broken wish bone - crash

[Patrick]

Was a nice day so thought we'd go out do a bit of filming and take some photos. Towards the end Richard was filming me doing some drive bys. Went down the road to turn, round came back. All of a sudden crash and my from passenger side wheel is floating about. I thought the wing had come off but no, lower wish bone has torn in two just behind the ball joint.

Fortunately I was not going very fast and it was a quiet B road.

On the plus side I'm now a member of the RAC!

Has any one had a similar experience with their Sportster?

Here's some pictures:

Low res:
http://www.msportster.co.uk/data/p_wishbone001.jpg
http://www.msportster.co.uk/data/p_wishbone002.jpg
http://www.msportster.co.uk/data/p_wishbone003.jpg
http://www.msportster.co.uk/data/p_wishbone004.jpg
http://www.msportster.co.uk/data/p_wishbone005.jpg
http://www.msportster.co.uk/data/p_wishbone006.jpg
http://www.msportster.co.uk/data/p_wishbone007.jpg
http://www.msportster.co.uk/data/p_wishbone008.jpg

High res:
http://www.msportster.co.uk/data/wishbone001.jpg
http://www.msportster.co.uk/data/wishbone002.jpg
http://www.msportster.co.uk/data/wishbone003.jpg
http://www.msportster.co.uk/data/wishbone004.jpg
http://www.msportster.co.uk/data/wishbone005.jpg
http://www.msportster.co.uk/data/wishbone006.jpg
http://www.msportster.co.uk/data/wishbone007.jpg
http://www.msportster.co.uk/data/wishbone008.jpg

We actually got it on film, but the cars tiny in the pic:

http://www.msportster.co.uk/videos.asp

Also on there is the edited video of the day before the car broke.

[milliemarlin]

Re: broken wish bone - crash

Ouch!

What a wretched disappointment.

Any idea what caused it to fail? It didn’t look like it was under any great stress at the time.
Paul

[h_m_cumming]

Re: broken wish bone - crash

Hi Patrick, looking at where it broke makes me think that your bottom ball joint is too tight and it has tried to bend at the plate instead of at the ball. If you wash the dirt away can you see where the fracture started from?
What a shame. Has it done much damage?

[Patrick]

Re: broken wish bone - crash

The front part seemed to have some rust on it as if it had a fracture towards the front. Vibration from driving over time just fatigued the metal. I'm a bit disappointed as the the wing brackets had failed as well after only 50 miles, not so dangerous but this in on the other end of the scale - I am waiting on the new design ones form Marlin but won't get them till they unpack next year.

Cars only been on the road a month and has done 466 miles. I was accelerating up to speed on a straight road no pot holes or anything on the road.

Its bent the track rod and dinged my headlight has far as I've been able to see after a quick look last night.

I can't get through to Marlin land line - doesn't seem to be working at all so I've not been able to speak to Terry yet, but I have sent he an email.

Patrick

[h_m_cumming]

Re: broken wish bone - crash

Looking again at your pics. the design of the lower wishbone is not as good as the top. Where the radius arms are extended round the sides of the balljoint mounting on the top one and support it , the bottom one just relies on the strength of the plate to stop flexing. It would be much better if they were taken along the sides past the balljoint, if there is room, to give additional support.

[Patrick]

Re: broken wish bone - crash

Good news spoke Mark. I'm sending the lower wishbones back to him to inspect and he's replacing all the parts for free that have broken! He's not see one fail there before so I'm hoping it was purely a week piece of metal or weld.

[milliemarlin]

Re: broken wish bone - crash

Hugh makes a good point the design does look “sub-prime”.

For comparison my incomplete, and very dusty, Ford A frames do extend the tubes further.

Perhaps we should warn other BMW based Sportster owners to check for fatigue in this area.
Paul

[Patrick]

Re: broken wish bone - crash

I would certainly put it on the inspection list along with the wing carriers! Its a hard one as I had the car on axle stands and had a good look at it the day before. I even have photo's of the area from earlier in the day that don't show any obvious issues.

Given the Sportster has been on the market for 10 years and (so far) mine seems to be the only one that has had this fault I'd put it down to either weak material or a dodgy weld rather than a serious design flaw. However it does expose the weakest point of the design.

Patrick

[milliemarlin]

Re: broken wish bone - crash

In the good old days I used to drive a 15 year old MK I Cortina Estate. I was driving along happy as Larry when there was a loud bang under the bonnet and the engine started making a horrid noise and vibrating badly. It transpired that a flaw in the pressed steel cooling fan had suddenly given out. This caused about 2 inches from one of only two fan blades to fly off and dent the bonnet. On inspection the fan blade looked as though it had been sheared off with a guillotine. Very close inspection showed that about 10% of 50mm wide blade was slightly shinier than the rest. I will never know for sure what caused the 15 year old fan to suddenly break. The best theory I have heard was that when sheet steel is rolled the ragged ends of the steel can sometimes be pressed together hard enough not to show. Although the fracture can’t be seen the cold rolling process will not fuse the steel. Fatigue perhaps aided by corrosion over time gradually weakened the fan to point of failure.

Your photo wishbone004.jpg shows some signs of this type of failure. A dullness or corrosion showing across parts of the fracture. At first I thought that might be your problem. But a feature of the fan was the fractures straightness. Yours is clearly shaped around the highest stress points. So I guess any dullness was caused by fatigue over time.

Although the Sportster has been on sale a while how many of those have the BMW front uprights? BMWs were a later addition to the range. I have inkling that early BMW based units still used Ford uprights.

Paul

[dogoncrazy]

Re: broken wish bone - crash

I agree with earlier comments regarding the origin of the failure in as much that the oxidation shows that the material had a crack already present, the 'shiny ' metal is the fracture at the final stage.Unfortunately assessment is often difficult due to the one half of the fracture face rubbing against the other before complete breakage.My gut feeling is that the component is of insuffient profile for the possible loads it will encounter. Oh, and for my sins I am employed in a Metalurgy lab for Rolls Royce hence the interest!

[Patrick]

Re: broken wish bone - crash

Seems they've redesign the lower wishbone Jason (GreatOldOne) posted these pics on the Madabout-kitcars forum:

[GreatOldOne]Pics as promised:

http://www.jason.cundall.dsl.pipex.com/forpatrickwishbone1.JPG
http://www.jason.cundall.dsl.pipex.com/forpatrickwishbone2.JPG
http://www.jason.cundall.dsl.pipex.com/forpatrickwishbone3.JPG
http://www.jason.cundall.dsl.pipex.com/forpatrickwishbone4.JPG
http://www.jason.cundall.dsl.pipex.com/forpatrickwishbone5.JPG

The metal that the end plate the ball joint sits in is approx 6mm thick, and is bent at right angles at the end where the mounting point for the damper is welded on:

http://www.jason.cundall.dsl.pipex.com/lwishbone4.JPG
http://www.jason.cundall.dsl.pipex.com/lwishbone2.JPG[/]

Patrick

[ajgcurtis]

Re: broken wish bone - crash

hi patrick
looking at my sportster as you raised the alarm to cheek for any cracks!! I noted that the tubes extend further towards the ball joint allmost touching at the point of 8oclock/4oclock around the circumference of the ball joint weld. Its a 02 build reg'd in 03 BMW E30 and we have done 18,000 miles of fairly hard driving ,As for the wings the nearside broke on the Espana-Santiago challenge last september as did Peter Crouthers offside, also Mike Coobes at our meet in August
Regards Andrew

[Peterx]

Re: broken wish bone - crash

Andrew,
good to hear that you have done 18,000 mile without a failure.
Does your cars registration end in 53ABO? This car is featured on the Marlin build manual and has the 'old' type of e30 wishbones but before the damper mounting plates became extended triangular fillets. I wonder if it was this change that has created more stress at the line where Patrick's wishbone has cracked.
regards

Peter

[ajgcurtis]

Re: broken wish bone - crash

Yes the reg is hf53abo Very intresting to know its on the build manual I did not know such a thing exsisted !!

[Patrick]

Re: broken wish bone - crash

In this case build manual = series of photo's on a CD.

I've taken the wish bones off today, looking at them the week spot is right were it broke. There's a bend on metal plate right along the line where the tubes stop and the welds are. On the new design this bend is further back and the tube runs past it.

It could just be a dodgy weld and material that cause it.

I'm going to get the new parts crack test before I take the car out so that I can be sure the new ones are strong.

Patrick