By Mark Hamlin
My Maxitrak Sapphire entered service a little over 2 years ago, mostly running up and down the garden but occasionally venturing out into the big brave world of the club tracks at Harlington, Ickenham and Harrow.
She is fitted with disc wheels (the significance of this fact will be revealed later) and an injector (hardly ever used it, the crosshead pump has proven more than adequate for the job)! I specified the Walschearts valve gear option (more ‘gubbins’ for the kids to look at when she is running) and brakes (useful for holding the train stationary when loading on the portable track but I usually forget to release them and then wonder why the train’s not moving).
Although very pleased with her performance, especially as I’ve grown more confident with her, there were a number of things that I felt could be done to improve her. These modifications would apply equally well to any of the other smaller steam locos.
Walschearts Valve Gear
Timing kept going out due to the return crank slipping on the end of the crank pin. This was rectified by replacing the slotted head machine screw, that is supposed to clamp the return crank, with a 6BA (I think) hex headed bolt which screws right through the crank allowing a lock nut to be attached to the other end. The use of a hex headed bolt also means you can adjust the valve timing much more easily as you don’t need to have the return crank positioned so that you can get at it with a screwdriver.
I also felt that reliance on the lifting links to provide lateral alignment for the weighshaft was a little crude, so I machined 2 grub screwed collars to hold the weighshaft between the frames. I don’t know whether this has had any real benefit but I suspect it might help to reduce wear in the valve gear linkages.
The single grub screw on the top of each arm, that is supposed to secure the arms to the cross-shaft at the rear of the chassis, proved woefully inadequate to transfer any real braking force from the brake handle. Furthermore it is almost impossible to tighten these grub screws due to their proximity to the footplate above. Drilling and tapping 2 new holes in the sides of the arms has made life easier and with two flats filed into the cross-shaft, the brakes now work. However, I might yet go for the semi-permanent solution of drilling through the arms and shaft and using a roll pin to lock them solid!
I felt that the thermal efficiency of the design could be improved by lagging the boiler and steam pipe. As I didn’t want to modify the saddle tank I retained a single sheet of cork as the insulant but wrapped right around the boiler and firebox and held in place by a tinplate cladding sheet secured by new longer boiler bands.
The string and Polyfilla lagging for the steam pipe is not my idea but came from Brian Watt (Spring 1999 issue of ‘Road n’ Rail’); very many thanks for your help! Just one thing though; I was in a hurry to get it done before the next weekend running session and tried to do it without removing the cab. Not a good idea as I’m sure I took longer threading the string round the inside of the bunker than I saved by not removing the cab!
I didn’t really like the idea of securing the smokebox door with a grub screw in the side so used a technique first shown to me by Harry Lumb of the Westland Club in Yeovil, some years ago. He secured the door of his Don Young Rail Motor with a socket head cap (Allen) screw. A 10mm square steel bar is held across the centre of the smokebox by two blocks screwed to the inside, as shown below.
The door can then be tightened up with an Allen key to give a really good seal especially if a drop of steam oil is placed around the rim of the door. But don’t forget to seal the original hole by putting the old grub screw back into it; I did forget and couldn’t work out why the loco wouldn’t steam for toffee.
I filled the dummy bunkers with lead and then Araldited some lumps of anthracite on top; looks the part and adds some useful extra adhesive weight.
Sapphire’s first public running session was on my portable track at our church fete and after about an hour of running a hot spark was ejected from the chimney landing on a small child. Much complaining from irate parents, and a reversion to ‘Simplicity’ power for remainder of afternoon!
I then made up a spark deflector (using brass sheet and a 1” spring clip to secure it to the chimney) and Elsie ran around the Harlington track, nicely showering sparks to right and left. Irate visitor approaches and complains that a spark has just burnt a hole in her pram cover! A new spark deflector was made to eject sparks to the left only (away from public at Harlington) and we set forth again, this time in the garden. Daughter sitting on carriage behind me suddenly yells “Dad the garden’s on fire” and we race for the hosepipe to extinguish the straw that my wife had just put round the strawberry plants to keep them warm! Something definitely needed to be done to tame this mobile flame-thrower.
Firstly I tried reducing the blast up the chimney by increasing the diameter of the blast nozzle from the original 5mm eventually up to 6mm, carefully keeping a spare in reserve in case I went too far. Then I bored out the chimney to give a 1° internal taper and fitted a petticoat pipe in the bottom of the chimney. This all seemed to help but we still seem to fill the smokebox with ash after an hour or so of hard working, after which the steaming rate goes down and the spark ejection rate goes up!
I contemplated the Welsh narrow gauge solution (oil) but decided that gas was probably a simpler option. So I bought a Burrell burner from Maxitrak, made up a new ashpan to hold it and strapped a 3.9Kg Propane cylinder to the driving trolley. I figured that this solution might just be sufficient for portable track use where the boiler could be mortgaged during each run and then recovered whilst reloading with new passengers. However, as predicted by Andy Probyn, the Burrell burner just isn’t sufficient and I found that I couldn’t get more than 50 psi on the clock and then only after about 10 minutes recovery time. Productivity would have been diabolical on a portable track so that plan had to be abandoned. Anyone want to buy a spare Burrell burner?
Securing the Rear Axle
Whilst trundling past the steaming bays at Ickenham several members were noted looking intently at Sapphire’s back wheels; sinking feeling in pit of stomach! Someone called out that the rear axle was moving! One of the rear axle securing bolts had come loose AGAIN!
I decided to make up a pair of angle iron supports to secure the axle blocks to the frames like a pair of inverted hornguides. These were bolted to the frames using two 4BA bolts each, with the tapping holes for the bolts being carefully drilled using a hand held electric drill passing through one of the holes in the disc wheels. The brakes came in handy here to stop the wheels from moving during the drilling process. The reason for using 4 BA bolts was that these have a very convenient tapping drill size of 3mm. Also the 4 BA box spanner that I had in my toolbox was just small enough to fit through the holes in the disc wheels to screw the bolts in. Final tightening can be achieved with a thin open-ended BA spanner passed between the back face of the wheel and the frame.
This solution has the additional advantage of increasing the rigidity of the frames at a point of potential weakness where they are cut away for the rear axle to pass through, and yet doesn’t prevent the small amount of vertical movement that the rubber blocks are supposed to provide.
Whilst these various solutions are not particularly elegant they have proven to be effective and, with the exception of the abortive gas burner, haven’t involved any materials that weren’t in the scrap box. I hope these ideas may help other members to improve their locomotives.