The Guide to Building a Rhubarb Roadster

Build yourself a Rhubarb

So you have either taken the plunge to purchase a kit or you are looking to see what the process is to start the building of a Rhubarb Roadster Kit Car. We tackle this in a couple of stages, so once you have made the decision to build your own car, firstly you need to establish what specification Mazda MX5 donor car to purchase. Will it be a 1600cc or an 1840cc series 1 or 2? Do you buy a damaged one or what do you buy? There are significant differences in vehicles so spend some time to ensure you get what you want. If you’re unsure what your best options are, the Rhubarb Cars team can help.

You will see on the form used to order your kit, should you be looking for performance upgrades this information is required.

 

Stage 1

You now have yourself a Mazda MX5 donor car. These cars are relatively easy to strip out and things you don’t require can be sold if in good condition.

Here’s a list of items that you need:

  • The complete running gear, front and rear sub-fames complete with everything that is on the original car except for shocks and springs.
  • Engine gearbox, drive shaft, transmission torque arm, speedometer cable and throttle cable.
  • Take all the brake and fuel lines off the body of the car if these are not damaged. These can be re-used if required, or you can make new ones.
  • Although you don’t need the fuel tank, you will need the sender and pump unit along with the complete filler piping unit.
  • The wiring harness or electrical loom can be used so take it out. Should you not use it, you will probably require some of the connectors.
  • Remove the instrument cluster, steering column and steering wheel.
  • Remove the brake and clutch cylinders including the brake booster. Take out all the pedals and the hand brake assembly leaving the cables still attached to the rear sub-frame.
  • Take the overflow bottle for the radiator and the radiator hoses as if they are in good condition, you may be able to re-use some of them, or just buy new ones.
  • Remove seats, but you will need to replace the seatbelts for compliance. These can either be standard web-grabber belts or motorsport 4 point harnesses.

IMPORTANT: SAVE ALL THE BOLTS, WASHERS, NUTS, PLASTIC CLIPS, HOSE CLIPS. You will need many of them.

 

Stage 2

At this stage you should have ordered your Rhubarb Kit and will have an expected delivery date.

Until it arrives, you need to get on with deciding how much reconditioning is required to parts you have taken from the donor car. This is an individual thing as in some cases the parts from the donor car can be just cleaned, checked for condition and made ready to be installed. However, we have found that most kit car builders are doing it as much for the journey of building their own car as for the pleasure it will give them when it’s finished. Therefore, they take pride in doing the best job possible within their budget.

So, strip it down to the level that you want, clean it, paint it or have it powder coated. With bolts etc. you can have them zinc coated or just clean them up. Also at this time you need to assess whether there are any modifications or repairs required. Remember, when you ordered your kit there were performance options available where some modifications may be required. These need to be done prior to painting or powder coating. This process is a great way to understand how it all works and how all those bits you have fit back together. Once everything is looking like new, you can go about assembling your sub-frames ready to be bolted straight into your new chassis.

Extra to be done:

You will receive two new top front suspension arms in the kit. You will need to have the bushes and ball joint from your old arms pressed out and re-fitted to the new arms prior to assembly. While you have everything apart, you need to remove the backing plates from all the brakes so that mudguard brackets can be fitted. 

 

Stage 3

Fitting the body

There are two schools of thought when it comes to this stage. This can be done prior to the chassis being powder coated, (this is recommended) or this can be the last stage once the car is fully assembled. So it’s over to you at which stage this is done. It is suggested that you review your build plan and do what suits you and your budget.

During the fitting process, minor adjustments may be needed to some panels for a more exact fit.

Nose

Starting with the nose onto the mounts with the rubber sleeves in place, push nose fully back and centralise on the chassis (sighting using the light/ARB mounts). Now slide the collars up to the nose mounts and tighten the grubscrews. It is a good idea at this point to attach the side latches to make alignment with the console easier. The main part of the latch goes on the nose.

Console

Next place the console on the chassis up against the nose. It’s helpful to have fitted the latch assembly prior to this to hold the two sections together. (Note, latch plate on the console.) Centralise the console on the chassis and mark and drill the 4 mounting holes (Make sure the nose is still fully back in its mount. Also you may need to pack the front console mounts should it be needed.) At some stage you will need to cut out the marked area for the instrument cluster. Insert the cluster from the rear ensuring that the 4 mounting lugs are against the panel before marking and drilling. The instrument shroud can now be marked and drilled as it uses the top two holes.

Rear Bulkhead Panel

Moving to the back, the rear bulkhead panel sits directly on top of the rear bulkhead cross member and against the rollhoop. Mark and drill the 4 mounting holes. Carefully measure and drill centre mounting hole which also secures the tail mounting tongue. (If you are using 4 point harnesses, you will need to make cutouts to suit the mounting points in the bulkhead.)

Rear Body

Fit the rear body mounting frame as per photos, ensuring the frame is centralised, which can be achieved by diagonal measurements. Sit the body on the frame and adjust cross tube so that the mounting pads are flat against the body and also adjust the two struts to achieve a good fit and centralisation. Mark the 5 fixing holes and drill to 6.5 mm. Refit the body section and check the hole alignment before increasing to the stepped washer diameter.

Rear Wing

Fit the wing uprights through the slots until they’re against the body and mark and drill the 4 mounting holes. You can now bolt the uprights in position and fit the wing and endplates.

Front Wings

The fitting is done with the car on a flat surface set at approx 115 mm ride height. Measure up 270 mm (or higher if you wish) from the ground using a square for accuracy and 420 mm forward of the top wishbone bolt. You now need to bore a 35 mm hole for the wing tube bush using a holesaw at 90° to the car’s centreline (not 90° to the body!). With the bushes fitted and tube centralised, slide the wings on and shape the inside edge if necessary to match the body profile. Drill and attach the adjuster brackets to the trailing edge of the wings and set wing angle to approx 3° (ensuring both sides are the same) and drill 6 mm fixing hole in body. You can now drill through the hole in the wing underside to attach to the tube with rivets. You may want to silicone the tube bushes to inside the body.

Splitter & Grille

Fit the front splitter and position the bottom of the grille against it. With the top of the grille firmly in position, you can apply some clear silicone to the back edge to retain it. (If you are using the front wing option, then the splitter may need the sides shortened.)

 

 

Stage 4

Preparing chassis for assembly

  • By this time you should have also decided what finish you want on your chassis, sub-frames and suspension components.  Whatever you have decided, it is recommended that the  chassis is sandblasted before your finish product is applied. Where you have decided that other components are to be powder coated, these can also go for sandblasting prior to  powder coating. Remember, if you are having performance upgrades ensure that the necessary engineering work has been carried out.
  • Also at this stage if you are getting other parts powder coated, such as light brackets, mud guard brackets, coil springs and any other items, include them as a job lot. Note, to save  retapping holes, it is advisable to block off threaded holes with old bolts and studs should be either taped or covered with silicon tube.
  • Remember to list what you deliver and give a copy to the contractors.
  • Another item that can be ticked off is what finish you want on your nuts, bolts, washers and any other small items used in the assembly process. Should you wish to have them zinc  plated, ensure that any dirt, grease or paint is removed. Make sure that you have all the bolts etc that you will require; if in doubt get a few more done.

 

 

Stage 5

Brake and Fuel lines

Brake lines

can depend on the work shop facilities you have. For example if you have a hoist,  this can be done at any time prior to the engine and gearbox being fitted. However, should you not have access to a hoist and you are doing them yourself, there could be difficulty in  raising the car to a reasonable height so you might need to do this in stages prior to the sub-frames being fitted. The only connection to a sub-fame is at the rear.

 

 

 

The making and installation of the brake lines is normally done in one step. As to when this is done

  • Firstly you need to install the brake booster assembly.  Then take the stainless steel brackets provided and the plastic clip-on blocks usedon the donor car brake lines. Clip the bracket  and block together and attach these to the tunnel rail. There are 6 of these and they provide the attachments for the one brake line and two fuel lines. The brake line goes to the top  of the bracket so ensure the smaller of the clip points is to the top when these blocks are assembled.
  • Run the rear brake line from the master cylinder down into the drive line tunnel and attach to the clips ensuring that the line has sufficient clearance to the chassis when negotiating a  change in direction. At the rear sub-frame the standard connection block is used to complete the circuit.
  • Positioned below the master cylinder on the lower outer chassis rail is a bracket where the flexible brake line from the caliper is secured. You need to make up the short pipe that comes from there up to the master cylinder attachment point.

The same applies on the left side where the left front brake line comes down from the master cylinder onto the diagonal chassis bar which then leads back up to the front bulk-head. Try and have the pipe on the underside of this bar. The pipe then should be at the bottom of the upper front panel and you can use the rivet holes as fixing points as you cross over to the LHS then down under the opposite diagonal bar to the point where it needs to make its way down to the fixing bracket provided.

Notes

In fitting these lines there is a reasonable amount of flexibility so the key objectives are to make it look nice, not interfere with the body work or have contact which may lead to damage.
It is better to make the lines a little longer if you have concerns on your lengths as it is quite easy to lose length by making bigger turns
All lines are to be secured at no more than 300 mm intervals where you can use Plastic “P” Clips or clips of your choice

Should you wish to run a proportioning valve other than the standard option this will then require a different lay out.

 

 

Fuel lines

  • Starting at the front, you have two flexible hoses coming off your injector rail on your engine. The front is inlet and the
  • rear is the return. You want the new steel lines to start where  they can be connected to these hoses. You can always allow extra and cut off.

  • Follow the same process and attachment as the brake line. In fitting these lines there is a reasonable amount of flexibility. The key objectives are to make it look nice, not interfere  with the body work or have contact which may lead to damage.
  • The fuel filter is mounted on the rear bulk head panel just in from the RHS bottom seatbelt mounting point.  You will 
  • find 2×6 mm holes where the standard filter fits. It is  recommended that a new filter is fitted. The high pressure fuel injection hose connects from your new lines to the filter then on to the fuel tank. Check that the direction of flow is  correct at the time of fitting the pump unit to the tank.

Notes

For those who wish you can straighten out the lines from your donor car and refit them. Care is needed but it can be done.

It all becomes a bit close at the bottom where you turn into the tunnel from the engine bay as you will also have the clutch release mechanism and speedo cable in this area. Take your time in getting this nice and tidy through here. Refer to pictures on Website.

 

 

 

Stage 6

Fitting of Aluminium panels

  • Drill chassis for fixing of aluminium panels. Start by positioning each panel one at a time in its correct position, clamp in position and drill holes with a 4 mm bit. Use panel pins if you  have them or place a rivet in holes about 300 to 400 mm apart in order to keep it in alignment. Do a quick check to ensure that all other holes in the panels allow clear access to any  fixing points in the chassis
  • When fitting and drilling the transmission tunnel panels, it is suggested that you start at the back and work your way forward. You will see that there are some fixing holes that will  need to be drilled into the panels
  • Prior to fitting the rear transmission tunnel, rivet into place the steel handbrake mounting bracket.

 Once all holes are drilled, it is recommended that each hole is de-burred in order to leave a smooth finish.

  • Now you are ready to apply the adhesive and rivet the panels onto the chassis. Using the rivets and adhesive supplied, off you go. First place a bead of adhesive on the area of the  chassis you intend to fix the panel to, line the panel holes with the chassis holes using panel pins if you have them. Where panel pins are not available, clamp the panels lightly to the  chassis and use the rivets to align the holes before commencing riveting.

Note

 When riveting is completed on each panel, wipe away any excess adhesive. As outlined under the brake and fuel lines, your individual assembly process may require that certain panels such as the front and rear bulkhead panels be fixed early on.

 

 

 

Stage 7

Sub-Frame installation

With all components back and any reconditioning, powder coating or painting of other components completed and assembled, they are ready to install onto the frame.

  • The front sub-frame is attached to where the main chassis rails intersect on the front pedestal mount. Use the bolts with a spring and flat washer and fit loosely in place. There are  two further bolts required to be inserted at the back of the sub-frame up through the front bulkhead with nylock nuts fitted. Once these are in place, tighten all points.
  • The sub-frame will need to have the steering rack in place as there are two stays that mount from the back of the sway bar mount down onto the top of the steering rack front mounting point.These must be in place when the sub-frame is installed as they are an integral part of the deformable front structure and eliminate movement of the front portion of the chassis. 
  • The rear sub-frame is attached to the chassis with 4 bolts with spring and flat washers. Depending on rear sub-frame performance upgrades, you may also have a series of bars that  will attach to the sub-frame and chassis. At this point you are not fitting the torque arm that connects from the diff to the gearbox.

 

Once you have the sub-frame in place, you can connect up the hand brake, which is a direct retro fit from the donor car.

  • At this stage you can assemble the front and rear shocks, springs and bump rubbers. To start set the spring height by measuring from the bottom of the thread to the bottom of the  spring when the platform is screwed up putting pressure on the spring.  For the Front, start at 40 mm, with the Rear at 120 mm. This is just a starting point and may alter once the car  is ready for its wheel alignment.
  • You can also fit the steering column and clutch cylinder with the pedal arrangement. The steering column has a “C” type bracket welded at the end of the tube base. This is to be  removed and is replaced with the collar bracket supplied that will slip over the end of the steering column tube. Be careful not to damage the tube in this exercise.This will then bolt on to a small bracket above the hole in the bulk head. It is adjustable in order to gain the correct position. The top mount is as per the donor car and can be height adjusted by shims.

 

 

 Stage 8

 Engine and gearbox

As part of your cleaning and reconditioning we would recommend that at least you replace the gearbox tail shaft seal, the rear crankshaft main seal and the Cam angle sensor O ring seal. To align with any performance upgrades the clutch should also be upgraded. When you have the gear box off the motor, there is an aluminium lug on the left hand side at about the centre of the bell housing. We suggest you cut this off as it allows easier installation and removal. With that all done and the motor and gearbox together, the unit will slip straight in. It is ideal to have a second pair of hands to help guide things together at this point. Once in place fit your torque arm with the new drive shaft hoop in place, bolt in your driveshaft and the drive train is in place. The kit also contains a flat chassis brace which attaches to the chassis towards the rear of the gearbox. Note: Refer to the photo for the drive shaft hoop position.

 

Stage 9

Radiator

  • With your radiator kit you will have a fan which has been attached to the radiator. Install the radiator then fit the aluminium shroud. You may be able to use the original top hose but  you will need to get a suitable right angle hose for the bottom.
  • The overflow container from the donor is normally used. As there can be a couple of different types, there are two options available on the chassis. Refer to Photos on the Website for  clarification.

 

 

 

 

Stage 10

Fuel Tank

  • This fits down behind the roll bar with the filler on the LHS and requires the cushioning washers supplied placed between it and the chassis when installed.
  • The fuel pump and sender unit require a couple of small mods prior to installation. Firstly the sender needs to be rotated 180°in order to function in the new tank. The fuel filter on  the pump needs to be changed and this is pretty straightforward. The wire mechanism that the sender unit float is attached to is required to be changed so the gauge will operate  correctly.  With these items done, the unit can be installed and the fuel hoses to the filter and return line can be completed.
  • The fuel filler and breather require a little more work and you need to refer to the photos as you need to cut not only the metal part but also the filler hose of the donor car. Use the  small stainless steel bracket which attaches to the diagonal bar coming down off the roll hoop. Once you have this lined up with the hole in the tail section


Note: attach the bracket to the  diagonal bar either by rivet or tapping a 4 mm hole.

There are several different configurations of sender units: all of these can be used and all have a variation. There may be a need for some re-engineering so care is needed to ensure the pick-up is located correctly in the collector.

 

 

Stage 11

Electrical

You may need to get assistance in this area as you can use the loom and instrument panel from your donor and then modify the loom to meet your needs. Where you are going to run a programmable ECU you will need the appropriate wiring upgrade.

 

 

 

Stage 12

Mudguards

Front


  • You need to bolt the triangular plate on to holes that were used to hold the brake backing plate. From this you will attach the forward bracket. The rearward bracket will bolt onto the  standard bottom caliper bolt. This is repeated on the other side. Before attaching the guard, you need to check that the front mount has clearance between the top suspension arm on  full lock. At this point tighten the front mount as its position is set. Note: Check that the rear mount doesn’t foul the brake line on full lock.

Rear

  • The forward rear bracket uses the two caliper mounting points. With the rearward mount you will have received a drilling jig that you clamp into place on the outside at the bottom  of the upright.  It fits neatly into the cast indentation allowing you to drill the 8 mm hole required to fix the fastening bracket on the inside of the upright. From there you are able to  attach the mudguard mount. This is repeated on the other side.

 

Guard attachment

You will need to make yourself a simple jig that will assist you in this and enclosed with the fitting kit is a diagram. There are also photos on the Website. With the mount bolts just nipped tight, place the guard over the wheel and up against the mounts. With your jig (2 blocks 30mm x 30mm x 150mm, 500mm apart), you should have a tyre to guard clearance of  30 mm between the top of the tyre to the inside of the guards. Once you are happy with the positioning, mark and drill the 6 mounting holes and attach your guard.

 

 

 

 

 

 

 

 

Stage 13

Wheels and tyres

The car has been configured to use up to a 15×7 rims with 205x50x15 rear and 195x50x15 front size. The centre off-set on the wheel will depend on whether you require wheel spacers or not. Should you choose to go for the likes of a Wilwood 4 pot caliper and disc upgrade, you will need 15inch rims.

The common wheel size used is 15×7 with 35 mm to 40 mm off-set and 100 mm PCD with a 25 mm wheel adaptor. You can use standard wheels with adaptors.

 

Stage 14

Exhaust system

Where required, RCNZ can supply mufflers and the required catalytic convertors. This is another area where you may need assistance if you don’t have the necessary equipment or skills to carry out the fabrication of the system.

There are 4 mounting points that are recommended. Three of these are built into the chassis, two at the back of the chassis and one on the rear bulk head just as it enters the drive line tunnel. For these you can use the same rubber mounts from the donor. The fourth, which is optional, requires some minor fabrication and can be attached to the rear of the gear box where a small bracket attaches to the gearbox or you can use a bracket off the bell housing. 

 

Stage 15

Final bits and pieces

The majority of these are simple installation issues and the following list is a guide for you:

Lights

The park/indicator lights are attached beneath the headlight bracket by 2 self tapping screws. Headlights are bolted to the mounting plate. Note: these are a dipped only headlight: there is no high beam.

There are two indicator repeaters to be attached to the side of the console (these are not mandatory). The rear taillights are fitted with the indicators to the outside and the number plate light centrally at the extreme top of the number plate recess. The high stop light is mounted central above the number plate recess. The two reflectors should be mounted centrally at the bottom of the rear guards.

Mirrors

The mirrors can be bolted directly to the console face to suit.

General

 

Bleed brakes and adjust hand brake. Fit the speedo cable. Fit throttle cable. Mount instrument panel into dash panel (if you have not already done so). Adjust pedal heights to suit. Fit gear lever and rubber boot. Fit seats and new seat belts (where motorsport harnesses are being used, slots will be required in the bulkhead panel). Fit and secure battery. Fit front light mounts directly on to the front sway bar mounting points. Fit all the lights etc to the appropriate body parts. If you are running power steering, the reservoir can be mounted to the LHS of the firewall bulkhead.

Stage 16

Chassis set up

  • Shocks from full soft start with 4 clicks on front and rear, increase for a firmer ride decrease for softer.
  • Standard sway bars have no adjustment; however, it is recommended that a firmer bar is used on the front.
  • Front ride height is measured under the front cross member and should be approx 115 mm. Rear ride height is measured from the centre of the lower suspension arm’s inner  mounting bolt and should be approx 180 mm.
  • Front toe should be 1 mm toe in to 1 mm toe out, rear toe .5 mm to 1 mm toe in.
  • Camber with front at between .5° to 1° neg and rear .5° to 0° pos.
  • Caster with power steering should be 3° to 4°, where non power steering is being used, err on the lower side.
  • Tyre pressures. Remember we are dealing with a weight in most cases that is below 700 kgs, so in road mode you need to experiment as to what suits you. However, 18 to 20 psi is a  good starting point (this will vary depending on tyre size and type).

Note: These settings are a starting point for your certification; you may find your driving style or the type of use require different settings.

 

“At Rhubarb Cars we want to ensure that your build meets and hopefully exceeds your expectation so we are on call to assist in any way required. We are also able to provide engineering services you may require.”