47 replies to this topic

[Saber]

I'm pretty sure my front bolts have worked loose again. I need to sort them out this weekend. Can anyone give me the exact spec of the bolts I need to buy? I would prefer the stronger ones.

Also, and this may sound dumb, but how many bolts should I be changing to make sure all 4 corners are safe?

Does anyone know if the bolts are the same as on the elise? And where I can get some from? Do eliseparts do them? (I know I could ask them but I'm not sure if I know what to ask for!)

Cheers chaps

Well, you need the same size bolts obviuosly (M10 x 50, I think it was ), just in a higher strength grade to cope with the higher tightening torque. The standard bolts are apparently of strength grade 8.8. I would suggest, you buy some 10.9 or 12.9 bolts AND follow the above mentioned advices for assembly, tightening to 60 Nm (even if using 12.9 bolts).

The strength grade is usually indicated with numbers on the bolt head - it does not have be to socket (umbraco) head bolts - hexagon or torx head bolts will do it as well (provided that there is enough space for the larger bolt head and tool bit).

It seems 8 bolts (2 per corner) are what need to be changed. NickB777 stated that Eliseparts had some M10 x 48 mm bolts (10.9), but you can get the right bolts from almost everywhere. Your local "building shop" might even have some, they are pretty common - and like I said, it doesn't matter whether it's 10.9 og 12.9 grade.
E.g. they have some here:
http://www.namrick.c...PTTID=1&PCID=10

Might be a good idea to get some plain washers and some threadlocker (medium strength, like Arno suggests) a long with the screws.

Hope you find them bolts!

Edited by Saber, 17 March 2005 - 04:36 PM.

[barrybethel]

Thanks Saber, you're a gent. I will be going to the lotus show at Donnington so hopefully I can get some from eliseparts there.

[Marco Polo]

I'm pretty sure my front bolts have worked loose again. I need to sort them out this weekend. Can anyone give me the exact spec of the bolts I need to buy? I would prefer the stronger ones.

Also, and this may sound dumb, but how many bolts should I be changing to make sure all 4 corners are safe?

Here are the complete drawings...





So 8 bolts all in all... (Front #11 x 2 & #12 x 2, Rear #5 x 4)

Note the 2 specs for bolt #12 (Front).... I don't know why....

I can look at mine only next Saturday (my car is in the body shop for a surprise)

[roxteddy]

I'm pretty sure my front bolts have worked loose again. I need to sort them out this weekend. Can anyone give me the exact spec of the bolts I need to buy? I would prefer the stronger ones.

Also, and this may sound dumb, but how many bolts should I be changing to make sure all 4 corners are safe?

So 8 bolts all in all... (Front #11 x 2 & #12 x 2, Rear #5 x 4)

Note the 2 specs for bolt #12 (Front).... I don't know why....

marco polo

I suspect the reason for two differnt bolts listed at 12. is to do with the number of camber shims fitted..... so if you have a lot of shims you would use the longer bolt... fewr shims use the shorter bolt.

[roxteddy]

Saber I registered for this forum mainly to say HUGE thanks for such an excellent write-up, otherwise i would probably just have continued to lurk as an observer. So very many thanks. One question tho'..... or challenge i guess..... If you use grease (eg Molybdenum etc) on the threads where it is not specifically recommended by manufacturer, you will get some hydraulic pressure during the pretensioning that has not been accounted for in the recommended setting. Won't this mean you will actually be torqueing > 45Nm even when your torqu wrench is set to 45Nm etc.....

[Mark A]

Where to start. 1st up using a 12.9 grade bolt on a suspension component is not a good idea, and it is something that no vehicle manufacturer does. Most bolts are 8.8 grade or 10.9 in some instances. The relative forces within a suspension are not the same as would be seen in a standard joint and despite all the knowledge and experience design engineers have nothing is signed off for use without adequate testing. All suspension systems are extensively tested on vehicles and test rigs, usually with greater inputs than will be seen by 99% or road users. This is to ensure all components and bolts are strong enough. The actual bolted joint also has lots of testing to ensure the correct torque is specified. Similarly increasing the torque without knowing EXACTLY the material specifications used on all components, hub carrier, shims and steering arm, means that you could end up yielding one of those materials, yielding just one of those parts means that you will end up with a reduced clamping force, despite the correct torque being applied, which will ultimately end up with bolt loosening, or if you use loctite on the threads, the clamp load reducing, this will result in slipage between the parts and with your more brittle bolt it ending up snapping. There are a multitude of tests required to sign off a clamped joint by a manufacturer and especially in the suspension system where a bolt breakage or loosening is a grade A failure (ultimately resulting in loss of vehicle control). The torque range is rarely based on the standard for a particular bolt specification. I'm guessing from comments in this thread and those elsewhere that the cars which have had a problem have probably had the bolts removed and retightened at least once or twice after the orginal build of the vehicle, as such there are numerous possibilities which can be applied to what has actually caused the problem. The usual largest contributing factor is usually overtightening, you torque them up and give it those extra few tweeks 'just to make sure', those extra tweeks could over stress the bolt resulting in the failure, or yield one of the materials resulting in a loss of clamping load. But even with the correct torque anything between the mating surfaces, corrosion etc can cause the same effect. Similarly making sure the threads are clean as and foreign substance on the trads can mean you actually achieve the required torque due to increaded friction in the threads rather than clamping force. In the 3rd picture posted by Marco Polo a loss of clamping load resulting in slippage between the parts is what has caused the bolts to bend like that. Personally I have never fitted upgraded bolts to any of the Elises or Exige I have owned and despite numerous trackdays (approx 50 between two cars over the last 3 years) I have never had an issue (and the Exige runs very stiff springs and dampers, Nylatron bushes and Yoko AO48's and it gets pushed very hard). By checking the mounting surfaces, and torquing correctly (I own a calibrated torque wrench which helps) you should never have a problem.

[Saber]

Saber

I registered for this forum mainly to say HUGE thanks for such an excellent write-up, otherwise i would probably just have continued to lurk as an observer. So very many thanks. 

One question tho'..... or challenge i guess..... If you use grease (eg Molybdenum etc) on the threads where it is not specifically recommended by manufacturer, you will get some hydraulic pressure during the pretensioning that has not been accounted for in the recommended setting. Won't this mean you will actually be torqueing > 45Nm even when your torqu wrench is set to 45Nm etc..... 

First off: Thank you for the nice words

To answer your question:
Yes...(and no)
You have different tightening torque values depending on the type of screw material (surface treatment), thread, type of thread lubricant, threadlocker etc.
What you probably mean (and you're correct ) is that, when using greased threads, you will get a greater clamp force (screw pretension force) for a certain tightening torque, because of the lower friction caused by the grease.
Most of the tightening torque (approx. 80-90%) is used to overcome friction, when reaching the required bolt pre-load. Therefore, you would specify a LOWER tightening torque for greased threads than for un-greased threads, to achieve the same screw pre-load.
"Greasening" the threads lightly helps reduce pre-load "scatter" (right word, I hope - more consistent pre-loads) - in other words: STATISTICALLY a small amount of grease improves the pre-load precision (though there's a bit controversy on the subject)
However like Arno suggested, I would recommend using the specified threadlocker (!!!!!!!!) - I wouldn't recommend tightening the bolts without anything on, because of the above mentioned reason. It you tighten an UNgreased bolt to the manufacturer specified torque, the screw will most likely not reach the intended pre-load.

Edited by Saber, 21 March 2005 - 07:01 PM.

[Saber]

Hmm, I cannot edit my posts... I just wanted to edit the last line above to: "If you tighten an UNgreased bolt to the manufacturer specified torque, when threadlocker, oil or grease etc. has been specified, the screw will most likely not achieve the intended, correct pre-load."

Edited by Saber, 21 March 2005 - 08:55 PM.