Split Gears
on Graham Farish Locomotives
Fred Hempsall
The Problem
The black
plastic gears on some UK made Graham Farish locomotivess have an unfortunate
tendency to split or crack between the metal axle and the root of a gear
tooth. Thus they no longer transmit drive properly and can cause the gear
train to jam or lock up. The earlier white nylon or brass gears do not
suffer from the problem nor, so far, do the stronger fatter ones from
China.
Symptoms
A locomotive
or multiple unit may start to make a noticeable clicking sound, be very
jerky when starting, run very slowly or not at all in one direction, or,
in the case of those mechanisms
with a spring drive in place of a conventional worm, a bogie may lock
and force the end of the spring out of the bogie. In short, any locomotive
or unit which starts to misbehave should be stopped, removed from the
track and checked for split gears.
Which ones split?
Basically the
problem is with the gears in the middle of diesel, electric and multiple
unit driven axles. It also occurs in the smaller intermediate gears in
the bogies and the reduction gears of DMUs. The drive gear on the Jinty
and 57XX tank engines also suffers but otherwise the steam locos seem
to be free from the problem.
How to Check
Remove the
bogies one at a time from the chassis. Roll the uppermost gear with the
ball of a finger for at least one full revolution in each direction. It
should turn without any stickiness, 'grinding', or restriction other than
the normal friction of the gear train. If it doesn't, unclip the bogie
sideframe taking care not to lose the coupling and spring. Remove each
wheelset in turn and attempt to push the gear sideways on the axle. If
it moves the gear is split. If all the wheelsets are OK but the problem
persists then the only thing to do is to remove the intermediate gears
in turn and examine them under a magnifier. Even after finding one gear
with a fault continue checking all the rest on a loco or unit as others
may be 'hiding'.
The Fix
Basically,
replace the offending wheelset or gear. It is possible to remove a wheel
from an axle and fit a replacement gear but it is not easy without specialist
tools and is often not successful. Better to replace the wheelset, preferably
with one having the brass or white nylon gears or one with the new Chinese
made fatter black gears. In general it is wise to replace all the axles
as, if one has failed the others may be about to. It is possible to remove
the gears from the cente axles of the Co-Cos and A1As and refit the now
ungeared axle with very little loss of performance, although it may be
necessary to elongate the axle hole vertically to give it a little more
upward float.
Spares
These are available
from BR Lines, 97 Park Lane, Guisborough, Cleveland TS14 6PA, the approved
service agent
Prevention
Sadly almost
impossible other than by avoiding locos with the UK made thin black plastic
gears. In my experience failures have occured in new models straight from
the box, those that have run many track miles, still others that have
been in storage, and so on. In short there seems to be no way of predicting
when or if it it might happen. Oil has been suggested as a contributory
factor as it could cause the plastic to become more brittle over time,
but here is no conclusive evidence either way. Although the problem mostly
affects UK made stock, the very first imports from China used gears of
the same dimensions which were also susceptible. Happily the new stronger
fatter gears seem to have cured the problem and, of course, the new diesels
are now appearing on a totally different mechanism.
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