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MG Midget and Sprite Technical - Front chassis rails angle

Hi everyone,

Can anyone quickly tell me what angle the front chassis rails should rake upwards at. I have a figure of 2.5 degrees stuck in my head for some reason?!? But I have no idea where this has come from.

I could be gearing up for a confession of a monumental disaster here so stay tuned... :-)

Malcolm
M Le Chevalier

No angle i just know not to touch them!
Or use heritage pieces to fix it so the angle stays the same.

Yeah I am just here to see the disater unfold (we all had one at some moment)
Onno Könemann

I took this picture at BMH on a factory tour

I didn't think to ASK about the angle and given that these original factory jigs were older than some of the factory staff suspect they mightn't have known anyway

I printed this version off the last time we had this discussion (It was with Guy if I recall correctly)

I measured with a ruler and protractor as best I could and the visible angle of the "kick-up" is 3˝°

This is of course only my observation

and the block on the next jig that sets the height at the front is one inch tall

I dont think you will be far off if you work to this angle

HTH


Bill 1

Malcolm,
If you think about the purpose of the upsweep, and the geometry of it, then the angle should be the same as the castor angle. Which is listed as 3 degrees. That is the angle I used on mine.

Guy

3 degrees is what is listed in a reprint of a road test report from "The Motor", December 1962
Guy

ok... next question, this should be an even easier one (and you might be able to see where this is going...) the front 'assembly' (valance/radiator duct/bonnet catch bit) should bolt to the front chassis rail with a couple of bolts down into the rail and three bolts into the upright 'prongs' that come up from the rail a few inches back from the front? yes?

And the valcance should hide the rails when looking from the front?

(this bit wasn't attached when I bought the car... hence stupid question, just making absoloutly sure!)

Malcolm
M Le Chevalier

4 bolts down and several to the side in the prongs (keep them loose until the full front is fitted)
you can just see the rails from the front (looking from a low angle) though mine can't realy be seen since they are painted black.
Onno Könemann

oh............................
M Le Chevalier

In agreement with all that's been said, I measured mine with a digital protractor which was 'zerod' on the level part of the chassis rail and then measured the kick up both sides relative to the level part:

Drivers (RH) side 3.5 Deg
Passenger (LH) side 3.0 Deg

I assume this is either manufacturing tolerance or 30+ years of possible mishaps to tweak things

Cheers

Spencer
S Deakin

OK.... so I think I can be pretty sure of what has happened and here comes the confession...

When I bought the car the front assembly and wings weren't attached and the car was pretty rusty but I didn't much care as I was looking for a resto project anyway.

I got all the bits transported to my garage and began pulling the car apart and chopping out the rust. A few weeks ago I got some new panels for replacing (passenger side UK) footwell top and front, triangular chassis structure and front wheel arch. When putting things in place it never all seemed to line up properly...

Last night I thought it might help if I put the front assembly on to help line things up... resting it on the bumper mount on the driver side the holes didnt line up and it sat apart from the chassis rails by about 40 mm. Uh oh....

so... if the upward sweep of the rails is approx 3.5 degrees over the 27 inch length of the front rails forward of the bulkhead the rails should rise approx. 40 mm (sorry for mixing units!). Hey presto... same as the gap... some utter plank has straightened out the chassis rails.

Oh big hairy bottoms! I have bought a pile of...

I would like to swear a lot here...

Malcolm

M Le Chevalier

http://www.mgocspares.co.uk/acatalog/MGOC_SPARES_PANELS_OUTER___midget__141.html

If I understand correctley nr 24 would fix it......

Bugger but now you know why it is easyerto buy resto's as roling fitted projects.
With boxes you can encounter al sorts trouble you otherwise would avoid.

But that is no help now sorry.

Look from the bright side you found out before it was all painted!
Onno Könemann

hmmm... yes, thats what I was afraid of... thats 1.5 times the cost of the car in the first place! ha ha.

Malcolm
M Le Chevalier

The change in angle isn't at the bulkhead. It is immediately behind the rear fulcrum bracket
Guy

hmmm... OK guy, maybe I have jumped to the wrong conclusion.

I think my plan of action will be to get the rear axle off and get it sitting flat on its floor, then I can better look at things without the wonkyness of the way it is currently supported confusing things.

Urgh...
M Le Chevalier

Don't give up yet, Malcolm. I have seen tales on here of people who have thrown themselves mightily into the project of straightening those rails and utterly failed, so it isn't real likely that your DPO succeeded at it.
David "optimists are merely uninformed pessimists" Lieb
David Lieb

look at the picture

look at the assembly jig (for tis what this is)

you can see where the upkick begins, right at the back of the front crossmember

Lots of people have rebuilt this section with little or no angst

Go on, you know you can

Snip off

Glue back on 40mm higher at the front

you will be done by Friday, off you go

and cheer up

many/most of us have been where you are

(my oft' told here, true confession, when I began renovating my car I discovered that the front of the chassis was "bent up" by the crossmember.
Thinking this indicated a previous crash many years before I bolted the car to the concrete floor of my garage with Rawlbolts and bounced up and down inside the boot hoping to rectify the "fault")

Lucky me I didn't manage to bend it back down, I saw another Midget chassis first and realised, they am all loike that

Most of these blokes and blokesses have heard this one before so I am only moderately embarrassed these days by admitting it
Bill 1

ha ha ha, I was reading that story in the archive last night!

Ner, I'm not giving up yet, just was hoping to start making some progress forwards (welding bits on) rather than having to hack and grind and bash more bits off/straight.

Perhaps its the drivers wheel arch/bumper support and associated periphary that has been bodged on too high, that might be less stressful as thats all rusted to hell anyway and needs fixing up!

Anyway... bed time for me!

Malcolm

M Le Chevalier

I measured a new heritage subframe we got to fit to ours after smacking a gate and a couple of fenceposts and a kerb during a few years of hillclimbing. The kick-up was exactly 1", measured at the front of the rail. This has a certain logic to it I would think:
"We need a bit of castor, so we can do it simply via the angle of the chassis"
"How much?"
"About an inch should do it"
Paul Walbran

surely everyone who has seen that bit has looked at it and gone 'ooo err shouldn't that be straight?' I know I have.

Mine's even more bent up than that, but only in front of the front wishbone mounting (I can see the crease :S ), so the geometry is OK (I checked it) I decided not to try and straighten the very front, and somewhere in the archives will be me going ooh it's bent and everyone else going nooooooooooo don't straighten it!

mine just makes the valance harder to fit :(
and the ARB wears its bushes out fast.

I think Paul has it right as to how they did it :)
Rob Armstrong

That's probably how it happened. Of course for anti-dive geometry, you'd want the bend to be in the opposite direction...

If anyone has straightened the chassis out... the easiest fix might be to cut off one of the wishbone mounts - say front one - and replace on chassis a bit higher up to compensate.

Or maybe Peter May sells offset lower trunion bushes for this purpose? ;)

A
Anthony Cutler

Ant,

<<cut off one of the wishbone mounts - say front one - and replace on chassis a bit higher up to compensate>>

that wouldn't work. The purpose of the upsweep also cants the whole turret and shock mounting over by the same 3 degrees.

I believe that the change in angle is immediately behind the rear inner fulcrum mount - not as far back as the bulkhead. I had need to inspect mine very closely when fabricating and replacing one of the chassis rails.




Guy

I have taken some pictures to add to the story, first picture you can see the front bit lines up with the side wheel arch panel but the rails poke out the bottom.

Second picture is a disaster! It looks like the rails are just bent all over the place. They appear to slope down from the bulkhead and then up again at the correct place. A complete mess.

I might just saw the whole front end off, fix the rest of the car then put it back on at the end!

Or I have a couple of floor pans. Throw this shell in the bin and build up a new shell from the floor upwards!

It confirms my suspicion that I think the car has had a big shunt and some very bad repairs done on it.

You should always take someone knowledgeable with you when you go to view a car, and never buy the first one you see! oops...

Malcolm
Off to B&Q to buy a really good hacksaw...


M Le Chevalier

Hmm, see what you mean.
The ends at the front of the rails usually show about 1/2" below the bottom of the front valance - yours look like showing 1 1/2". Have the chassis leg extensions at the front been replaced at some stage? Repair pieces weld on immediately in front of the front cross member and it is easy for them to have been put on level instead of continuing the upward slope of the chassis.

The main chassis rail should be dead flat from where your axle stand is and continuing right back under the floor pan. Check with a straight edge or taught string line. On yours it looks like the flanged edge is buckled which accentuates the bend. Don't worry about that, it would easily dress straight with a few hammer taps - it is the main surface of the box section that matters.
The upwards bend going forwards from the axle stand looks about right.

I have seen worse! The chassis rails are prone to rusting where the triangular box section formed from the bulkhead and the angled toe plate (behind the pedals) meets the vertical outer side of the chassis rail. Weakness here could cause it to buckle if it was jacked up at that point.

Guy
Guy

any idea how the chassis would respond to me turning it upside down to have a better look at the underneath! :-D

Can't be that heavy just to pick it up and 'throw' it over ha ha!

Malcolm
M Le Chevalier

If you have most of the running gear off, then one person can tip it up on its side quite easily. Tip it up onto an old mattress, carpet or a couple of tyres to stop it damaging the body panels.

If you leave it up on its side do prop it (or tie it up to your garage roof) - It may not be that heavy but you do not want it dropping on your head!
Guy

there is only the back axle left on at the mo.

off to the garage to drop a car on my head....

Malcolm
M Le Chevalier

Hi Guy

You're right!

It would need a tweak on the damper arm, too!

A
Anthony Cutler

This thread was discussed between 22/03/2011 and 23/03/2011

MG Midget and Sprite Technical index

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