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MG MGA - Chassis Twist

With the chassis restoration virtually complete, I've found that my chassis has a slight twist along the length. By this I mean with the chassis level at the rear body mounting plates, the front is out of level by approx 2mm across the front shock mount plates (or vise-versa).
Would this be within 1950's tolerances or should I try to correct this?
For the record the diagonally the dimensions are good.
Chris Bond

Chris, That sure is a 'slight twist'. When I rebuilt my MGA 37 years ago I 'chased' a diagonal shortfall of 1/4inch only to later find a Factory tolerance of 3/8inch.
I would say that 2mm. front to back, is within tolerance.
Good luck mate, Barry
BM Gannon

Thanks Barry. I thought so as well but just wanted the opinions of the very knowledgeable members of this forum.
Chris Bond

Chris, I agree with Barry, 2mm seems a very small twist and very difficult to correct. My frame was shorter on the right side by 3/8" between the rear axle and the front cross member due to an accident during it's previous life when it was hit hard in the front right corner which pushed the front of the frame in. It took a frame shop many hours to correct it and they could only get it to be within 1/8". So I think you should be OK.

Andy
Andy Preston

Andy, Mine has also been hit but on the left hand front, but apart from a bent chassis extension and lower wishbone pivot, the chassis diagonal measurements remained OK. Thanks for your input.
Chris Bond

I'm surprised you can measure twist to that degree of accuracy and I wouldn't worry about that amount. Don't forget that measuring diagonals will only check distortion in the horizontal plane; this type of distortion being most likely caused by a collision.
Distortion in the vertical plane can be caused for example if the frame centre section(s) have rusted badly and weakened. The frame can then sag in the centre and this won't show up on a diagonal check. I saw a roadster once where the frame sag was sufficient to cause the door tops to jam preventing them closing properly. I have known a rusted frame to be welded up without correction and with the sag 'frozen in'.
If you want to be 100% sure the frame is to spec. I would suggest you take it to Bob West for him to check it out on his frame jig. It can be done while you wait.
I have had two frames checked this way and one was out with frame sag by a couple of inches! According to BW it is the only such jig in the country.
Cheers Mike
m.j. moore

This is a question that was addressed by Eclectic. (the jigs are now in Colorado) They stated that the factory tolerance was 1/4" and that they repaired to a 1/32" tolerance.
http://www.eclecticmotorworks.com/fixtures.html
Mikes advice sounds good to me.
R J Brown

Mine also was hit on the left front. I just had the frame company throw it on the rack. They brought mine within 1/32 which was far closer than the original 1/4 inch tolerance. It now tracks wonderfully straight. So the morral to the story is you don't have to worry about a bent frame. Any frame company will make it "Better" than new for a few hundred buck.

WMR Bill

Thanks for all your comments, I've just checked this again (more accurately this time) and it is less than I originally thought - about 1mm, which must be OK. My original concern was that when it was on 4 axle stands it appeared to be far worse than this (rocking quite a lot) but on closer examination it proved to be discrepancies in the floor & stands.
Chris Bond

This thread was discussed between 03/01/2009 and 06/01/2009

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