Well I've just about completed the kit and I'm reasonably pleased despite the shortcomings outlined in my earlier entry.
I tried two new features (for me) on the chassis, CSB suspension and Alan Gibson plunger pickups. The CSB suspension does make life a little more complicated as all hornblocks have to move up and down (not sideways!) and unlike a compensated chassis, the suspension only works when weight, i.e. the body, is applied. I used spring steel wire but even here care is required as the gauge has to be such that it allows deflection, if the wire is too stiff the hornblocks will not move in the vertical plane. One advantage though is that the deflection is minimal. With a compensated chassis the hornblocks move to a far greater extent which can cause problems with the pickups which are at risk of "running off" the tyres.
One point I didn't mention in my earlier entry was the method I use to obtain a working clearance in the hornblocks. I used High Level hornblocks which are already reasonably accurate but will require a little work to obtain a nice sliding fit. Rather than use a file I use fine valve grinding paste on a scrap of nickel silver rubbing the axlebox on it until I get a perfect fit in the hornblock. Of couse it is important to ensure all trace of grinding paste is cleaned away, I use an ethyl alcohol spray obtained from late lamented Maplin's. To ensure I always work on the two sides adjoining the hornblock I scratch "T" (top) on one face of the axlebox.
The photo below shows the chassis after spraying with my usual Halfords Matt Black. The CSB beam, in reality the spring wire, is visible.
The photo also shows the bush for the Alan Gibson plunger pick-ups. I had never used these before so was interested to see how they performed. It is apparent that the 2.5mm hole required can weaken the chassis if the depth is minimal. However it was difficult to see how current collectors could be arranged to bear on the leading wheels.
I sprayed the wheels separately prior to fitting using Maskol to protect the treads and the back upon which the current collectors would bear. Having used the axle jigs to ensure the axleboxe centres were exactly the same as the coupling rods I expected little difficulty in getting the chassis to run freely. Not the case! I spent a long time moving the wheels imperceptibly to get the quartering correct and also enlarged the holes in the coupling rods slightly. There does need to be a little clearance between the coupling rod and the crankpin bush but too much and the chassis will never run freely. I tried the old trick of lining up the spokes but still spent the best part of two or three evenings trying to elinminate the slight binding that was occurring. One problem may have been that the Ultrascale wheels are not as tight on the axles as Gibsons. This makes them a little easier to fit but the downside is that they move too easily. Eventually when I did get the chassis running smoothly I applied a little Superglue to the axle ends to fix them permanently.
Next issue was offering up the chassis to the body. For some reason the 1624 motor was now too long and protruded well into the cab. The Gods weren't smiling on me after all. I obtianed a 1620 from High Level and after some sweating trying to remove the worm from the 1624, managed to fit it to the 1620. The new High Level gearboxes are an improvement on the already excellent earlier ones but from past experience it seems the worms on the new ones are a tighter fit. The plunger pickups were assembled and following my normal practice (if possible) the rear wheel pickups were fitted on top of the chassis, thin phosphor bronze wire soldered to a piece of copper coated paxolin with a small gold plated bead in turn soldered to the end of the wire and bearing on the tread. For the first time I have a GWR tank loco where neither pickups or motor intrude where they shouldn't.
The Alan Gibson plunger pickups worked very well with minimal pressure on the back of the wheels. As they are lightly sprung contact with the back of the tyres is maintained at all time although very thin wire must be used otherwise the operation of the plunger is restricted. I would certainly use them again.
The photo below shows the chassis almost completed but still with the larger motor. The Ultrascale wheels look good, the small hole in the axle ends makes quite a difference.
The outside bearings to the trailing wheel are a separate etching. I fitted these after replacing an ejector pipe I had soldered each side, I found that it fouled the wheels. You will also see that a little touching up is required.
Fitting the completed chassis to the body resulted in further problems as the motor and rear pickups still fouled part of the inner casting of the tank sides even if they didn't protrude into the cab. It wasn't too difficult to remove the offending white metal but what was more of a problem was the clearance between the front driving wheels and the splashers. Whilst manufacturers helpfully provide alteranative frame spacers for EM and P4 the body clearances often become a problem, particularly with white metal kits where of necessity the material has to be thicker. Using a chunky file I managed to remove enough without going through the other side.
Having done all this I tried the chassis and body combination and it worked very well. Unless you have used High Level gearboxes you have no conecption as to how quiet a locomotive will run. The plunger pickups worked impeccably and even my phosphor bronze wire ones at the rear needed no adjusting.
Whilst the body had been substantially completed I decided to replace the etched lamp irons with flattened brass wire soldered not just to the surface of the white metal but I also drilled a hole to fix the wire more permanently. I always feel it is no use having a perfectly detailed model if over time parts drop off. Various scraps of metal were used to make the odd shaped cylinder in front of the right hand cab window and brass wire for the various pipes along the footplate valance. Incidentally if anyone thinks the wire on the valance on the right hand side isn't straight, it's exactly as it was on the prototype, it curved gently near the cab end. I fashioned the various auto fittings on the buffer beam and a brake cylinder to go under the rear buffer beam. These are very prominent on the prototype.
I will be getting the body professionally painted as I feel a decent paint job really lifts a model and it's something way beyond me. Whilst working on the kit it did again make me consder the limitations of 4mm modelling where the smallest parts of a steam locomotive really can't be fashioned with any accuracy. If you want to see what I mean have a look at the 7mm models of 517's on the Lee Marsh models site.
I'm not sure whether my blow by blow account is of interest but I try and detail the way I do things in the hope others might find it useful. If I've learnt by my mistakes so others won't make them in the first place.