j in preference to 5

Wheel offsets available are 5.5j -16 mm or 25mm depending on wheel design or 5j - 20 mm

With 175 tyres at 25 mm offset I will lose 5 mm clearance inboard and outboard  , with 16 mm offset will gain 4 mm inboard (good) but will lose 14 mm outboard with no tweak facility.

5j and 20 offset will keep the inner edge where it is but loose 10 mm outboard.

Looking back at past posts nobody qualifies tyre fitment success with wheel offset probably because they dont understand it or are aware or it.

Gary Flinn did say that 16mm D1 with 175/70  fitted but rubbed on bulkhead on lock , so I suppose you could say technicaly did not fit then there is also the issue of car to car variation , especially where body fit is concerned

 

I went through this when putting alloys on my tr6 , was asurred they fit no problem or yes I ve done that , was a pain , had go fit spacers at the front and double spacers at the rear and extra long studs.

YES PETE I WILL FIT M12 STUDS WHEN I CHANGE.

 

 

 

[daverclasper]

On 01/07/2020 at 12:21, Mjit said:

Steel has a fateague limit.  Below that limit you can load/unload a piece of steel with the same weight and it just sits there doing what it's always done and staying as strong as it's always been. 

Hi Mjit. Always wondered about our steel chassis, so that sounds good. Does that also include , that if it stretches due to load, over time, then will have reached it's limit (do I not have to be bothered about any further tub spread for example?).

Cheers 

[Nick Jones]

Unfortunately not uncommon on that wheel style when drilled to 3.75" pcd. The pcd is too small for the centre hole really, giving very thin sections.  Not the only alloys to suffer this either.

I ran this wheel style for many years.  5.5" mostly, which were fairly common.  They were always scarily close to the rotor wishbone bolts, to the extent that one with a slight buckle (and it was very slight) had to be used on the front as it would catch on the back when cornering.  6" are rare.  I happened across three of them for very little money, but one was cracked as pictured in the OP. 

Considered welding, but once I spotted the crack went all the way to the insert.......

.......... I preferred not to! 

Ended up using two 6" on the rear and the two best 5.5" on the front.  Were eventually replaced with a set of unused 100+ cross-spokes.

Nick

[griffipaul]

Can you recall tyre size you used on the rears want to use 175s. Presume this was on your Vitesse.

As you say there are poor design but nice looking

I think the other 3 are ok , but in reality , how much longer will they last and crummy 2nd hand ones are still more expensive than todays alloys.

Will sell them on to recoup costs I think. Going rate seems to be £ 100 a pop when they come up .

 

[Nick Jones]

I've always run 175/70s.  This was fine all round on the 5.5" ones but I think would have made occasional arch lip contact at the front on the 6" wheels.

The 100+ wheels I'm using now are 6" with ET13.  These represent pretty much the limit for standard arches with 175/70 tyres and do make occasional light contact with the arch lip at the front.

£100 a pop.......!  Blimey.... I struggled to sell mine in 2007 - nearly weighed them in!  Think I got about £120 for 6 of them..... with legal tyres.

Nick

[griffipaul]

Thanks Nick useful info

Based on the above then 175s on 5.5 with 16 mm offset should be ok as potential problems are on the outside, 

Whats your view of inner clearance with 25 mm offset.

Edited July 2, 2020 by griffipaul
Error

[SpitFire6]

16mm ET will put the wheels 4mm out more than OEM 20mm ET.

[Mjit]

16 hours ago, daverclasper said:

Hi Mjit. Always wondered about our steel chassis, so that sounds good. Does that also include , that if it stretches due to load, over time, then will have reached it's limit (do I not have to be bothered about any further tub spread for example?).

Cheers 

Apply a load that exceeds the materials elastic limit and you'll get a permanent deformation every time.  The difference between steel and aluminium I was referring to would be more like having two pieces of wire and repeatidly hanging/removing a weight from each of them. Assuming the weight's below the material's elastic limit both will get a bit longer under the weight but return to the original length when unloaded (no permanent deformation).  You can repeat that till the end of time with the piece of steel wire, but every cycle weakens the aluminium wide.  Basically steel has a fixed elestric limit but aluminium doesn't, it comes down little by little every time you load it and eventually it will drop below the weight you're hanging on the wire.

So no, this doesn't apply to tub spread.  That's a deformation where the metal's been taken past its elastic limit.  Take it past that limit again and it will  permanently deform again.
It does however mean you don't need to worry about your bonnet stay snapping at some point.  It goes through a load/unload cycle every time you put the bonnet up and rest its weight through the stay.  That weight is always below the steel's elastic limit though so safe.

Maybe a better example is why you don't normally get aluminium springs.  They are chuffing heavy so a perfect way to save weight, but also their whole purpose is to go through constant load/unload cycles.  A nice bit of spring steel will sit there for years happily taking the same load each time you hit a bump.  An aluminium spring would eventually pass it's fateague limit and snap though.  Not a major issue for things like paper clips, a bit more serious on a speeding car...  (That said aluminium spring HAVE been used, just generally in things like race cars where you're happy to bin the old ones and fit brand new ones between each session.  Not sure anyone is still using them as you can now make them out of carbon composits that while also life limited are even lighter and if you can afford to throw away aluminium springs you can probably afford to throw away carbon ones too.)