The MGC uses a three-point power unit mounting system, two front engine mountings and a single rear gearbox mounting. This arrangement is shared in principle with the MGB, but the front engine mountings are positioned differently to accommodate the longer and substantially heavier C-series six-cylinder engine within the modified engine bay. The additional weight of the six-cylinder unit, approximately 650 to 700 lb compared to the MGB's 360 lb, places considerably greater demands on the mounting rubbers, and perished or collapsed mounts are a common source of vibration, drivetrain misalignment, and secondary component fatigue.
Front Engine Mountings
The front engine mountings are bolted to the deep U-shaped welded-in crossmember that also carries the torsion bar front suspension mounting points. This is a fundamental structural difference from the MGB, where the engine mountings are attached to a separate crossmember carrying the coil spring front suspension. The MGC crossmember is integral to the bodyshell and is a far more substantial structure than the MGB's, reflecting the combined load of the six-cylinder engine and the torsion bar suspension forces. MGC front engine mounts are not interchangeable with MGB items, as the rubber dimensions, stud spacing, and mounting geometry all differ.
Rear Gearbox Mounting
The rear gearbox mounting is located at the underside of the gearbox extension housing and connects to a crossmember beneath the transmission tunnel. Together with the two front engine mountings it completes the three-point suspension of the power unit, absorbing both the weight of the rear of the gearbox and the reaction torque transmitted through the drivetrain under acceleration and engine braking.
Inspection & Replacement
Mounting rubbers should be inspected regularly and replaced at the first sign of deterioration, looking for cracking, compression set where the rubber has permanently deformed under load, oil contamination which softens the rubber, and any visible separation between the rubber and its metal bonding plates. Failed mounts allow excessive engine movement that can affect throttle linkage alignment causing erratic idle and throttle response, exhaust manifold cracking from the manifold being forced against the downpipe flange, cooling hose fatigue from constant flexing, and fan blade contact with the radiator cowl. On the MGC, where the heavy six-cylinder engine amplifies all of these effects compared to the lighter MGB engine, timely mount replacement is a particularly important maintenance item.