When Scalextric designed and made the injection mould tooling for the Ford XR3i models they made an error in positioning the motor mounting points. Essentially placing the rearward motor mounts too far forward on the chassis leading to a mismatch with the gears, see the pictures above. This problem also affects MG Maestro models that share the same chassis moulding.

The lower restored Ford XR3i chassis shows the motor mounts of the original chassis tooling. However, this positioned the motor too far forward in the chassis and the motor shaft could disengage from the alignment groove in the centre of the black rear axle (contrate) gear. The axle could then move from side to side and disengage with the motor pinion gear, thereby loosing drive.

The lower chassis also shows how Scalextric remedied this problem, at least on a temporary basis. A washer was placed between the motor body and the forward motor mount pushing the motor rearward and into engagement with the contrate gear, crude but effective.

The upper un-restored Ford XR3i chassis is from a later car and shows that the motor mounts have been moved. The later chassis does not suffer the drive disengagement problem of the earlier chassis.

To our knowledge this chassis error is only seen on the C307 and C308 XR3i cars and the MG Maestro C310 and C332 cars. Do you know more?

Another chassis tool modification can be seen where the front of the chassis clips into the body. This clipping feature is far more pronounced on the later (upper) chassis.

Both the earlier and later chassis mouldings are marked on the underside with the moulding number L5844.