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.
Brakes
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!
Lagging
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!
Smokebox Door
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.
Additional Weight
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.
Drafting
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.