Is my ebay chassis square enough?

[jason 82]

Don't scrap the chassis. I would get my book out and go through the different rails, checking its dimensions, and correct them as I went along. 25mm box section is really cheap, it's nothing that can't be repaired with a little sun and a few cold beers ! If you leave these problems, you will have trouble with suspension alignment & cosmetically, you may struggle to get off the shelf bodywork to fit. On the weld side of things, if the builder has struggled to follow a build spec, I would have massive concerns about their welds. Every welder I have ever known knows how to measure. I would test the welds, and rectify any rubbish ones as I went along, your life depends on it !

[beardydave]

That was my thoughts regarding the welds, anything I'm not happy with will be re-done but some of the rails that are wrong are the main lower rails BR1-B12.

To change those I've got to grind away most of the chassis, and without a build table there's no guarantee it will be any better when I've finished.

Apart from the chassis overall being 5mm too short, which in no way can be put down to tape user measuring error as I double and triple checked those measurements, the only bits that concern me are the suspension points.

They are only a few mm out. Will that make much difference that can't be corrected in the adjustment on the wishbones?

[Stot]

Mine is 5mm shorter overall and one corner is about 5mm higher than the other 3 due to welding distortion.

I done lots of research on how much was too much. I came to the conclusion that overall a few mm here and there wasnt a problem as long as you jig the front suspension mounts. If you look at it and its visibly out of line (a banana) then worry about it.

For me the 5mm length means a shorter propshaft in reality and the corners will be sorted by suspension height adjustments.

In practice once built and im in it I recon the ride heights and levels will change by more MM depending on what meal Ive had, wether Ive been to the loo and how much fuel is in the tank anyway.

Cheers
Stot

[jps]

Dave, I've wondered the same as I bought a second hand chassis too. mine was already a rolling chassis though, so at least I have the reassurance that the wish bones are in an appropriate place for them to function.

I started the ' car building' process thinking it'd all be about fine tolerances and components that were aligned to thousands of a millimetre....

then: a) someone pointed out to me how much a tyre deformed during cornering, etc.
and b) I read a story somewhere of a chap who measured his production salon car ( model I think) and found it was over 10mm longer one side than the other...!

getting body panels etc to fit shouldn't be add problem, grp is pliable.

if a jig is used for wishbones then they'll be aligned correctly to function.

in terms of it looking like a banana, if it looks ok to the eye, none will know if you've had to do some correction in the set up...

[beardydave]

Last night I borrowed some measuring equipment from work, specifically a digital protractor, venire protractor and a laser tape measure.

And with the able (if not quite willing ) assistance of my girlfriend, re-measured everything and checked as many of the angles as possible, the zero button on the digital protractor helping a lot as it removes the slope of the chassis due to axles stands of different heights on a slightly sloping garage floor.


Most of my tape measurements were accurate to 1mm, and pretty much every rail is at the angle it's supposed to be, with the exception of the sides of the cockpit where one side is 3° too steep. I think I can live with that though.

Standard bodywork isn't an option for me anyway, as i'm fitting a Saab turbo engine mated to a BMW gearbox, and possibly fitting a bigger fuel tank. The only standard bits that would have fitted were the side panels.

I will now be checking the TT against the modified chassis dimensions for the MT75 gearbox, as I suspect the chassis was modified by the second owner to make a wider TT. All of my drawings for fitting the E36 BMW gearbox in were based on the standard chassis, and it was looking tight, so this might actually help me out.