[NZ] Mataro Road Hill Climb

[Stiggy]

Over the years all sorts of bolts have been used for kit car suspension and I am not aware of any bolt failures.
Westfield use 7/16th's and Caterham use 10 mm on the rear and 12mm on the front BUT, look at the page below from Caterhams build manual. The front lower bolt does not have a bracket to support it, just a rivnut.

[kiwicanfly]

Wow, surely it is more than a rivnut though? A welded insert of diameter equal to the inside of the square tube perhaps?

I take your point though.

In that instance, assuming an insert, the bolt would bend and thus be sacraficial probably imparting zero to minimal damage to the chassis itself.

Looking at the distortion I have on the rear mounts I am wodering if the damage there was caused by the tyre wall at Manfield in October. The distortion is reasonably equal to both mounts, it may have also been the cause of the intial cracking on the front mounts that I had spotted prior to this prang.

I am currently formulating a plan to straighten and realign the brackets, the plan has the grand title - "How the f@$k am I going to fix this?"

What does bother me though is that if I do make the mounts stronger it could lead to other damage, such as to the tubing, as the next weakest point is found

Which therefore adds further legitimacy to Stuarts suggestions.

Alternatively I could just learn to drive and stay on the road

[kiwicanfly]

Just downloaded the 192 page build instructions for a Caterham!

Of particular interest was the details of the kit contents and pictures of all the parts it sure is comprehensive though.

I wonder if the use of the fixing method was for impact protection reasons or simply part of the design in general

[mawdo81]

I'd want the weakest point to be the easiest to repair...surely a stack of bolts is cheaper and easier than full strip downs & re-welding...

Did you miss some gear changes, or just lose traction? There was one at around 56-59 seconds in where it sounds like the engine revs hard and quickly.

Best thing is you're safe, you can fix it and got a great time with cracking video. Worst thing is you didn't get the class title ;-)

[kiwicanfly]

I really don't think it is as simple as using kneck down bolts, the idea is sound but determining an applicable failure load requires way more information than I have access to.

If I was using the car only for track based races along with a team of design engineers that might be viable but I also take the car on the road, any failure there might result in carnage and legal action.

We could take a simple scenario and calculate the forces on the mounts from a frontal impact at 100kph and have the bolts shear at that point. However my impact was not directly frontal, the nose hit at an angle, the car was spun anticlockwise, then (I am guessing) the driver side wheel "hooked" the bank and the rest is history. Impact sped 23kph according to the dash but the rear wheels (thus speedo pickup) were probably locked but then again, if so, speedo should have said zero.

So given that the design failure in the paragraph above did not match the event do I redesign for this scenario?

Further to this I am pretty sure that my front mounts had weld cracks in them prior to this event, I noticed this the day before. So, in theory, I should have had a "bolt failure" prior to this event. When I hit the tyre wall at Manfield perhaps? However considering that same issue has arrisen on a number of Rockets that have not had impacts perhaps it was not one event that caused it which leads one to wonder where and when I would have found myself with only "three wheels on my wagon"

Anyhow a man is on his way, literally as I type, armed with a TIG welding set.

Details of changes to follow.

[kiwicanfly]

Another point against using a shearing system is the likely hood of both lower arm bolts failing together - zero.

With only one failure the other mount would see significant twisting, this may result in an even more difficult repair exercise.

[kiwicanfly]

Each of the mounts was adjusted with my new best friends - a 3lb club hammer and (discovered under a bench at work) a 2 foot long adjustable spanner.

The front driver side mount had to have radical surgery as well (this was the one that took most of the impact), I had to cut this with a hacksaw even to have a chance of making it close to true. You can see the cut and the alignment after much banging and levering.



Eventually I got all four mounts withing 1mm of a string line through the centre of the chassis which was good enough for me. However none of the mounts were in line to allow one bar to pass through front and rear, they appeared to be twisted slightly on the mounting plate.

These are the gussets added this weekend.

The gusset for the "split" mount was made deeper to reach the original gusset under the mount.




Passenger side, both of the top gussets are 50mm along the base so giving a much longer support length for the front.



Anothert gusset was added underneath each of the bracket plates to incease support there also, front.




Rear.




Final job was get a 'Can o' Red' and give them a spray. The paint was left over from the original paint job and a local supplier put some into an aerosol can for me. Match is nowhere near perfect and not shiny at all but it's better than bare metal and, quite frankly, I gave up on keeping it blemish free and polished the day I put on stick tyres!