MG Midget K Series Conversion 2 | FAQs Considerations of the Conversion Process
January 23, 2012 at 9:39 PM
As with all engine conversions, there are very many considerations at every stage of the project. This is not intended to be a comprehensive 'to-do' list nor a set of instructions. It's possible to buy all the items needed for a conversion off-the-shelf, from engine mounts to propshaft; the trade-off of course is cost vs. time/convenience.
Here are some of the major considerations:
Choose your engine, based on what performance improvement you're seeking; remember that the effort to install a 1.8 is the same as a 1.4; and a good 1.6 is better than a worn 1.8. It's possible to buy a complete car for less than the cost of an engine off-the-shelf.
Earlier engines (<2001) require the spigot hole in the crank to be drilled to larger diameter; normally the crank should be removed for this operation. Later engines use a sleeve to accommodate the spigot bearing.
Similarly, early 1.8 engines (<2001) require a '1.6' flywheel (determined by the bell-housing); later 1.8s have the common smaller flywheel size.
Make sure your engine is complete with the plenum, fuel rail/injectors, engine loom, alternator, cooling temp sensor, crank sensor, air temp sensor (in #4 runner), exhaust shield, … these items can be surprisingly expensive to buy separately.
If you are retaining the Rover ECU, make sure you have the ECU, immobiliser and crank sensor from the same engine; or have the ECU modified to eliminate the immobiliser function
It's likely you'll use a remote oil filter - there's not much room around the original engine/suspension mounts for the standard KSeries filter
An oil cooler is not necessary for fast road or speed events; consider one for track-days, however.
Fresh K Series engine ready for modification required for conversion
If you will keep the engine unmodified, then you can retain the original Rover ECU.
Note that ECUs are 'paired' with their immobilier/crank sensor; you need to have the immobiliser function in the ECU disabled if you're not sure you have a compatible set-up.
Later (~2001 and beyond) ECUs are different from the early ones, e.g. they can run twin-coil (wasted spark) pack instead of dissy); they are not plug-compatible with early 'dissy' ones.
Early engines can be 'converted' to twin-coil pack by using a later dissy and twin-coil pack and appripriate engine loom.
If you intend to modify the engine, e.g. head or cam change, then you will need an after-market ECU such as Emerald or Omex; an after-market ECU will allow you to fine-tune your engine to deliver more power and mpg for a standard engine, and of course accommodate your further tuning mods.
Gearbox, Bell-housing, Clutch Operation
The Sierra/Granada Type-9 gearbox is the normal choice for KSeries conversions, normally from a 2 litre or 2.8 litre V6.
The choice of bell-housing determines the gearbox you will use, e.g. Caterham 'housings require the 2.8 litre (aka long-shaft T9; for this configuration, the shaft needs to be shortened approx 15mm – but measure this yourself); other housings fit the 2.0 litre box.
Clutch operation may be cable (IMO the simplest), internal hydraulic (the most complex), or external hydraulic; remember that to fix a problem with internal hydraulics, you will need to remove the engine and box.
For cable operation, ensure the cable is always pulled in a straight line from the attachement of the cable 'eye' to the outer clamp; fretting and failure will occur early if the cable entry into the rod/eye moves through an angle as the clutch is depressed. You should check for fretting of the cable at this point regularly at first, to ensure reliable operation.
There's a conversion using a 1.4 SPi that retains the standard Midget 1275 gearbox, with adapter plate.
The choice here is: after-market, modification of Freelander or similar, or bespoke; LHD reduces the space for the headers and a bespoke system will almost certainly be required.
Try to obtain the original heat-shield with your engine; this can be used to protect the starter-motor and alternator.
The starter originally fitted to the engine (actually, the bell-housing) will not work in a rwd configuration, since the starter needs to be fitted on the engine-side of the bell-housing. You will need to source a suitable starter and spacer; the block may required relieving for clearance.
The EFI has to be supplied by a high-pressure pump, e.g. the type used in most cars of the early 90's, delivering 3bar. It's conventional to use a supply and return line to the fuel rail. The regulator at the front of the fuel rail is normally connnected to the plenum so fuel pressure is regulated wrt plenum vacuum. This must be retained for std ECU users, and should be used for after market ECUs, since most maps are created for this configuration. It's possible to regulate wrt atmophere - but the fuel map will be different for low throttle/high vacuum conditions.
It's possible to use a single EFI pump to pull fuel from the tank and supply to the fuel rail; however, this can lead to fuel starvation during acceleration and cornering once the tank is less than ½ full. To overcome this, you should use a low-pressure pump from the tank to a swirl-pot and supply fuel at pressure to the fuel rail from this.
A single line to the fuel rail may be used if the regulator is co-located with the EFI pump. In this configuration, the fuel line must flow well, and the ECU map corrected to run the regulator wrt atmospheric pressue.
The heater-tray needs to be cut back to provide additional room, especially if your engine has a distributor instead of twin-coil packs
The gearbox cross-member middle section is removed to provide space for the larger gearbox
A gear-box mounting plate is required, in place of the cross-member centre
The standard T9 remote unit is ~4 inches behind the original; the gear-lever works well in this position, or you can shorten the remote to retain the original gear-lever position
Many conversions mount the engine to the chassis rails; a better solution might be to use the original engine mounting points on the suspension turret – but the space to do this is limited.
Your engine bay will look something like this; the battery is destined for the rhs of the bay in this picture; other conversions put the battery in the boot:
Engine bay ready for the K…
Here's an engine bay populated:
Jorgen Fisker's bay
Right-hand cars may be converted; the main issue here is the clearance between the steering column and the exhaust manifold:
Arie de Best's conversion; simply the Dutch version of the KSeries Midget
Finally, here's the white engine bay shown earlier but now populated, and back in the workshop after a couple of years for additional mods; it should be said that conversion is a process to be enjoyed on the road as early as possible but realistically is a work-in-progress until perfected:
It's a shame to fit the bonnet
A standard MGF alternator can be used; but modifications are required to mounting brackets to allow it to be positioned very close to the engine to avoid clashing with the suspension turret
You should replicate a Rover cooling system in terms of primary and secondary flow; or use a PRT and follow the Caterham configuration
You should place capillary bulb and ECU sensor into the secondary flow (that is the flow that's not controlled by the thermostat)
Many conversions use a remodelled '1500' type heater to clear the intake filter
Propshaft and Back Axle
Some cars use standard half-shafts and differential, in which case care is needed not to over-stress the system in lower gears (e.g. feathered throttle to minimise wheels-spin and sudden grabbing when grip restored). The quality of half-shafts appears to have varied over the years; shafts that have been used on one side of the car only are stronger than shafts that have been run on both sides.
If you want to use 100% of your performance in the lower gears, you might consider replacing standard parts with LSD and uprated shafts.
Or you might use the principle of: 'upgrade what breaks…'
Do I Need to Upgrade the Suspension and Brakes?
This is not strictly necessary for a KSeries conversion, but highly desirable if the potential of the conversion is to be used safely. Many KSeries Midgets will already have upgraded suspension and brakes ahead of the conversion, use in conjunction with a previous fast-road 'iron' engine. A typical specification might be:
9" or 10" brake disks
Poly bushes throughout
Telescopic dampers throughout
Panhard rod or more sophistaced links for axle location (over undulating surfaces, it's possible to feel the axle in standard setup squirm with applied torque)
Lowered suspension for stability; after the conversion, will need to lower the front again as lighter KSeries engine will cause the front to rise maybe ½" or more
Use 165+ section tyres of an appropriate speed rating.
How do I Wire the Engine/ECU Into the Existing Loom?
There are surprisingly few connections needed: +12v (ignition) and earth; alternator main feed (thick brown) to the solenoid/battery terminal; alternator brown/yellow to ignition warning light; ECU ignition pulse to white/back for rev-counter (or current loop with ignition coil for earlier rev-counter). You should drive a radiator cooling fan via a relay from the ECU. With an after-market ECU, you can wire in change-up light etc.
After market ECUs come with instructions to wire up the ignition, injectors, and sensors for air & coolant temp and throttle position, crank sensor, cam sensor (for VVC), and optional IACV; use the existing engine loom and plugs to simplify this operation. For normally aspirated engines, the MAP sensor isn't used. Strip the loom of the wires not needed.
Despite the pic below, the electrical side is relatively simple:
Wiring it up? Don't panic
Here's the same view, a couple of days later:
Plumbing and wiring nearly finished
How Long Will the Conversion Take?
It's really down to you! For example, one home conversion took 10 days over 4 weeks; other conversions have taken 12+ months, often as part of a body restoration.
How Much Will it Cost?
At one extreme we have a 1.4 SPi conversion, which retained the Midget 1275 gearbox, that cost £120 including the engine. DIY conversions using standard engine typically range from £1.5K to £2.5K. For bespoke conversions with simultaneous comprehensive chassis and brake conversions: the sky's the limit.
What's the Best Way to Start?
Take a look at as many conversions as you can – no two are the same. Speak with the owner: especially if they did the conversion themselves, you will learn how to avoid pitfalls and hopefully choose the easiest path for your conversion.
Chartered engineer with MG Midget experience from June 1974. Now enjoying my 3rd MG Midget, a 1973 RWA, acquired end 1977. Converted to KSeries power in March 2002, it achieved class awards summer 2002 at Prescott and Curborough.
With a high level of enthusiasm for these cars, especially the KSeries conversions, I was invited by the forward thinking Midget Register committee to be KSeries Registrar; this gives me a unique opportunity to encourage more conversions to use the wonderful MG-Rover KSeries engine and enjoy the company of other KSeries owners in conjunction with their remarkable cars.