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MG Midget and Sprite Technical - IRS Hub options to keep Midget PCD

Hi guys,


Here's a bit of a doosie for some of you engineering types to wrap your brains around and have a creative think about, at least I hope some of you may enjoy the challenge!

So first a bit of background... I have owned my car for nearly 10 years and in that time it has been a constant source of mechanical engineering pleasure as well as driving pleasure. The basic evolution is from standard 65bhp 1500, to tuned 105bhp 1500, to standard 160bhp C20XE, to turbocharged 197bhp C20XE. Obviously over time I have beefed up parts of the car to handle the increases in power but now I am getting a bit beyond a few bits of the current car.

These are mainly the standard 1500 diff, and the rebuilt type 9 gearbox. Neither of which was designed for the torque generated by a turbo engine, currently at 166lb/ft.

So the solution... why a space frame chassis of course! Am I mad?!? Hopefully not, it doesn't sound so stupid when you take into consideration a couple of things.

The car has been so cut and welded over the years that there is little strength left in it but a lot of tin worm.
The current drive train is so modified it is already compromised in the current shell.
Gives me the opportunity to have IRS. Gives me the opportunity to have a bigger, stronger gearbox, plus I already have a fibreglass front and rear so that takes care of a lot of the bodywork.

So that's the route I'm going, I have attached an image of a basic first draft of how the space frame is going to look (with a lot more triangulation still required to be added!) for your interest.

The real issue is how to keep the midget PCD at the rear with an IRS setup?

I am planning to use a BMW diff as it fulfils a lot of criteria, strong, easily available in different ratios, available with LSD. I can have the drive shafts modified to keep the correct track, and will custom make my own adjustable wishbone setup to deal with the geometry(ala Locost suspension setup). What I need though, is a rear hub/bearing with a handbrake option and the midget PCD which can fit a BMW driveshaft!

Now I appreciate that this won't be an off the shelf part, and I am happy to manufacture/modify what I need, but I just wondered if anyone had any clever solutions they could think of, or previous experiences which could help.

It always amazes me the communal knowledge of this forum and it is always good to hear others views, any and all contributions are appreciated.

Regards
David


D Prince

And from the side to make more sense...


D Prince

that sounds cool. and is cool. Though why keep Midget PCD? There are other wheels around (e.g. Ford PCD) which would give more options for a rear setup.

It'd be cool to see a build thread - either on here on or www.kmidget.com - sounds like a great car. there are a couple of guys over there building rear disc setups and some independent rears too, which might help.

What are you doing/have you got for brakes? JLH does a (big) front brake kit with Ford (or midget) PCD which is very good.
Rob Armstrong

Hi Rob,

Thanks, I thought so too!

I wanted to keep the standard midget pcd to try to keep the overall look of the car right with the size of wheels, and styles available for Midgets.

Another reason is that I have 2 sets of Midget wheels, one with anthracite minilites & road tyres, and a second set with AO48's.

Finally I do have the JLH big brake kit already fitted with the Midget PCD... which is excellent by the way... but as it was a reasonable cost not that long ago, I am reluctant to lose it immediately.

I am planning to create a front double wishbone setup which incorporates the original Midget front kingpin/spindle, so I guess if all else fails I can speak to Jonothan and get the Ford studded alloy hub to replace it. That will be my backup plan... Ford Sierra rear hub setup

David

D Prince

Can't you redrill the ford rear setup to match the midget pdc?

Nice plan btw
Onno K

David, you might be interested in our new kit. And we can sell Ford PCD hubs to fit your existing JLH kit


J L HEAP

I'd have thought that was an option - not sure how much meat there is on a rear hub from a sierra. Simon on the K midget site would maybe know - he's fitting de dion to his midget.

the estimable mr heap is playing with a front suspension replacement, looks lovely but is many beer tokens.

I looked at some options for front susp when I built my strengthening top link, and couldn't get anything that retained the stub axle while satisfactorily fixing the bottom link. Have you looked into Spitfire/Herald front suspension? Favoured by kit car guys ad has a proper wishbone arrangement.

With the space frame are you thinking of building it round a shell or 'with' a shell? I saw a race midget once with a space frame rear end, I'll see if I can find a pic.
Rob Armstrong

Dave , we are soon releasing an alloy version of the original upright but with ball jointed trunnions, (the top one vernier adjusted for camber change / set up) It has a bolt in stub axle too to take either the 1 or 2mm radius bearings. Saves about 1.5 kilos a side in weight too


J L HEAP

Mine lacked the quality and engineering prowess, but it worked. If I still had the car I would have changed the rose joints for something safer.


r thomas

I'm niot sure how Stuart set up his hubs

Stu built his spaceframe to run his Rover V8 through a Cosworth 4WD set up




bill l

another


bill l

Ithe frwme looks great, but also heavy

Should be a fun build

Prop
Prop and the Blackhole Midget

David
Good looking frame
A fair bit of metal (too much) around the dash area, but I guess it's only early planing days
On the bolt pattern for your rear wheels----
If the BMW hubs are the small 100x4 bolt pattern you would get away with wobble nuts for 4"x4 --101.2mm wheels
That gives only 0.6mm difference on each stud which the nuts will easily cope with
The wheels need to be a neat fit on the hub to centre them if you went this way
Lots of VW guys use them because of their weird bolt pattern

willy

William Revit

Forgot the main bit
cheers

http://www.guerillaracing.com/wobble-nuts-5x112-wheels-on-5x114-3-car-m12x1-25/
William Revit

Thanks guys,

I like the look of the new front suspension setup Jonathon, but the front I am happy to build around what I have already that shouldn't be a problem.

The wobble nuts are an interesting option Willy, thanks for the heads up with those, I shall have a look at those.

The rear setup I have envisioned is something like that shown in your images Bill, I'm guessing that will be ford all round though on that particular example.

The space frame designs attached are definitely a first draft, but weight is not my primary concern, obviously I want to keep it low but the reasons I am doing this space frame chassis is for strength, longevity and fun!! There will be a lot of redesigning yet I am sure but the reason I need to sort the rear setup is that every other part of the car depends on it's location and track. As all the suspension mounts are going to come off heavier duty chassis rails I need to be sure of their location before I begin to position them relative to the body.

D Prince

I probably should have explained how the wobblenuts work
The tapered seat part is seperate to the main body of the nut and can float sideways up to about one mm it has a flat top and contacts a flat surface on the nut
A couple of mates run them on their VW club cars and have never had a problem at all with them
willy
William Revit

Willy

Thanks for the input on wobble nuts, I was not aware of anything like that before

If you have round wheel arches, you might be able to use a wheel spacer adapter for the correct PCD

Prop
Prop and the Blackhole Midget

David, It looks like a really interesting project. The Spridget main tub is pretty stiff when in reasonable condition and light too. Your new frame looks massively heavy unless you're going to use very thin-walled tubes. I'd be tempted to do a really good repair and make the tub as perfect as possible with a few added gussets and then make custom subframes for the front and rear. As for the Independent rear suspension, with a new subframe you could go for a transaxle. But as there are a lot of old 3-series BMW in the scrap yards, I'd be tempted to use their diffs and shafts - quality parts and cheap second hand.
Nick Nakorn

If going to big power and torque, wheels and tyres plus better brakes I'd be tempted to go for a bigger stud on a 4" PCD or better still a bigger PCD and stud. Our modified cars all go to Ford 108pcd and 12 mm studs. I would not use adapters with the power figures you are thinking of.
J L HEAP

Hi Nick - Your're right about the Spridget tub being relatively stiff in good condition but unfortunately mine is not, It has been cut and compromised in so many places now that it really isn't worth the repair.

The BMW diff is a route I wanted to go because of the range of varying ratios available, the BMW hubs unfortunately aren't easily useable as the carriers are built into a much larger part, which isn't easily adaptable.

I already have larger studs in the hubs which are currently in the car after this...

https://www.youtube.com/watch?v=rgWyHx23vBc

But you are probably right I will almost certainly go up to the 108 x 4, just to make life easier if nothing else!
D Prince

Hi

Following Rob's suggestion of Triumph Herald or Vitesse uprights with fabricated wishbones - this was used on many racing cars, some kit cars and a Lotus/Caterham Sevens. Note that you can get alloy front hubs to fit these uprights to match Ford and other rear axle hubs that have different PCDs to the Herald/Vitesse (see:
https://www.merlinmotorsport.co.uk/s/suspension-steering/alloy-hubs-and-bearings/alloy-hubs)

Cheers
Mike
M Wood

Hi JL, are those front suspension kits for Midgets or Minors??, can't seem to find any listing in the Midget section of your web site. Very interesting.
Cheers
Rod

R W Bowers

Hi Rod, the kit shown above is for Midgets, A30,35,40, and some Westfields. Nothing on the site yet as this kit is about to have some hefty testing to prove itself in all aspects of Midget Motorsport and road going /trackday cars. I can email you more info if you are interested.
J L HEAP

How about an MG TF rear subframe? Probably needs narrowing and not sure what attachement points would need to be fabricated, but you would be well on the way. You would need a diff (BMW?) and fabricated drive shafts.

I thought of this in a thread last year when someone, jokingly, suggested putting an MG TF engine and gearbox with subframe in the back of a Midget.

If Prop is reading this, it's the 1990's MT TF not the 1950's.

Rob
Rob aka MG Moneypit

Thanks JL I'm interested please send info to
rbowers@rochdale.edu.au
cheers
Rod
R W Bowers

Have a look at this, guy building a spaceframe midget....RX7 engine/box/rear IRS

http://s33.photobucket.com/user/Nocones/media/midget/10-05-08-07.jpg.html?action=view¤t=03-08-2012-05.jpg
Andy Phillips (frankenfrog)

This thread was discussed between 05/01/2015 and 15/01/2015

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