56XX chassis repairs in P4
A few years ago, I was fortunate enough to buy a Mainline 56XX at a show, that had been converted to P4 by a well-known professional modelmaker, from the man himself. The loco features a scratchbuilt chassis (with single rocker compensation), Ultrascale wheels and a Portescap motor.
When I first bought it, it ran really smoothly. The chassis needed a little paint re-touching and the body has been waiting for a few additional details, but it is essentially a nice and useful loco.
When I last ran it, prior to the current lockdown on Re6/6's Marsh Sidings layout, I noticed that it had developed a slight hesitation, so I put it to one side, intending to investigate and hopefully rectify the problem.
Having looked at it recently, the hesitation was still there, albeit only in reverse direction.
I decided to give it a spell on the rolling road, but that made matters significantly worse.
It was time to dismantle the chassis and find out exactly what had happened.
Well, the nature of the problem soon became evident, although dismantling the chassis turned out to be a little harder than I had anticipated.
The problem was due to the amount of lubrication (applied by the previous owner) had evidently managed to affect the grip that the Ultrascale driving wheels had on the axles, as the driven set of drivers appeared to have gone out of quarter.
The loco is driven on the rear axle and I wanted to drop the leading and middle drivers out, for cleaning and inspection. To do this, I wanted to remove the coupling rods, but turned out to be a bit more challenging. Ultrascale use a round nut to secure the rods, which had evidently been glued in position on the 14BA thread of the crankpin. Each time I gripped the round nut in a pair of pliers and turned, the whole crankpin turned with it.
Eventually, the driving wheel that had gone out of quarter, just fell off the axle! At least that made it easier to get at the screw head for the crankpins behind the driving wheels.
I subsequently managed to get the remaining rods from the other wheels off, although a driving wheel from the leading wheel set also came loose.
I think I am going to have to completely re-secure and re-quarter the lot, before I re-assemble the chassis.
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