Day 6: What’s in a Spares Box?

Day 6: Drawer 6: Nuts & Bolts, Drive Springs & Couplings


A few odds and ends thrown into this box, so I shall stick to the essentials. Whilst not durable spares, the spares you find here are very much ones that you might need one day. The odd nut or bolt can go missing, and being imperial, they will become increasingly more difficult to obtain (although should still be available if you search hard enough) The drive springs (and couplings) can either twist out of shape (in the case of drive springs) or split (in the case of drive couplings). For more detail, let’s delve in;

Top left (and the compartment below top left) you see 8BA nuts and bolts as used on the Poole Farish chassis (except for the class 87/90 chassis). It’s worth having an assortment of these up your sleeve if you plan on taking your chassis apart – you might just need one if one gets swallowed up by the carpet monster! Whilst you can buy in serious bulk from places like here I find it easier to contact BR Lines and just ask for an assorted bag (60 in a bag) for ten pounds. That way you know you’re going to get a few of each. They are not listed on the website so you would have to enquire directly for these.

Second in from the left we see drive springs. These are not to be confused with coupling and brush springs, which are small copper springs (the drive springs being steel I believe). The job of the drive spring is to connect the armature shaft to the lay shaft (the shaft with the worm gear on it). By acting as a tight fitting sleeve over both the armature and lay shafts, it makes a coupling between them, so that when the armature rotates, this rotary motion is also transferred to the lay shaft. They require precise longitudinal alignment (to be covered in a later article) and once set shouldn’t give you any problems. That said, they come in handy if you are working on an older loco which has drive couplings (instead of springs), since then you might wish to swap out the couplings for springs.

Next to the drive springs you can see the white plastic (used) drive couplings. These performed exactly the same function as the drive springs – transferring the rotational force of the armature shaft to the lay shaft. The difference with these is that instead of being a spring coil, they were a female and male peg arrangement. Whilst they worked effectively, they suffered from the following; 1) much noisier than the springs 2) tended to crack where they attached to the shafts, leading to a loose fit and hence ineffectual transfer of rotational force 3) did not allow for slop adjustment (changing the overall length of the shaft, which is possible with the springs). I personally try to swap them out for springs, only really opting to keep them if I want to keep a loco completely original. These drive couplings were used on earlier Poole models and there would be no real need to acquire them now – if indeed they are still available, which I do not believe they are.

The rest of the top row consists of some used nuts and bolts (rusty) and some used drive springs. Nuts and bolts tended to rust when the locos were kept in damp conditions. I try to clean them by first leaving them in white vinegar overnight, and then wiping the rust off with an oily piece of tissue. It works, but you probably won’t get them completely rust free. Still, worth keeping for a future project.

Middle row, second from left you see some rather longer drive springs (also visible on the bottom row on the right). These are for the class 87/90 chassis and instead of attaching two shafts together, these extend outwards from the armature and actually mesh with the pinion gear themselves. The lay shaft and worm gear are completely done away with. Not listed by BR Lines but they should be available if you contact them directly.

Finally, on the left of the bottom row, we see some even longer springs. These are for the class 158/159 and do exactly the same job as those in the class 87/90. They were known to jam up. Again, available from BR Lines if you ask.

So, why did Graham Farish use this elongated drive coil method (instead of the lay shaft and worm gear) on their class 87/90 and class 158/159 models? I thought it was down to better creep and speed control, since I do notice less inertia when a loco is setting off. However, a friend mentioned another reason which made me think the other day – cost. Interesting, what do you think? Comments below please.

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