Yesterday i found that my lower front wishbones has been bent. Both has been bent slightly backwards. The paint has cracked and the castor angle is almost negative.

I have the early MK-ones (the ones on page 172 in the book). These has been discussed here earlier so it was not so much of a suprise, but i tought that they would last a bit longer.

I have been in contact with MK sportscars about this issue (erlier), but the only thing they could do was to sell me a set of new (with different design) as they are not the same company as MK-engineering that made my wishbones.

However, now i need plans for new ones. Does anyone has plans on wishbones that will fit a book chassie and maxi ball joint?

I will take a picture to night.

Maybe - but MK Engineering still exist!!

Don't know if Martin would be able to help...

How long ago were they purchased?

http://www.mkengineering.co.uk/start.htm

Cheers
JC

I bought the kit for about four years ago. I haven't contacted Martin but maby I should.

As I wrote in the previous message, this was not a big suprise. If I had known what I know today I would't bought the wishbone/kit in the first place.

This time i will weld my own, so it gets done properly.

Hi probably best to make your own as you say as the new improved ones supplied to the uk locost racers also only last a short time.
cheers matt

quote:

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Originally posted by procomp
Hi probably best to make your own as you say as the new improved ones supplied to the uk locost racers also only last a short time.
cheers matt

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I Just got a positive reply from Martin Keenan.
I will tell you more as soon as we have worked out the details.

As of now, the problem seems to be solved. :-)

MK engineering has offerd to exchange my wishbones to a pair of new ones free of charge provided that i cover the postage both way.

I have sent my falty whisbone (he just needed one) to him, and he will send out the new ones the same day my arrives.

I think this shows that MK Engineering really care about the customers.

top result.
Biggets reason I chose to build an MK was all the good things I have heard about them tbh
Pez

quote:

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Originally posted by Pezza
top result.
Biggets reason I chose to build an MK was all the good things I have heard about them tbh
Pez

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Hi as said tho the all new improved ones are no better and have still failed within 10 laps of brands without hiting any kerbs.
cheers matt

My new wishbones are on the way. Just got a mail from MK engineering about it. I even got some pics.

I must say that Martin Keenan is a top bloke.

My wishbone has arrived!

The weekend is saved!

Calculating the bending moment for a 700Kg car at a 3g bump
=( Car weight / four wheels * lbs conversion * 3g ) * inches from pivot to spring mount / 2tubes
=(700/4*2.204*3)*4.3*0.5

outer dia = 0.75
wall th = 0.063
stress is 115328
steel yield strength is 50000 psi
reserve = 0.434

outer dia = 1.00
wall th = 0.063
stress is 60842
steel yield strength is 50000 psi
reserve = 0.822

for a pivot to spring mount distance of 2.0, similar to a Caterham. Note that Caterham probably use better steel than something with 50000psi yield.

outer dia = 0.75
wall th = 0.063
stress is 53641
steel yield strength is 50000 psi
reserve = 0.932

outer dia = 1.00
wall th = 0.063
stress is 28298
steel yield strength is 50000 psi
reserve = 1.767

Take a look at those numbers. Less than 1.0 is a bent tube though you could probably go to 0.8 before you noticed.

At 0.434 the only thing keeping the tubes straight is the reinforcing plate and the stiffening effect of the spring and ball joint mountings.

The real problem is the distance between the lower bal joint and the spring pivot. Look at the figures for the Caterham value (I don't know what tube size they use but I've done a quick check of the distance)

Another problem is the lack of a true V shape which puts the tubes in bending on braking. The arms don't point at the ball joint centre, take a look at a proper racing car to see a true V wishbone.

The tube isn't big enough, the shape is wrong and the joints are too far apart. That's it in one sentence.