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Lotus Elan chassis - is it really that simple?

smart51 - 6/11/15 at 09:45 AM

Thieves tried to nick my trike, unsuccessfully, but they knackered it beyond repair. The insurers have inspected and valued it and the underwriters are considering sending me a cheque. Out of the blue, the Mrs suggested I make something else, once we've moved house. So I've got my thinking cap on to contemplate a new build.

I've been looking at the Lotus Elan chassis which is supposedly 5 times stiffer than a locost chassis and more than twice as stiff as Cymtriks mods. Which is surprising given how simple it looks. Are the sides of the engine bay really just a single sheet of steel, with a fold top and bottom?

Lotus Elan Chassis

britishtrident - 6/11/15 at 10:06 AM

On the Élan the body contributed a lot to the stiffness, the Élan was originally monocoque as on the 1950s Elite but the development engineers were having problems with the various mounting points in the grp hull so while Chapman was off somewhere don't deals and racing they added a sub-chassis to a development mule. The structure was probably inspired by that used on the Austin Champ.

Istr circa 1978 Spyder engineering built there own Sevenish car on the replacemet chassis they make for Elans but it is a spaceframe type and the body they made also braces the chassis.

[Edited on 6/11/15 by britishtrident]

[Edited on 6/11/15 by britishtrident]

Sam_68 - 6/11/15 at 10:10 AM

quote:
Originally posted by smart51Are the sides of the engine bay really just a single sheet of steel, with a fold top and bottom?

Short answer: yes.

It's incredibly flimsy, too - you can press against the metal of the main tunnel with your thumb and it will 'oil can'

IIRC it's 18 gauge steel with 16 gauge reinforcements.

The quoted stiffness is with the bodyshell fitted, mind you - the body contributes quite a lot - and it's not 5 times stiffer than a 'book' Locost; it's 4,300lb.ft/deg vs. 1,180 lb.ft/deg for the Locost, according to Cymtriks, so about 3.6 times stiffer.

Edited to add: the Spyder Silverstone chassis was quite different to the Spyder Elan tubular backbone replacement chassis, incidentally - it was much more of a full spaceframe, though it did also incorporate elements of the Elan backbone design (transmission tunnel and front corssmember, I think). This is the Silverstone chassis:

And this is one of their 'spaceframe' Elan backbone replacements:

The Spyder 'spaceframe' Elan replacement chassis is a lot stronger, but also a lot heavier.

[Edited on 6/11/15 by Sam_68]

steve m - 6/11/15 at 11:39 AM

The body on a 2+2 Elan flexed quiet a lot, even more so when it was detached from the chassis, and somewhere I have some pics of myself aged 19 changing the chassis on my 2+2 Elan, to a nice new galvanised one

Jacking the body up and off the chassis, was difficult, as the whole tub would twist to the extent that one corner would be free, but the opposite would bind, may be the baby Elan was better

In the end, I had to jack up the whole car about a 18" with the chassis attached,
support the body, and lower the chassis

So, my conclusion, would have to be, that the lotus back bone chassis, although looks fragile, must of been up to the job
But maybe in conjunction with the body made up the extra torsional strength, also on the 2+2 the sills had a steel girder inside the fiberglass (well mine were piles of rust !) not sure if the bay Elan did

steve

smart51 - 6/11/15 at 11:56 AM

quote:
Originally posted by Sam_68

quote:
Originally posted by smart51 Are the sides of the engine bay really just a single sheet of steel, with a fold top and bottom?

Short answer: yes.

It's incredibly flimsy, too - you can press against the metal of the main tunnel with your thumb and it will 'oil can'

IIRC it's 18 gauge steel with 16 gauge reinforcements.

The quoted stiffness is with the bodyshell fitted, mind you - the body contributes quite a lot - and it's not 5 times stiffer than a 'book' Locost; it's 4,300lb.ft/deg vs. 1,180 lb.ft/deg for the Locost, according to Cymtriks, so about 3.6 times stiffer.

I like the verb to "oilcan". I can almost hear the sound. As for the stiffness figures, that's what you get for believing what you read on the internet. Even so, it is stiffer than the locost chassis, even with Cymtriks' mods.

Spyder's website has pictures of a roll hoop and side bars and I was thinking of something along those lines. Perhaps with the side bars being higher up to offer some side intrusion protection. Some roll cage tube making a rudimentary space frame will no doubt stiffen the backbone further.

Sam_68 - 6/11/15 at 01:47 PM

quote:
Originally posted by steve m
The body on a 2+2 Elan flexed quiet a lot, even more so when it was detached from the chassis, and somewhere I have some pics of myself aged 19 changing the chassis on my 2+2 Elan, to a nice new galvanised one

Jacking the body up and off the chassis, was difficult, as the whole tub would twist to the extent that one corner would be free, but the opposite would bind, may be the baby Elan was better

Yes, the baby Elan was much better - at least in Coupe form; I've never changed a chassis on a drophead.

Having said which, I've changed a chassis on a Plus 2 and I didn't notice it as being anything like as bad as you're describing - but I had a fair gang of assistants, so maybe we were able to give it decent support. The Plus 2 was a heavy bugger, compared to the baby Elan, as well - two strong guys can lift an Elan shell, complete with glass and doors whereas I think we had 6 of us with the Plus 2!

The other thing that makes a surprising difference, apparently, is whether the dashboard is fitted. It's a stressed panel, bracing between the door hinge areas and the transmission tunnel, and adds quite a bit to the overall bodyshell stiffness. Ditto the 'strut brace' between the rear suspension towers.

But yes, all things told the Elan chassis was still a very elegant and minimalist design.The fact that it ran much softer suspension and higher profile (hence more compliant) tyres than is fashionable today, helped though. The Esprit started to suffer in its later years 'cos the chassis wasn't really up to the job any more, and that was a much heavier-duty backbone than the Elan's.

britishtrident - 6/11/15 at 02:42 PM

ISTR the baby Elan had some very minimalist steel stiffening in the sill --- whereas under a GRP sill the Plus2S had something resembling a tin-top steel sill to provide the jacking points and set belt mountings -- Chapman penny pinching zero corrosion protection of course.

The FWD Elan had a backbone + a perimeter box section similar to a Triumph Herald

steve m - 6/11/15 at 03:10 PM

I changed the chassis on my own! and probably got more help and interest from my Mother, than my Father,
bloody hard work, and did it on a sloping driveway, must find the pics !!

I imagine, but cant remember, that I removed all the interior, and dash, as to get to the bobbins would be impossible without doing so

steve

[Edited on 6/11/15 by steve m]

Sam_68 - 6/11/15 at 03:49 PM

No wonder you found it difficult, then!

You really need to be able to lift the shell vertically, so you'll have stood no chance on your own!

The 'pros' use jacks/lifts under the sills.

ettore bugatti - 6/11/15 at 11:11 PM

Interesting thread on Lotuselan.net

http://www.lotuselan.net/forums/lotus-chassis-f36/new-chassis-t26728.html