Robin`s MX5 Morris Minor
Robin has been thinking of building another modified Morris Minor for many years. He is best known for his pick up (HERE) but this was built over 15 years ago. In the intervening year he has built many vehicles including his concours Morris Minor Van (HERE) but we have all been waiting for another modified Minor. Well he is now back in the garage building again.
He watched and helped me build my Minor and saw how much work it was and decided that he wanted a car that was simple to build with a short construction time. Also it was very important that the car drove and handled like a modern vehicle. He would not compromise on such aspects as the seating position in relation to the pedals and steering wheel. This makes a lot of sense as it is the owners main interaction with the car.
After many discussions we considered an MX5 would make a very good donor or base vehicle. The MX5 is a small car, rear wheel drive, all round independent suspension, is already a classic so a good source of spares is assured for a long time and can be picked up for a reasonable price. The car has a huge following around the world and there is a huge amount of aftermarket tuning parts such as suspension components, engine parts, super and turbo charger kits. Further research showed that the suspension subframes unbolt. Each are self contained units except for the spring upper mounts that could be bolted under another chassis.
We decided that there were several ways to build the vehicle. Inspired by the Minor based on the NSX floor pan (HERE) and the Capri based Minors from the 80`s there is the "floor pan" method. This involves cutting the top off the MX5 and welding on the Minor body shell. This means all the MX5 running gear is retained and you effectively end up with an MX5 that looks like a Minor. However the overhangs, dash position, seating positions etc must be considered.
The other way to build the car is to use the subframes under the Morris Minor body, building new chassis sections to mount the subframes if required.
Robin decided that the project was a "goer" and an MX5 purchased from a guy who deals with MX5 spares on Ebay.
INTENDED SPECIFICATION
The Base Morris Minor
Robin purchased a Morris Minor from a local enthusiast.
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The Mazda MX5
A Mazda MX5 was purchased from a dealer on Ebay. Robin negotiated the price down by only taking the
parts he would need and leaving the easily saleable items with the breakers. The car had minor corrosion.
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The Mocking Up Begins
Now Robin had the two cars he could start mocking up and deciding how to build the vehicle. The first easy
mockup was to place the Minor bonnet on the MX5 with the wheel centre lines correct. The surprise is just how small the
Minor is or how large a modern "small" car is!
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Minor Bonnet On The Mazda
This picture shows so well the relative sizes. But bear in mind the Minor wings are quite wide.
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Looking Under The Bonnet
As expected under bonnet clearance is OK. The Minor bonnet is very bulbous so there is lots of room under there.
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Space At The Side of The Bonnet
This shot shows that early in this mock up phase a "floor pan" approach will not be straight forward.
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The Ideal Seating Position In The MX5
Next Robin positioned the Minor seat in the MX5 in the position he would like it. Note: He will not be using
a Minor seat, it was what he had lying around. This mocking up is important because the idea if the "floorpan" method is
used, is to retain the bulkhead, pedals and steering column.
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The Ideal MX5 Seating Position In The Minor
Then the seating position from the MX5 was mocked up in the Minor to see where he would be
sitting......quite a long way back.
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Minor Seating Position in The MX5
This is the ideal seating position in the Minor body shell mocked up in the MX5.
It is a bit too far forward.
After a few weekends of measuring, mocking up and lots of thinking the following conclusions were drawn:
The MX5 is quite a bit wider than the Minor and to get the standard MX5 floorpan under a standard Minor would require a lot of work. I widened the body on my car and have moulds for the boot and bonnet so that would reduce the work but Robin doesn't want a wider car. The bulkhead positions don't match which would mean a lot of work if "floor panning".
An alternative to widening the body is wider wings. But Robin wants stockish looking body work.
It was decided to use the Mazda suspension subframes, narrow them to suit and mount them under a new chassis. Narrowing the rear subframe is easy and will then bolt under the chassis. At the front the MX5 subframe is quite large and bulky and narrowing would leave very little room. It was decided that new mounts would be made to take the MX5 wishbones.
A lot of work went into deciding how much to narrow the subframes. The starting point is the wheel and tyre in the arch. This must look correct and allow the wheel to go to full bump and at the front full bump and lock. So many modified cars must not be able to get full lock at full bump without the tyre catching the wing.
As Robin wants the car to ride and handle well he MUST
have lots of suspension travel, ideally as much as the original MX5. I am a believer of lots of travel with soft springs but good dampers.
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Making The Front Suspension Jig
The subframes were narrowed 5". Robin has narrowed the subframe and is making a jig that bolts onto the suspension mounts. The subframe can then be lifted out and discarded and the jig used to position the new mounts on the chassis rails. The front subframe incorporates the engine mounts which would make using the narrowed crossmember difficult. New mounts will be made for the suspension and engine.
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Making The New Diff Mounting Crossmember
The MX5 diff housing has an alloy crossmember with mounts on each end. This was difficult to narrow. Robin thought about using a Ford diff but decided to cut off the alloy crossmember and make a new steel crossmember bolted to the diff housing.
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The Finished Diff Mounting Crossmember
Bushes press into the outer holes and these mount on the subframe. Note the wrap around plates with "rosette" welds (drill a hole and weld through it) on the bush housings.
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New Diff Mounting Crossmember
The rear side of the diff and mounting crossmember
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The Minor With The Floor Cut Out
The floor was cut out of the body and the remains mocked up at the intended ride height. A lot of care and effort went into this stage. Often you will find yourself going around in circles trying to get everything correct. Often a compromise has to be reached. It will be impossible to get every part level.
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The Rear Floor Cut Out
Robin initially cut out as little as possible to retain some rigidity in the shell and in case he needs the inner wings.
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Chassis Mocked Up In Wood
A chassis was mocked up in wood. This allows easy visualisation of how things will turn out and is a lot easier and cheaper to work with than steel. When building a car like this you have to visualise the finished car and work back..... not easy! Mocking up helps. It also allows an estimate to be made of the quantity of steel needed.
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The Rear End Mocked Up
The chassis design is actually very simple. Here you can see just how simple the rear is and how the MX5 subframe just sits under the chassis.
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The Kick Up at The Rear
The chassis kicks up to the rear. However this looks simple but thought is given to where the petrol tank will sit, exhaust will route, where the fuel lines and wiring will go....... remember think of the finished car and work backwards! The intention is to have the fuel tank in front of the rear subframe.
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A Wider View Of The Rear
Note the bracing to keep the body in shape.
Even at this stage we are considering the design of the fuel tank. It will sit between the rails above the subframe (a lot of though went into how to mount it....) and will continue down in front of the subframe with a saddle arrangement over the diff. A sump will be built in and this is where the fuel will be picked up from. Injection engines need a collector pot or sump to ensure a constant supply of fuel. I had a complicated arrangement of low pressure pumps feeding a collector with a high pressure pump, all mounted in the tank. Robin will have just one externally mounted fuel pump. Simple and easy.... the compromise is centre of gravity. His fuel tank will be higher than mine. car building is all about compromise!
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The Front section Of Chassis
The design here isn't finalised as the engine position needs to be considered with thought to the front suspension, bulkhead and pedals.
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The Seat Mocked Up In Position
Robin now has a bucket seat to use for a mock up. A Minor is very narrow and shoulder width is always a problem when fitting bucket seats.
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Engine Sat In Position
The engine is mocked up. Various factors are considered here: for handeling it wants to be as far back as possible but consideration has to be given to the bulkhead position, exhaust routing, sump clearance and engine mounts.
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The Engine Viewed From The Side
There is quite a lot of room in the engine bay and thoughts of V8`s did happen! But it was decided to keep it simple and stick with the MX5 motor.
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New Engine Mount Rubbers
New engine mounting rubbers were bought and these will easily fit onto the chassis rail with a simple bracket. These take up much less space than the original MX5 crossmember.
The steering rack sits on the front of the chassis. The rack required narrowing. This is quite simple and just involved a bit of turning, boring and tapping some threads....... the taps were £70 though.
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The Steering and Pedals Mocked Up
The MX5 lower wishbones go rearwards and compromise the pedal position. Here the pedals are mocked up to see what the seating, wheel, pedal position is like.
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Mocking Up The Seating Position
Consideration is also given to the gearstick position. Often this can be tweaked by modifying the shift mechanism. The steering is put where Robin wants it and not where it just happens to end up. When building a car like this you put things where you want them especially the steering and pedals.
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Building The Steel Chassis
After much mocking up with the wooden chassis it was time to make it in steel. The steel is 100mm x 50mm x 3mm. The intention was to use 2mm but this cost many times more than the 3mm due to being "bright" So it was decided to use 3mm. There will be a weight penalty but the weight is low, it will also make it easier to weld mounts and brackets to. With 2mm spreader plates would be required.
The kick up at the rear is different to the mock up to allow for the petrol tank.
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The Chassis At The Rear
The chassis at the rear above the subframe is very similar to the mock up.
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The Rear End Before Welding Into The Car
This part will go behind the subframe. The design of the exhaust was taken into consideration when making this. We always use Dynomax silencers because they quote airflow figures and the website has dimensions. It is easy to specify a silencer. Robin mocked up a silencer in cardboard to check it would fit.
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UPDATE MAY 2008
Positioning The Front Suspension Jig
The front suspension jig is now used to position the brackets on the front chassis rails.
Great care is taken to get it all square. You always work from a car ventre line and measure
diagonals.
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Mocking Up The Top Suspension Mounts
Robin wanted to mockup the front suspension to check tyre clearances, stance etc. To do this quickly and easily
he used the top mouts from the Mazda crossmember and attached them with 1" box.
This is only a mock up and NOT the way it will be done.
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Steering Rack Mounting
Robins front suspension jig also incorporates the steering rack mounts. The position of the rack
relative to the wishbones is critical for the bumpsteer.
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The Rack Mounted
Robin has already narrowed the rack.
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Rack Mounts
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Lower Suspension Arm Jig
The lower suspension arms are large and go backwards. This compromises the pedal box position. (All car building is compromises!!)
So Robin decided to modify the arms by removing a section. A simple jig was built to ensure alignment.
When making jigs they have to be accurate and strong but they can be quite rough.
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60mm Section Removed
When shortening components it is structurally better to cut diagonally as this gives more weld area and reduces the
stress raiser.
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Wishbone Moved Together
Unfortunately there is a bit of a mis-match when the two halfs are moved together.
You can see how the jig works. The small part is just slid along the close fitting tube.
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Mis-Matched Lower Suspension Arm
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Modifying The Lower Arm
The parts are tacked together and the arm sliced to "bring it in" to match.
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Making The 2 Halfs Match
A bit of tweaking is required to get the two halfs to match.
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Arms Welded Together
The parts are welded together and the welds smoothed.
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Strengthening Plate
A butt weld is not enough. So a strenthening plate is added. The shape of this is also important. The whole aim is to avoid stress
raisers and potential weak areas.
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Shaping The Strengthening Plate
The plate is shaped to go down the sides of the wishbone so it can be welded onto the edges. Also
by making the plate with a bent edge it is stronger.
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Plate With Holes For Welding Through
Holes are drilled in the plate and then welded through onto the wishbone. This is called rossette welding.
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Finished Lower Suspension Arm
The finished arm looks "factory" and should be strong enough.
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Finished Lower Suspension Arm Underneath
The strengthening plate is not welded all the way round as this would cause a stress raiser. Welds are generally
weak points. The plate reinforces the weld underneath.
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Front Suspension Fitted
The front suspension could now be fitted. The top mount is only a mock up and not the intended design.
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Front Suspension Fitted
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View Into engine bay
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Engine Fitted
The engine fits in nicely. Having the components fitted like this will enable Robin to design the
structure for the upper wishbones, top struts, bulkhead and innerwings.
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Engine Mount Template
The engine mount uses an aftermarket rubber and a new mount onto the chassis.
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Gearbox Mount
The new gearbox mount, again using an aftermarket rubber.
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Rear View
The car could be rolled outside for a viewing. Iit is always difficult to see what the car will look like
in a garage.
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Robin Sat In The Car
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The Front Tyre In The Arch
A check was made of tyre clearances. The wheel is not the final chosen style but a cheap wheel bought to allow mocking up.
A little work will be required on the wing lip to get full lock at maximum bump.
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Repairing The Boot Lid
The lower lip of the boot lid is rotten and needs a repair panel.
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The Rotten Outer Part Is Cut Out
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The Rotten Inner Lip Is Also Cut Off
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Different Handle Surround
The handle surround is different so the old one was cut out so it could be welded in.
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Repair Panel Tacked In
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Modifying The Edges
The alignment of the repair panel wasnt perfect so Robin tweaked the edges to get a good panel gap.
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Modifying The Boot Edge
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Welded In
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Welding On The Inside
When welding panels lots of spots or short runs are used to minimise distortion.
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Welding Inside The Boot
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Finished Repair
The welds have been ground smooth. A skim of filler will smooth it all off.
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Chassis Out Rigger
This member wil be the base of the bulkhead and has 2 cut outs for the clutch and brake pedal. The rear lower suspension mount
is on the chassis and if the lower arm had not had 60mm removed this outrgger woud have had to have been further
rearwards compromising pedal and seating position.
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Crossmember Under The Gearbox
A crossmember under the gearbox at the bulkhead is important for chassis structure. Fortunately there
is space to get one in.
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Pedal Box
Robin bought an off the shelf pedal box with the thought it may just bolt in but this was going to be too
much of a compromise in regards to space. Making his own mounts but using the pedals and master cyclinders
would result in much better packaging.
The piece above has hols for the master cyclinders and a pilot hole for the pushrods.
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Pedal Box
All aspects of the pedal box is well engineered. It is good to have high stiffness in all the mounts and structure. This all helps give a good pedal.
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Pedal Box
Twin master cylinders and balance bar are used for the brakes.
