The picture at right shows a common problem of misalignment of the dynamo pulley on the MGA Twin Cam engine. Note that in the close-up photo the parallax error makes this misalignment appear to be greater than it really is. The misalignment is usually no more than the width of the belt. The Twin Cam uses the same basic dynamo body as the push rod engine, the iron end plates on a Twin Cam generator are similar in configuration to the alloy end plates, the fan is the same as the smaller diameter fan on the 1500 engines, but the Twin Cam pulley is iron rather than stamped sheet metal riveted with alloy hub. The problem here is fitment of the wrong fan and pulley (or a complete dynamo from a 1600 pushrod engine).

The fan in the picture at right is too thick (with slightly offset center hub), and the sheet metal pulley has too much forward offset. Compare that to the pictures below. When the correct thinner fan and iron pulley are used the pulley will sit closer to the front plate.

The Twin Cam pulleys have different configuration. Both pushrod and Twin Cam engines called for two different pulley diameters (and different length belt to match) at various times in production. The first 171 Twin cam engines had 4-3/4-inch diameter pulley, while later ones had 4-inch diameter pulley (still larger than the pushrod engines). The pulley construction is also different with the standard pulley(s) being composed of two sheet metal stampings riveted to an alloy hub where the Twin Cam pulleys are one piece iron material. Pulley groove offset from face of fan is a bit less with the Twin Cam pulleys.

Note that fans used in various applications can also be different. The 1500 type (C39) generators had the adjuster bracket screw located slightly closer to the armature axis and used a smaller diameter fan. Installing the larger diameter fan on the earlier dynamo can cause the fan blades to foul on the adjuster screw. Notice in the first picture above that this particular (too thick) larger diameter fan has notches in the rear corners of the blades that would allow this larger fan to be mounted on the earlier application dynamo. This fan is however incorrect for any MGA application. The fan for the 1600 model changed from 4-1/2" to 4-7/8" diameter and from ~.400" to ~.470" thick and has 1/8" offset in the center hub area rather than flat, but still no notches in the fan blades. When the 1600 type fan with larger diameter (and no notches) is installed the later style end plate must be used (with the adjuster screw farther out).


The Twin Cam dynamo was a C39PV-2, "modified for the application" and had Lucas part number 22295. The modification is apparently only the front pulley (and iron end plates), but you do need to use the correct small fan.