S2 rear upper plinth bolt failures ...

[robin]

I posted this on S*LOC as the LOT racers hang out there, but forgot to ask the same question here:

"There were two such failures at Silverstone yesterday, and my S2 135R suffered the same failure at Knockhill recently.

Maybe it's a coincidence, maybe not.

Question #1 - anyone got any ideas about why these bolts failed in such a catastrophic fashion?

The two cars yesterday would obviously have been apart a few times for camber adjustments as they're both race cars, but AFAIK my rear camber has never been adjusted since the car was new (I measured it once and it was fine) so I am 95% sure my bolts and joint were as they were when it left the factory.

Also, the 135R ships with A048R tyres, so I assume that using R-type tyres in itself should not be an issue.

Perhaps these bolts need to be removed and replaced once a year?

Question #2 - does anyone know for sure (no guesses, please) what type of bolts these are so I can stock up on a suitable replacement bolt. "

Full thread:

http://forums.seloc.org/viewthread.php?tid=124321


This reply seems to be the best explanation of why they fail and what to do about it:

"main reason they have issues is that they are not loaded in a convenstional manner...

the main load they take is the balljoint plinth trying to twist off the top of the upright, so the bolts are being bent...

the surface area of the plinth to upright is all that's acting against the load applied, and it's a relatively small area...

this is made worse by camber shimms, this just increases the 'joints' between the plinth and upright.

with hard race use, they should be checked every event, and certianly every time that corner takes a knock. Now, I know there are resons for NOT using 12.9 bolts, but I do, and change them at lest 2-3 times a year.

worth noting that it's the same issue with the front steering arm bolts... (this is one of the reasons for the design of the EP steering arms having a MUCH larger surface area to the upright to spread the load)"

Does anyone have any other views ...

Cheers,
Robin

[Stephen]

Robin,
Could it be that the alloy hubs have a flatter surface than the steel ones?
also, if the shims are properly fitted and torqued then they should make no difference as they would in escance form a solid block.
one piont to note is that if the ball joint leg contacted withthe casing then all sorts of funny loadings could occur. The S2 has i think longer shocks which may be a factor(guess)
another point is that the alloy hubs may be stiffer as the thread goes into a much thicker cross section tan that on the steel hubs.

2p

stephen

[tenkfeet]

Were they all LH rear failures and how many times had your car been on track ? The slightest movement in that joint is going to fatigue the rather long bolt .

Have you approached Lotus? Its very worrying .

[Stewart]

Question #2 - does anyone know for sure (no guesses, please) what type of bolts these are so I can stock up on a suitable replacement bolt. "
every time that corner takes a knock. Now, I know there are resons for NOT using 12.9 bolts, but I do, and change them at lest 2-3 times a year.

I know that when I had my geo done by MH Engineering, Mark was keen to upgrade my bolts as he was aware of some failures.

Sorry, I am not sure what specification he used but I am sure if you were to call him, he would give you the info http://www.mhengineering.co.uk/

[robin]

I think the issue with the shims is that as they don't have any lateral support for the bolts, the clamping force has to be higher to achieve the same resistance to motion (try it - if you squeeze a thin block between your palms and get someone to try an pull it out, they will have a harder time than when you squeeze a thicker block).

However, I think the main issue in production is just getting the preload right there are too many variables (maximum bolt preload cannot be exceeded, thread friction is variable, torque wrenches aren't that accurate).

I'm going to pop in to MMC this morning to take a look at it, and will talk to them about how often this happens, in their experience.

Yes, they're all LH rear, but that's probably because the circuits are clockwise, so those are the bolts under load at the fastest corner. I'll take the RH apart and see if there is any evidence of failure.

As to the movement/bolt length issue ... as I understand it, any movement in that joint would lead to failure irrespective of bolt length. The movement would cause a continuing loss of pre-load (just by grinding the faces if nothing else) and eventually the bolts will be left to operate in shear - no matter the bolt, this cannot be sustained for any length of time?

Cheers,
Robin