Below we can see the dimensions, courtesy of the Graham Farish catalogues, for the type I/II armatures. Whilst these dimensions are useful to know, the armatures should be a close fit in the chassis available and adjustments to either the armature or chassis shouldn’t be necessary.
There are some important distinctions to be made, however, between the early copper commutator versions (produced up until 1993) and the later silver commutator versions, produced after 1993. Below we can see what appear to the newcomer subtle differences, which in fact are important to understand.
1. Copper commutator produced from 1984-1993. Prior to 1984 this was also produced as a 3 – pole variety.
2. Silver commutator produced from 1993 – 2001 (end of UK production).
3. Bachmann armature used in those chassis which still utilised a Poole Farish design, such as the class 08 and 20 diesels.
The important difference between 1. and 2. is that the earlier copper commutators had flatter wire connections from the armature windings which were crimped into place. On the later, silver, commutators we can see the wires are soldered onto upright posts, you can see just to the left of the silver commutator in the picture below a black rim with soldered blobs on it. The effect of this was to make the diameter of the rotating commutator section larger, which led to clearance issues with the earlier chassis and chassis base plate basically preventing rotation. Hence, trying to fit a post 1993 commutator to an earlier chassis requires modification to the chassis & base plate.
Below is an interesting illustration of the note that Graham Farish included with their armatures post 1993, in order to advise customers of the difference in dimensions.
Please note that the Bachmann produced armatures, whilst backwards compatible with the Poole produced chassis, had different dimensions again. This is noticeable in the shorter commutator. The main concern here is aligning the commutator correctly to the brushes. This shall be discussed at a later date.