Jacking at the cruciform - right or lucky?

[Roadsport06]

CC, could you post up on how to do this simple thing of jacking up our cars in prep for axle stands. There are conflicted views.

Thank you

 

BRG and Yellow nose now with added brooklands

[andy couchman]

I just blow up 200 helium baloons and attach them to the rollover bar.

 

...if you see a 7 at 35,000 feet can you kindly point it back home. Thanks.

 

Andy

[Dave Rothwell]

I use two small trolley jacks and lift both front wishbones in parallel an inch or two at a time, then put the axle stands underneath the car when it is high enough

 

I place wood blocks under each bottom wishbone front to back and then jack under these

 

daveR

 

Member 6790

Superlight 0075 - K7 LYT

 

Edited by - Dave Rothwell on 17 Mar 2009 13:29:09

[Normans_Ghost]

For those who still insist it's OK to lift the car on the centre of the cruciform you should be aware that you are likely to fracture one of the welds at the end of one of the ends.

 

It may not be so bad on a K series but a VX or Xflow is a lot of weight on welds not designed to take stress in that direction (outwards).

 

^{Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here}

You and your seven toThe French Blatting Company Limited

[john g]

Roadsport06 has the correct answer 😬

[Normans_Ghost]

You are of course correct. I've asked.

 

^{Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here}

You and your seven toThe French Blatting Company Limited

[rj]

I've seen a new factory build car with clear indication of having been lifted there.

[Reg]

What, a bent cruciform 😬

 

Reg Marjason

Silver 1800 K-series Roadsport C7 SEV

www.marjason.co.uk

[Normans_Ghost]

It's not bending that's the problem, it's the welds fracuring as they are being pulled sideways.

 

^{Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here}

You and your seven toThe French Blatting Company Limited

[RichardUSA]

I don't see how there would be any difference in the forces imposed on the outer welds whether the lift is placed at the center of the cruciform or in it's final state on jack stands. Either way you transfer roughly 1/4 of the weight of the car each way across the member to the side frame. The outer connection/welds must resist this shear force. If the main cruciform tube deflected (bent) significantly I could understand how it might result in added stresses on the bottom welds - to say nothing of the tube itself. But whenever I've lifted the car I don't observe deflection in the cruciform tube which means it is transfering the load the same way (horizontally across the tube) as if the jack was closer to the side.

 

Regardless I've always been more concerned about the tube not having sufficient capacity and might deform so I'm at least going to put something substantial to distribute the force more uniformly across it's width. This should also resolve any other forces that may be acting on connections. (I'll also put the issue to one of the structural engineers at work since they are pretty bored these days.)

 

Still waiting for CC to jump in..................................................................................................................

 

BASIC TECH INFO: 2004/9,000 mile Cat w/Zetec SVT, widetrack, DeDion, 5 spd/3.62, 15-CR500's

[Normans_Ghost]

Richard, you are placing the weight of the front of the car on 2 tubes which are welded (brazed) at the ends. The force is attempting to bend the tubes which, in turn, will shorten them. The pressure is therefore on the tube to be pulled inwards to the middle.

 

I have seen lots of 7's with jack saddle marks on the cruciform and, when tapped, the joints are fractured but in place. Unless you look for it you won't see it.

 

Common sense tells me to jack where all the tubes and members join - under the towing eye. As long as the car is placed on axle stands under the lower wishbones the chassis will not twist.

 

Maybe I should put this another way. Would you fix a tow rope to the middle of the crufiform and tow the car from that point?

 

^{Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here}

You and your seven toThe French Blatting Company Limited

[Gambo]

Well my two penneth, I used to jack mine up on the rail Behind the crucifix. that has two diagonal braces comming down from the top rails of the chassis. My little brain worked out that the loads would be shared between the two welds at the end of the rail, Pulling the braze joints, and compressing the joints on the top rail.

[sjmmarsh]

Don't use a block of wood to protect the paintwork/spread the load. I used to do this (jacking at the cruciform) until the wood slipped and the steering rack bridge landed on the jack.....

 

Bruce at Arch knocked it back into shape for me.

 

Steve

[RichardUSA]

Screw it all I'm digging a pit in the garage. Always good to keep the wife nervous.. 😬

Thanks to all for comments. 😶‍🌫️

 

BASIC TECH INFO: 2004/9,000 mile Cat w/Zetec SVT, widetrack, DeDion, 5 spd/3.62, 15-CR500's

[Paul Deslandes]

digging a pit was the best thing I ever did garage-wise. I fitted a Mech-Mate glass fibre liner and its fab. I managed to find a beam jack that straddles the pit - bought it for £50 from a local garage that was updating its equipment. It lifts across the front of the car and I can get all four wheels safely off the ground with a trolley jack at the rear. Great for doing the brakes.

 

 

[tweeky]

may be this on the FAQ`s need changing then here

 

Tweeky

 

In a purple haze

[Normans_Ghost]

I think that should be changed. Still no answer from Caterham but as the handbook says NOT to jack under the crucifix I would have thought that was sufficient for evaryone to take note.

 

^{Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here}

You and your seven toThe French Blatting Company Limited

[Bob Simon]

From the Caterham assembly manual, section 2 page 8:

 

Lift the front of the car

and place the axle stands at the outer ends of

the second chassis cross tube adjacent to the

rear mounting of the lower front wishbone

mounting, Fig 4 refers. If the car is raised on a

jack the jack should be placed under the front

cruciform ensuring that the powder coat finish is

protected.

---

[Tim Renshaw]

As I said in my earlier posting this refers to the bare chassis before the weight of engine etc is added so it is probably ok at that stage of the build, question remains whether it is still ok once everything else is in and it would be nice to have the definitive answer from CC.

 

It's Somewhat Vider and meant to be driven not polished!

[Bob Simon]

Sorry Tim, missed your post.

 

The build manual would tend to make one believe that once the chassis was full of parts, it should be rejoined with the floor using the same technique.

 

Someone close by, please give Caterham a bell. My current longitude makes it an International call.

[Normans_Ghost]

Bob, I've emailed them with a link to this, but no response yet.

 

^{Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here}

You and your seven toThe French Blatting Company Limited

[Dartmoor7]

The Owners Manual (NOT the Build Manual) for my 1994 car says to jack 'under the front crossmember immediately forward of the engine', on my car this is a tube perpendicular to the side rails with four slimmer diagonal braces to the side rails.

Is this what you are describing as the 'cruciform'?

The car has been jacked on this for the last 15 years without a problem.

[Atinod]

If it is not strong enough, it would seem to me to have been a simple design improvement to the chassis to add a strengthening plate at this point during manufacture, because it is a logical place to jack the car

[myothercarsa2cv]

Wherever you jack a car, unless you have a lift like my 2cv garage, is going to put stress on the chassis, surely?

 

(the lift at the 2cv garage is a flat plate with carpet on that lifts the whole thing in the air by it's belly - great for 2cvs, bad for rivets though... )

 

John

_________________________

 

Bugsy: '82 2cv6 (Back on the road!!! 😬)

Talloulah: '08 1.6K Classic (Grubby )