John Cutler
This turned out to be a prolonged job!
The Terrier splashers need to be widened carefully. I managed to stop filing just in time, although a scratch is visible on the front splashers. A P4 conversion will be tight. Filing out the splashers exposes the metal footplate (which is hard going!); this needs to be insulated from the widened wheels. I covered with a thin layer of acrylic paint but thin sellotape cut to shape might be better.
Alan Gibson’s wheels for the Terrier gave me more trouble than usual. The holes for the crankpin are not ready moulded or drilled. A very faint depression marks the crankpin location. It is very easy to drill off location and one wheel duly fell victim. I used a long crankpin bearing to try and keep the (0.7mm) drill vertical and this worked surprisingly well. Having drilled through, I made a thread by screwing a crankpin from the front of the wheel, followed by a 2.3mm countersink of the hole at the rear of the wheel to allow the crankpin screw to seat. The screw was secured with a spot of superglue before tightening into place.
The gear from the Hornby wheels needs to be reused. This should be knocked or squeezed out of the Hornby axle, not twisted out. The Gibson axles should be prepared; I recommend smoothing out the chamfer on the axle ends and using fine wet-and-dry abrasive paper to try and eliminate any possible sharp edges on the ends. The Gibson axle for the drive needs to be carefully marked out for the position of the gear wheel. There is very little room for error; clearances are tight. Measure everything up with spacing washers in place on the chassis. The rear driving axle needs to be a fairly tight (but running) fit with no side play so the new gear wheel cannot foul. I abraded the gear wheel position with a file rolled across the axle but did not apply any glue (as an extra safeguard) until I was 100% happy with the final gear wheel location. Remember to slide the gear onto (and off) the axle; do not twist.
The rear driving axle should therefore have little side play. It is desirable to minimise the sideplay on the front wheels as well; this minimises the filing of splashers required. I used 2x 1mm and 1x 0.5mm EMGS washers each side for these axles. Note these gave 2.8 mm of washer each side; the washers are each 0.1mm overthick according to my vernier. Do not just accept the product descriptions, measure these things yourself! The centre axle needs sideplay to allow transit through curves; I used 2x1mm washers each side. Note I aim for a Back-to-Back in the range of 16.5mm to 16.7mm.
I used a GW wheel press to quarter and press the wheels onto the axles.
Unfortunately I failed to prepare the wheels sufficiently and ended up applying too much pressure. The result was an unacceptably wonky set of wobbly wheels. From experience there is no point in trying to rectify this so all were scrapped and a new set purchased. The second time I spent more time smoothing the axle ends and put a tiny countersink on the wheel face with a 3.5 mm drill. Someone (the original Mr Alan Gibson?) in the distant past recommended wetting the axle ends with spit to help. This worked but there is still a small amount of wobble and I pray for the day wheels with stub axles or similar are produced.
The 1/8” axles are reasonably free-running in the mazak (?) chassis and I applied a spot of clock oil to each bearing point. Maybe Teflon grease would be better? Fortunately the brake blocks need no adjustment; clearances are OK. The Hornby coupling rods can be re-used and are a surprisingly good fit on the Gibson crankpin bearings.
I was not at all happy with the Hornby pick-ups. Out-of-the-box running on OO track was jerky and even after adjustments to the pick-ups, was not smooth.
There was no way pick up from the centre axle was going to be reliable given the wider EM back-to-back and sideplay. So a piece of 0.4mm PCB was wedged between the centre springs under the keeper plate. This was soldered to the bent-back central pick-ups and 0.3mm phosphor bronze wipers formed to lightly rest against the wheel flanges.
The result is acceptable but I cannot help feeling Hornby missed a couple of tricks in not having a heavier body and not having a spring on the centre axle. I attached extra weights in spaces in the side tanks and also in the screw holes. But this only adds a few grams. I used Blu-Tak as a semi-permanent adhesive. I had a bad experience of a warped smoke box resulting from gluing lead weights with epoxy tightly fitted in an old Terrier plastic boiler; I now prefer something less rigid!
I would not recommend a conversion to P4. There is no vertical movement in the axles; effectively this is a rigid chassis. Moreover I would be scared of the clearance needed in the front splasher. I guess one could fit a Branchlines chassis but the lightweight body and resulting lack of tractive weight is likely to be a problem.