Every MGF and MG TF alternator is an 85-amp unit, regardless of engine capacity, transmission type, or air-conditioning fitment. What changes across production is the physical design of the alternator itself.
Early cars use a Lucas A115i unit, fitted to MGF manual cars without air conditioning up to VIN YD522572 and continuing on all MGF and MG TF manual cars with air conditioning throughout production. Later cars use a GCB2 unit of equal 85A output, introduced on MGF manual cars without air conditioning from VIN YD522573, fitted to MG TF manual cars without air conditioning, and fitted to all MGF and MG TF automatic cars. The two designs are not physically interchangeable, they use different mounting arrangements and different pulley types, so ordering requires knowing the car's VIN, transmission type, and air-conditioning fitment.
New and Reconditioned Exchange
Alternators are catalogued as new units and as reconditioned exchange units, with the exchange option priced significantly below new. Exchange represents a significant saving where the alternator's external housing is sound but the internal components, rotor, stator, diodes, voltage regulator, or brushes, have reached end-of-life. The old unit is returned as a core and remanufactured to original specification by specialists. A failing alternator typically presents as a dashboard battery warning light, a gradually discharging battery despite normal driving, or in more severe cases complete charging failure.
The EPAS specification of the MGF and MG TF means a charging failure must be addressed quickly, a fully charged battery can be drained within about 25 miles of daylight driving by the EPAS pump alone.
Drive Belt, Two Lengths by Air-Con Fitment
The alternator is driven by a polyvee (multi-ribbed) ancillary drive belt from the crankshaft pulley. The belt is catalogued in two different lengths depending on air-conditioning fitment. Non-air-con cars use the shorter belt, which runs only around the crankshaft pulley, tensioner, and alternator. Air-con cars use a longer belt that additionally routes around the compressor pulley.
Ordering requires knowing whether the car has factory air conditioning fitted, the two belts are not interchangeable. Note that on the K-series engine, the water pump is driven by the timing belt, not by the ancillary drive belt, so a broken ancillary belt does not cause immediate overheating the way a broken serpentine belt does on many front-engined cars.
Tensioner, Mounting and Heatshield Hardware
The drive belt is maintained under correct tension by an automatic spring-loaded tensioner pulley, catalogued individually along with its retaining nut. Alternator mounting consists of a main mounting bracket (different on air-con cars to route around the compressor) with an adjusting link to set initial belt tension at fitting. The alternator is retained by M10 through-bolts and nuts at two positions, the main bracket pivot and the adjusting link, all catalogued as individual items. A heatshield protects the alternator from exhaust manifold heat, retained by M6 flanged screws, and the heatshield mounting bracket is itself catalogued separately.
Access from Underneath
The mid-engine layout means the alternator is accessed from underneath the car with the undertray removed, rather than from above. This makes a roadside alternator belt replacement unrealistic, the car needs to be on ramps or a lift, but once access is arranged the change itself is straightforward. Drive belt condition should be inspected at every service; a cracked, glazed, or frayed belt should be replaced on condition rather than left to fail.