No.57 DMusings
Following on from my last Post I have been running playing
with my DMUs
When I want to watch trains ‘go by’ I can operate the Main
Line as a continuous loop with up to three different trains following each
around all at the same time. The power
comes from four different Gaugemaster DS controllers which is kept constant for
all trains. This does have the
disadvantage that if one train runs faster than the others it will catch one of
the other trains up. Not to worry it is
relatively easy to find a rail section and let it have a rest. Similarly if one of the trains is
significantly slower, then the other two trains will have to have a rest!
I was attempting to run all three Bachmann DMUs, Class 105,
Class 108 and Derby Lightweight. It was
very obvious that the Class 108 was lagging – why? On first inspection there did not appear to
be anything seriously amiss. However I
did note that the PCB was dated 2006 showing that the unit was seven years
old. On further inspection I was
concerned about the gluey grease around the worm drive and gearing. To cut a long story short I cleaned the
grease off with methylated spirits, reapplied some sewing machine oil, and made
an instant improvement in performance.
Body fixing screw
First the single body fixing screw needs to be unscrewed –
this is easier to do with the front bogie removed.
Getting inside the Bachmann Class 108 is a similar exercise
to that on their Blue Pullman. There are four
tabs on each side sticking out from the seating unit and rear metal motor
enclosure. In my case working from the front
of the unit I was able to lever the body shell away from the chassis with my
finger nails – if you have less confidence you might need to adopt the
technique I used for the Blue Pullman and slide in a piece of stiff paper.
With body shell removed the single motor bogie fixing screw
can be undone – allowing the motor bogie itself to drop out. There is no need to remove the four screws on
the metal motor housing unless you are wanting to inspect the motor and perhaps
drop a spot of oil on the main motor bearing.
The view above shows the main parts cleaned of grease. You will need to take care not to lose the small
nylon washer that Bachmann have used between the brass worm and brass thrust
bearing.
Another view, this time with the worm drive back in place and
waiting for the cover to be fitted (a clip fit).
Refitting motor bogie
Getting the motor bogie back into the recess in the PCB
requires a little bit of care (and perhaps confidence). Once ‘inside’ the unit there is sufficient
space to allow the bogie and driving spigot to be lined up and pushed into the
matching recess in the motor. At the
same time the top of the bogie has to be lined up with the hole in the top of
the metal motor housing and the fixing screw fastened. Finally the body shell and chassis are
matched together not forgetting to replace the body fixing screw under the
front bogie.
Finally a view of the reassembled unit. From a quick inspection of my other Bachmann
DMUs, they all seem to be assembled in a similar fashion. The only significant difference that I noted
was that the motor in the Derby Lightweight unit is hard wired to the PCB. I did wonder if this perhaps accounted for
its noisier operation, some vibration from the motor being transmitted directly to
the body shell?
The performance of my elderly Class 108s is now midway
between the Class 105 (Cravens) and the Derby Lightweight. The latter have by far the brightest internal
lighting – so is that where some of the power is being used? One final observation – all my DMUs seem to
perform better with the motor car pushing the trailing car – is that something
about the efficiency of the worm drive and thrust bearing?
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