The other day I got the now rare chance of a quiet running session and started with the newest unit to traffic, the Met Cam lightweight or Class 101.

After a few runs and stops at Birch Vale station, the unit slipped as it started out of the platform; the ability of the traction unit to haul its train was non-existent. Inspection while still on the track and powered up, showed that only one axle was spinning.. A need to strip body from under-frame and have a closer look at Lima's pancake motor driven transmission.

I still have difficulty in believing what I found! - the last but one sprocket of the drive train, i.e. that which drives the sprocket fixed to the axle, had left its stub-shaft; so one set of wheels was no longer being driven; - no wonder that the sole driven axle would not move its train!

Inspection revealed that its partner for the second axle was in place but could quite easily be eased of its stub-shaft. Unless this particular unit has suffered undue ware at this axle, it appears that Lima rely on good luck that these little cogs will stay where they are needed.

When I purchased the DMU as a "previously owned" model, I had the shop owner allow me a longish test run on his test track, because I was aware that these Lima, pancake motorised models had a poor reputation, both for slow running and in lacking pulling power. In fact I was quite impressed by this test, mainly because the speed range was impressive and the slow speed running was nice and smooth. Hence my purchase!

Whether or not the previous owner had suffered this cog-wheel loss problem, whether or not he had caused the problem, I'll never know. Nor will I ever know if that's why he decided to sell; what I do know is that with the drive train built as I now had it, those little gear wheels were very, very likely to fall off. I needed to think up how the problem could be eradicated!

I've included two pictures in the hope of making this discourse easier to understand. The cocktail stick is meant to indicate one of the problem cogs, the point of the stick is actually between two teeth of the cog which is otherwise totally hidden by the large diameter cog above. This latter has a hexagon headed retaining screw as does the similar sized cog to its right. It would appear that all other cogs have no means of retention other than rubbing against these large ones, or another immediate neighbour so retained.

Unfortunately I found that the distance between the face of the small, final drive cogs and the rear face of the large ones was greater than the depth of the small, recalcitrant wheel. Thus, if the small cog ran up its own shaft, it could come out of mesh, but there was also the possibility for it to fall off, - which it had done for me in this running session.

The thinking period was much longer than the time taken to make the modification. My original idea was to drill and tap the gear's stub-shaft end and fit a retaining screw, -similar to the Lima method on the large cogs.

However the stub-shaft is less than 3mm diameter so to leave a safe amount of shaft diameter , 14BA was about as large as would be safe, and at that size I would need to make large headed, special screws. A daunting task.

A much easier method, but perhaps falling into the realms of bodging, was chosen.

I removed the large wheels, centre popped the stub shaft by eye and scriber, and drilled 0.5mm about 3mm deep. A touch of super-glue gel on the end of 0.45 phosphor-bronze wire and wire into hole. After the curing time the wire trimmed to about 4mm length, the stub-shaft coated quite liberally with silicon grease, cog back in position and p-b wire bent gently to about 30 degrees. if the cog now reaches the end of its shaft the wire will not allow sufficient travel for gear meshing to be lost. The p-b wire end can just be seen in the picture

I'm hoping this is a long term solution and that my model railway operating will not emulate BR's early DMU operating problems: i.e. too many and frequent break-downs!!

Better luck with your modelling,
Dave