MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Front cross member bolt centres

I am currently helping a friend with his total restoration of an early Mk1 B roadster. Following acid dipping the original body was deemed as beyond repair due to chronic tin worm so an ex California shell was purchased. Fitting out is now underway but a problem with fitting the original front suspension cross member has reared its head. Following a number of failed attempts to locate the four fixing bolts through the chassis rails, a measuring exercise revealed that when measuring across the width of the engine bay there is a discrepancy of approximately 8mm between the centres of the holes in the cross member and those in the chassis rails. The approximate measurements (using a tape only) are 480mm ctrs between the chassis rails and 472mm ctrs between the cross member holes. This differential is enough to cause the bolts to jam in the chassis rail tube guides. The first thought was body distortion through impact damage but although difficult to visibly check, there are no typical signs. Has anyone come across this before? Is there a hole centre difference between Mk1, Mk2 or rubber bumper? Any information would be gratefully received.
Thanks
Chris
Chris Woodfield

As far as I am aware there are no dimensional variations from model to model, apart from the BMC BL discrepancies that is!!!! Is your 480mm measured from below? If you measured across the top of the rail you may find underneath is different, Measure and compare both, the rail could be twisted. But don't understand why you are having problems fitting the bolts. They go into the rails first and are torqued up, the cross member is then lifted into place. There is compliance in the rubber/poly pads but probably not that much.
Allan Reeling

Allan
I take your point about BL discrepancies but even they surely could not be that far out. I certainly have never heard of model differences either, so clearly there is something amiss. That's a good point re measuring both ends of the rail tube, although the rail sides do look to be perpendicular. I don't think the raised locating portion of poly pads is causing the problem even though they are a slightly larger diameter than the rubber originals. Like most B problems I'm sure there's a simple explanation. Definitely more investigation needed.
Thanks for your comments
Chris
Chris Woodfield

The spec I have is
471mm c-c for the front holes
512mm for the rears
both plus or minus 1mm
William Revit

William
Your dimensions are very interesting. Your 471mm is pretty well the same as my cross member hole centres. This does suggest that my problem is with the side rail hole centres. Many thanks for the information.
Chris
Chris Woodfield

Chris

I just measured my unmolested original 1964 MGB cross member which is off my car and the measurements are the same as Willy's. Maybe the rear if 515mm but close enough.
I have a rubber nose cross member fitted to my car because of the V8 conversion and that fitted perfectly at the time; so there is no difference.
Ian Buckley

Hi Ian
I haven't heard from you for a long while. I agree with the comments to date and my understanding is that there should be no difference across the models in these hole centre dimensions. It really is confusing because nowhere on the shell are there signs of anything having been 'massaged' back into shape after for example a shunt. Having said all that, a discrepancy of circa 9mm is sizable and only more dimension and alignment checking, starting with Allan's suggestion of measuring between the underside of the side frame bolt tubes, will determine the underlying cause.
Good to hear from you Ian.
Chris
Chris Woodfield

FWIW the Leyland Workshop Manual quotes 473.07 +- .79mm for the fronts and 512.14 +- .79mm for the rears.
Paul Hunt

Thanks for the info Paul.
Chris
Chris Woodfield

Chris,

I don't think the numbers work out to support this, but since the front and rear holes are different C to C, is it possible that you have it reversed right to left?

Charley
C R Huff

Ian
That's an interesting move fitting the later x member for your v8 conversion I have a friend that went the other way and fitted an early one in his factory v8 to lower the ride height
willy
William Revit

Charley
A good thought but I have only measured (across the width of the chassis)the centres of the front holes at this stage. Everyone confirms this dimension should be circa 471 to 473mm whereas my measurement is 480mm. I will measure the rear holes during further investigation.
Chris
Chris Woodfield

Chris, good to hear from you and talk on this BBS. I hope you are keeping your gear lever polished ! In a former life it was used to Australian sunshine.

Willy using the later Xmember and rack and pinion assembly lowers the angle of the pinion so it is clear of the rear right side exhaust port on the Rover V8. The pinion is longer so the UJ is a little higher and out of the way.

The downside is that I need to use shorter springs to retain the original ride height and keep the wishbone arms/steering arms parallel. Some people don't think this is a problem but I think the shorter springs have disadvantages. I am often tempted to refit my original Xmember and fabricate rack mounts to accommodate the later steering assembly.
Ian Buckley

"is it possible that you have it reversed right to left"

Do you mean facing the wrong way? Given the 30mm difference when the discrepancy is only 8mm I don't see how that could be possible, especially given the rack brackets would be facing the wrong way. I can't think of any other way that one might attempt to install it.
Paul Hunt

Chris,

It sound's as if the shell's had a minor (?) shunt at some time. If you could get it to a body shop they may be able to squeeze the legs together a little with their hydraulic kit. Do the bolts at the back line up? If so, you could bolt the crossmember in on the back bolts and see if the discrepancy is symmetrical. If so, could you file out 4mm each side of the crossmember front holes. Or is that too much of a bodge? Or will three bolts go in - 8mm on one side might be a little too much to modify.

It might be worth running a tape measure over the rest of the shell.

Peter

P A Allen

Peter
I must confess that although evidence of shell distortion is not immediately apparent, misalignment caused by a shunt is a real contender. Fortunately the shell is actually in a resto shop environment and further investigations will begin later this week.
Chris
Chris Woodfield

"they may be able to squeeze the legs together a little"

You really need to find out if only one leg is bent, and straighten that. With the way that metal work-hardens, by tensioning one against the other you are more likely to bend the 'good' one in the same direction as the 'bad', which will misalign the cross-member. Easier said than done though, with 'only' 7mm of error. You probably need to pull a line between each of the front holes and the rear spring hangers, both in line and diagonally. No less than 18 chassis alignment measurements in the manual.

You've not mentioned the spacing of the rear holes for the crossmember, that would be interesting.
Paul Hunt

Paul
I agree with everything you've pointed out. More measuring later this week.
Chris
Chris Woodfield

Although this link gives the alignment for GHN5 & GHD5 models it is the same as what my early Bently manual, pre RB cars shows and what others have already provided with the exception of the =/- amount. I would try lining up just one bolt and then clamping it lightly in place and then see if you can align one of the holes on the opposite side.
http://www.mgexp.com/phorum/file.php?1,file=142761,filename=body_alignment.pdf
Ben Colpitts

The mystery has finally been solved. After much detective work we discovered that the original car had been damaged at some time in its life, a fact that was not known about by my friend, the owner. It appears that the damage must have been extensive because the reason the original cross member would not fit into the replacement shell was because the former had been modified (butchered) and re-welded to fit a presumably badly repaired and misaligned body. Only very close scrutiny revealed that one side of the cross member had received some serious and disguised attention, the result being that when measured from the centre of the member to the king pins, one side was shorter than the other! Remarkably, my friend had never detected anything amiss in several years of driving the car. All along we had suspected the new shell as being the culprit when in fact it was the original shell (already scrapped) that was at fault. Only when a replacement cross member was offered up and it fitted perfectly did we realise where the problem lay. Happy to have found the problem? Yes.. but the realisation that there are people out there that are so unscrupulous as to be prepared to return a vehicle to the road in such a condition, is a very sobering thought. As a foot note..the butchered cross member followed the original shell to the scrap yard and the rest of the refurb is continuing to plan.
Thanks everyone for your contributions.
Chris
Chris Woodfield

congrats chris - nice find
your measurements in the original post made it look like a bodyshell problem but as you say they were approx. measurements with a tape
anyway it's good you got it sorted out properly

cheers willy
William Revit

Chris,
If you need a good RB cross member I have one.
Allan
Allan Reeling

Sorry Chris just realised yours is a Mk 1
Al
Allan Reeling

Well done, worth persevering to find the root cause.
Paul Hunt

This thread was discussed between 04/09/2014 and 13/10/2014

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now