Is my ebay chassis square enough?

[beardydave]

In February I bought a chassis off eBay described as being professionally welded and painted. Mostly. Paid just over £100.

Since then it's sat out side my garage waiting for my former housemate (who moved out in October last year) to clear the last of his stuff and restoration project out of my garage, and last month the chassis was moved into the garage and sat on axle stands.

Last night I finally got round to taking a tap measure to it in anger, and I found things less than completely perfect. I'm an engineer by trade, and well aware of things call manufacturing tolerances, particularly in welded frames, but I've got no experience of chassis, so I've put the measurements I took below for your advice as to whether I've bought a chassis or a piece of scrap metal.

Desired figures are given in brackets after measured figures. These were taken with a tape measure so have a probably measuring tolerance of +-2mm

p34 - bottom rails

• BR5/BR6 vary from 1117 to 1118 to 1117 apart across their length (1118)
• BR5 & BR6 = 811 (813)
• BR10 and BR12 vary from 1383 to 1382 apart (1385)
• Width of chassis @ BR10 = 919 (924)
• BR7 and BR12 vary from 2091 to 2090 apart (2095)
• BR8 and BR9 vary from 473 to 475 apart (478)
• FF1 and BR12 are 2355 apart (2360)

p35 - front frame

• FF1 = 395 (392)
• FF4 = 628 (630)
• Height of front frame = 353 (355)

The rest of the chassis measured up ok where I could measure it, although the transmission tunnel tapers out from about halfway along it's length (going back to front) where the book shows it as parallel until the tapering out for the gearbox/foot wells.

Suspension points

Front suspension p47

• Upper wishbone brackets = 667 & 668 apart (670)
• Lower wishbone brackets = 490 & 489 apart (494)
• Damper brackets = 625 apart (630)
  
• Upper lengths apart = 192 (194)
• Lower lengths apart = 310 & 308 (310)
  
  Hard to measure but the damper brackets appeared to be positioned the right distance back from the front upper brackets.

Rear suspension p49

• Upper wishbone brackets = 604 apart (602)
• Lower wishbone brackets couldn't measure but the rails they were attached to were correct, and the brackets all looked laser cut and were identical, so I assume they were correct to each other at least.
  
• Upper lengths apart = 221 & 220 (222)
• Lower lengths apart = 314 & 316 (318)
  
  Still need to find a way to measure the top damper brackets.

I've not checked the actual squareness of the rails to one another, that's my job for tonight.


As to the professional welding: At least 3 different welders have waved a torch over it at different times. The person I bought it off welded some of the TT panels on around the drivers foot well, his style has lots of splatter and lots of blobby spots, no continuous runs. Another style looks ok but is rather blobbly too, mostly on the transmission tunnel. The other, presumably the oldest as they make up the bulk of the welds on the chassis that isn't transmission tunnel is really good MIG work.

The worst part of it though is that I'm not confident that I could do much better than welder no. 2 if I were to start again from scratch!

I do need to do some modification to the chassis, as the diff I've got has an offset input and needs different mountings to the Sierra diff the chassis has been built for.

I'll post up the squarness tomorrow, but first thoughts on the dimensions, particularly the suspension?

[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.