MG Midget Powertrain Swap

Over the past few summers I decided to work towards gaining a broader and more practical understanding of cars, so began a personal project to replace the original engine in a 1975 MG Midget 1500 with a Rover K-Series engine.

The project has involved plenty of research and sourcing of components.

The first stage was to remove the original engine, gearbox and drive shaft. A crack in the chassis was discovered and repaired. A Ford Type 9 gearbox and a MG ZR 160 donor car were sourced and the engine was then removed from the ZR. With some modifications to a bellhousing and clutch arm the engine was mated to the gearbox.

The Midget body required modification to fit the new powertrain, so modified parts had to be designed, fabricated and then welded in place. The engine block itself needed modification to accept a new starter motor, which was tested in place.

Further modifications to the engine block and Midget body were needed after trial fitting the new powertrain, iteratively reducing the engine height until the original front end could be fitted without fouling the VVC mechanisms.

As a chassis crossmember was removed to accommodate the taller gearbox, a considerably strong gearbox mount was designed and fabricated that would keep the car rigid.

Alternator mounts have been modified to fit within the Midget wings. Bespoke engine mounts have been fabricated, and a new layout of the cooling system implemented. The Rover engine loom has been stripped back and integrated into the car, retaining the ECU and immobiliser systems.

A dual pressure fuelling system has been implemented with a swirl pot to reduce fuel starvation. An oil filter take off block has been designed and fabricated to relocate the oil filter due to space issues. The rear halfshafts have been replaced with competition spec to prevent shearing from the increased torque, and the differential replaced with a clutch type limited slip differential.

The car has successfully run and driven.

The next stages are:

  • Fixing a few electrical issues such as non working lights.
  • Replacing the interior.
  • Fixing minor oil and coolant leaks.
  • Modification of the original heater system to fit in the reduced space.

After that it should be good for its MOT!

The final car should be in the region of 170bhp with stock ECU (estimated 10bhp over standard due to larger exhaust system and removal of catalytic converter). The car will weigh in the region of 780-820kg.