Chassis descision

[greg40green]

It always makes me smile when I see this topic come up again and again .
Several people I know including myself who have bought un-galvanised Lotus / LR chassis over the years have been appalled by how distorted they are are from new.
I personally went to collect my new LR un-galvanised chassis back in the 90's from the old Christopher Neil's dealership and witnessed an employer beating a chassis with a weighted hide mallet via the rear turrets.
When I approached the counter I informed that I did not want the chassis that was being knocked about in the car park.
I've since been advised that all chassis at that time 'required straightening' before sale , some being beyond adjustment with a hide mallet ie scrap.
Yes, hot dipping / galvanising may - may not cause some distortion.
Speaking from personal experience ,it should be considered that production of some of the LR chassis depending on source was appalling.
My advice is that when checking the dimensions of a new LR chassis , do not just depend on measuring from corner to corner , turn the chassis on its side and measure from top rear corner to top front corner , then on the same side of the chassis measure bottom rear corner to bottom front corner , turn the chassis over and do the same on the other side of the chassis .
Be prepared to get a shock , no matter how much beating with a hide mallet your able to do , it will not rectify a poor manufactured chassis.
If Jono's galvanised chassis is dimensionally correct, as I would expect parts from Jono to be , it would be a really good buy , much better than a powder coated or painted one .

Imho best is new Lotus galvanised Chassis.
As I understand it new chassis are no longer supplied galvanised, or is it even recommended now, due to the risk of warping/twisting in the galvanising process.

Alan

[ericbushby]

An `old school` blacksmith made me some new garden gates but when I asked for them to be galvanised he said there would be an extra £50 charge for straightening afterwards. He explained that the local galvanising company deliberately drop the product onto a grill to shake surplus zinc back into the tank. At the working temperature there would be some stress relieving as well.
My chassis is galvanised and I am very glad that it is.
Eric in Burnley
1967 S3SE DHC

[Donels]

IMHO the only difference between galvanised and ungalvanised chassis is time. They both have inbuilt manufacturing stresses, but the galvanising process releases the stresses, hence the distortion. In non galvanised chassis the stresses are gradually released over time with normal weather induced heating and cooling so will still distort.
Castings and forging where manufacturing accuracy is required are left outside for a couple of years for this weather induced stress relieving to occur before they are machined.

[alan.barker]

When i was in the Aero Space Industry they were stress relieved. Then rough machined and second stress relieved. After final machining. This was with different Alluminium alloys.
Alloy

[tonyabacus]

Alan
Remember that shims will only align the body on the chassis, they will not take out any inherent twist that already exists.

Certainly a dimensional check is worth doing, but how you measure any twist is likely to be more complicated as you need a true flat surface for that. Typically you may need to either find someone that has a laser jig or has a large flat surface table and surface blocks.

The chassis is mounted on the surface table with the blocks placed at strategic points front and rear and towards the outer limits of the chassis. This will allow you to take measurements not only at the corners of the chassis but also along its length to show where variations occur. Depending on how much variation is found will determine whether or not it is worth trying to remove any twist. Providing there is only a small variation, leave it alone and bear in mind, that you can to some degree dial out and compensate by corner weighting the car once it is all back together, as this will have more effect on handling and feel of balance if done correctly.

Trying to find a large enough perfectly flat place for measuring will likely confine you to largish machine shops, so a friendly body shop with a laser jig make be an easier route
Tony

[alan.barker]

Hi Tony,
Yes your're right spot on.
For me the Shims are to not stress the Body and induce Cracks + prevent contact with Cam Cover. I'm sure the Bodies are a bit assymetric too.
Like they say you can't make a Silk Purse from a Sow's Ear.
Always something to do or chat about with Lotus.
Alan

[Andy8421]

IMHO the only difference between galvanised and ungalvanised chassis is time. They both have inbuilt manufacturing stresses, but the galvanising process releases the stresses, hence the distortion. In non galvanised chassis the stresses are gradually released over time with normal weather induced heating and cooling so will still distort.
Castings and forging where manufacturing accuracy is required are left outside for a couple of years for this weather induced stress relieving to occur before they are machined.

Having had a further look at this, the main problem appears to be the temperature of the zinc bath during dipping. Raising the temperature of the steel to 450C significantly reduces the ability of the steel to resist the internal stresses that were introduced during the manufacturing process (bending, forming, welding). When heated, the stresses cause plastic deformation in the weakened steel which leads to distortion. The attachment below explains this better than I can.
It is not clear to me that this is a time related effect, and that an un-dipped chassis would suffer the same problems over time.

https://galvatech.co.za/avoiding-distortion/

[alan.barker]

So should the non galvanised Chassis have been stress relieved by heating. Which was never done for various reasons.
E.g. costs or risk of warping and becoming scrap ( chunky wouldn't like that or gartrak)
Alan

[JonB]

Seems to me you need to straighten any folded sheet steel chassis, whatever its source. So may as well be galvanised for rust protection.

Which rather begs the question - how did Lotus do it? If their new chassis (plural) were generally bent, how come everyone raved about the handling? A twisted chassis would show up pretty quickly if my experience with these cars is anything to go by. See old thread "Oversteer on corners" if you're really interested - viewtopic.php?f=59&t=41214 - but long story short, it was caused by 1mm of play in an anti roll bar drop link bush. So I theorise that if 1mm of play at that point could have such a profound effect on steering, think what similar amounts, or more, of chassis distortion could do.

Now as to the pptom's original question, I wouldn't use either chassis. But then, I do have the luxury of having a NOS spare to hand. My (original) chassis had some rust in the front turrets which repaired well, so I am using it, though I do not know how straight it is (I measured corner to corner and it looks OK, but you can't be sure unless you have access to a chassis jig).

Regarding the markings on chassis 2, do these match the unit number on your car in any way?

[pptom]

Markings don't match anything I have, it's basically L321. Located just opposite and in front of the oil pump

[alan.barker]

Good question ' how did Lotus do it' flog Cars with twisted Chassis and Doors that Kicked Out at the bottom corners.
Mmmmm i'll need to think about this !!!!!
A bit like a Magician trick.
Thanks Jonb for the enigma
Alan

[Donels]

My replacement chassis was numbered LR1141, LR being Lotus Replacement. So yours could be Lotus produced original chassis 321. I'm sure Tim, trw99 will know.

[alan.barker]

Not Lotus produced but Gartrac
Alan

[greg40green]

Hello Jon ,PM sent re your galvanised chassis .

Perhaps I could interest you in a genuine Lotus galvanised chassis, unused.
PM me… thanks!