5"g Simplex steam loco build (hopefully)

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Yup - it should just crack the port open at each end in mid-gear. That is your 'lead', the amount of port opening at dead centres, whatever the position of the reversing lever. With Walschearts gear the direct motion from the crosshead via the anchor link and combination lever provides the lap and lead motion.

Just to confuse you a bit more, if the engine were a piston-valve job, with the 'inside admission' normal for that type of valve, the connections at the top of the combination lever are reversed so that the valve moves in the same direction as the piston, instead of the opposite way.

I don't qualify as young.
I did not think you were young,just my tongue in cheek humour
From what i have read in your posts you seem to have the wisdom of Solomon
Glad to hear i am on the right track,please keep watching me. Tell me are you mostly theory or have you made a few of these beautiful machines
Hi Bamak,

Jumping in and starting to turn the wheels by hand will teach you more than you realize. Obviously, the steam must push the piston when the crank pin is the correct position relative to the wheels. Adjusting one part or another and then carefully observing the results will also teach you what is going on. The more I did this, the less I needed any written instructions on valve timing.

Also, getting air to the steam chests and listening can be helpful as you listen for four equal exhaust beats.

Fortunately, locomotives are, in general, very forgiving. Even before I optimized my valve gear, it work pretty well. The most poorly adjusted valve gear will usually still work and get the job done. I'm sure yours will be just fine and probably work quite well.

Yes, overall position of everything looks good so far. The expansion link looks like it may be tipped forward a bit for mid-gear, this may be due to the eccentric rod not adjusted for length just yet.

Is there much lead when you move the reverser all the way forward or aft? Perhaps its too early to make this a fair test.

Good work on the machine work on the saddle. I had to make mine 1/4" narrower due to having to re-gauge my loco to 4-3/4". I machined the radius using a boring bar between centers on the lathe, a boring head works just fine as you have done.

Tell me are you mostly theory or have you made a few of these beautiful machines

I have been playing with steam engines since I was given a Mamod engine at the age of seven, and have had a workshop and lathe since my teens. I have a degree in mechanical engineering and am now retired.

Most of what I have made seems to be tools, including a lot of George Thomas stuff, and I am a slow worker anyway. I have a box under the bench with almost complete wheels and cylinders for a Simplex which have not been touched since I decided the second pair of frames was also scrap, about 40 years ago. I also made the reversing screw, and nut, for which I made a 1/4" x 20 tpi, left-hand, square-thread tap. I said I make tools.

The most recently completed major tooling project was a camshaft grinder for the ET Westbury Seagull petrol engine that I have bored this forum with on numerous previous occasions. The write-up is way behind, but I have put a recent shot showing most of it at the bottom of: http://www.charleslamont.me.uk/Seagull/ignition.html

Most of the work I have done on steam locomotives has been at 12 inches to the foot, including a taking major part in this ongoing project: http://www.catchmewhocan.org.uk/
Thank you Charles for your info,catch me if you can looks very interesting
The ornate balustrade looks good.The last few years of my working life was designing steel stairs and balustrading.
Thank you for tour input Dave.Yes my thoughts were to build and disassemble etc until the working become clearer
I have repeated the process for full F and full rev,making mods etc and improving and tight spots. Everything looks ok and the ports are covered and uncovered at approx the right time so i am happy for now knowing things are near enough until i can run with air.I am now repeating the process with the farside with a long list of thinks to do and look out for. time 06.jpg

time 07.jpg

time 08.jpg

time 10.JPG

time 11.jpg

time 12.JPG
It really is starting to look like a loco now. The speed at which your building is more than impressive. I'd be struggling with the frames still, but that's just me.
Hi Barry,

Hopefully, attached is the drawing of the eccentric rod for the Super Simplex. As you can see, the center to center distance is something to be determined as the valve gear is set. The Simplex was drawn in 1967 and the Super Simplex was drawn in 1989. Martin Evans learned that you could not exactly specify the eccentric rod length.


14-639 - Eccentric Rod.jpg
Thank you David.3.822" is a long way from 3.9375" as specified on my drg
I am no where near running on air yet and if the eccentric rod centres are critical and are best determined when fine tuning the valve settings then i
will have to make another temp/adjustable rod and have one on each side
until i can run on air. There is too much work in the actual rods to be wasted
I assumed this was the case from what you had done and i am pleased you have confirmed it. Onwards and upwards. Regards barry
Hi Barry,

Yes, I certainly did not want to make the eccentric rods twice, which is one reason (as you have guessed correctly!) for waiting so long to make the final version of them. Running with adjustable rods is nothing to be ashamed of. I did it for months at my club track under full steam! My center to center was even a bit longer than specified by the "estimated" dimension on the Super Simplex drawing.

By the way, a "quicker" way to make the eccentric rods, is to silver solder a 1/4" piece of steel onto the 1/8" thick rod to help form the forked end. This way, you don't have to make the entire rod from "the solid". (What a pain!)

The different center to center dimension between the Simplex and the Super Simplex is not really the point I was trying to make. No doubt, they are different between the two models, because Martin Evans changed the position of the weight shaft on the Super in reference to the expansion link trunnions.

The important detail to notice, was the "*Check on job" message that Martin put on the drawing, with the understanding that this distance needs to be determined by what is needed, not what the dimension is on the drawing. The "check on job" note, is not on the old 1967 Simplex drawings.

Keep up the good work!

After a couple of days in the 90s i have made and assembled the motion to the far side.All turns over well and with valves at both sides the timing makes your head spin. Thanks to help and info from David and Charles.I followed Davids advice and made a second temp/adjustable eccentric rod to get everything somewhere near.As i understand it the valve travel should be .560" in F and rev and about .25" in mid gear
I took the following readings of the valve travel
Nearside is .530" in F and .550" in R Midgear is .260" so somewhere near
Farside is .430" in F and .370" in R with midgear .240" so needs adjusting
When the weather cools down i can start playing about.Its set to hit 100oF
today which means 120 in my shed.
Inbetween the motions i have started to play about with exhaust conns
As David pointed out the screwed fixings originally designed cause problems with assy and he showed me his version of the redesigned bolted conns
I had already tapped the cylinders 1/4" bsp (.518") so thought i would try and incorporate comm screwed/compression fittings.The smallest i could get was 3/8"bsp to 1/2" copper so will try to machine these down to fit,if not
successful then i will think again before also doing the inlet to suit a compressed air conn.All i have now i think is to make and fit the cap glands
to fit the steam chest and reduce in length and finish the vave spindles
Meanwhile its turn the aircon on and pick up a book.NOT Martin Evansexh 01.JPG

exh 02.jpg
Hi Barry,

I will have to see how your fittings will be assembled. It is not clear how everything will be screwed together. If you were to ever need to remove a cylinder, or steam chest, I'm not sure how it would be done. I will follow along and see what you have in mind.

I made my connections from 1/2" copper tube silver soldered into a Y shape, and flanges silver soldered on the ends of each side. The screws go through the flanges and into the cylinder castings. The screws are removable from the inside, as I have has to do this many times!

I think I have sent this photo before, but attached is a shot of my steam supply and exhaust piping. All joints are silver soldered.


DSCN0956 - reduced 4.jpg
Well the temp has been around 100o F for a few days.Too hot to work
but i managed to get in a couple of hours.Not the weather for heavy thinking
on the valve timing so decided to carry on with my idea for the exhaust
Machined down 2 fittings to screw into the cylinder and pass thru the frames
These can stay assembled to the cylinder.Using the last of my silver solder
i partially finished the steam pipes.I am not happy with my workmanship
so if it all works i may remake at a later date.Trying to modify std comm.
fittings was not really worth the effort.It may be better to make everything
again including the compression fittings.The last 10" of my silver solder has been in my tool box for many years so have ordered 2 sticks at $20 eachIMG_2487.jpg




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Hi Barry,

That should work okay as long as you are able to get a wrench onto the compression nut with everything else in place. Are you going to do the steam supply in a similar manner?

Hi David,the male part stays on the cylinder and can be drawn thru the frame
the female should be easily accessable for a spanner. I can however reduce the size slightly or make new small ones.Havent fully planned everything yet
if you follow any of my threads,like the model shaper you will see its fly by the seat of your pants.The inlet is smaller,1/8" bsp not 1/4" bsp and the supply can probably be reduced in size for both comp. air and steam.If comm fittings are too difficult to obtain or access
is difficult then i can make smaller unions.The basic principle of 2 fixed male parts and 2 comp. fittings can still apply.Rain has arrived and the weather cooled down so may get stuck in to valve timing
Hi Baz. Brighton steel used to sell 45% sticks for around $12 Not sure if that's still the case but could be worth a call
Weather has cooled down to the low 20oc so spent a few hours in the shed
playing about with the valve timing,finding tight spots,disassemble and rectify,refit etc.Turns over well with one tight spot (coupling rods i think)
Drilled and tapped the steam chests,made and fitted the 2 cap glands
Finished the valve spindles etc etc Also tacked the exhaust together and
fitted removed etc.Works well but will probably remake a bit more compct
and better workmanship I need to look at the inlet next IMG_2492.JPG



Hi Barry,

Looks good! I now understand how your exhaust and steam pipes will assemble. Should work just fine. The fitting that screws into the side of the cylinder may eventually need some sort of high temp sealer on the threads. Is this a straight thread, or, tapered like a pipe thread?

Hi Barry,

As promised, here are the drawings of the axle pump that goes into the Super Simplex. I do not know if it will fit into the same space for the Simplex. I do not seem to be able to attach photos to PMs.


Axle Pump Detail - 1.jpg

Axle Pump Detail - 2.jpg
Thanks Herbie,but brighton no longer sell silver solder
Thanks David,the bsp threads are parallel and if needed will use teflon tape
The feed pump details are the same as my drg but i also have an additional
drg 6a showing a double acting pump.Will stick with this one,did you build it up or is there a casting ?
I was not happy with comm flare/olive comp fitting to copper so thought i would try something different for the inlet using the ngarden water hose
sealing method.I bought a 1/4" bsp T and made the rest of the fittings from brass.Works well and more compact will look at redoing the exhaust
Made a start on the hooks just for looks but cant understand why the 8x5mm
section is 13/16" long to go thru the 5 thk beam.Is it just a nut on the back
with free movement or is it spring loaded.I dont have any details
Also giving thoughts to the smokebox and 5" dia tube is unavailable here
in mild steel or brass.May have to use 140mm dia and try to spring it down
Did it often many years ago not difficult with youth,oxy/acet etc,but now ?
No choice will have to give it a go or machine from solidHook 01.JPG

inlet 01.JPG

inlet 02.jpg

inlet 03.jpg

inlet 04.jpg
Hi Barry,

Straight threads on the steam pipes, hmmm... This will be a potential leak point if there is no shoulder to screw against. The lock nut shown on the drawing will help prevent leak when installed with a little thread sealer. It looks like your steam supply pipe will include a lock nut. Perhaps the exhaust pipe will not be a problem.

The smoke box is usually rolled and then silver soldered. It's typically made from brass, steel will rust pretty badly on the inside in this application. The inside of the smoke box is turned to fit the boiler, or an adapter ring can be machined to fit the smoke box to the boiler.

My axle pump was made from a bronze casting, but, you can easily make it from a solid block. I have made the hand pump from the solid as it is almost made exactly like the axle pump. The axle pump I have shown actually is double acting. Or, more precisely, 1-1/2 acting! The pump delivers when moving the ram in both directions. Just a little less in one direction than the other.

On the steam supply pipe, don't forget to include a place to mount the steam oil check valve at the bottom of the T. You don't have to make the valve yet, just a threaded hole that it can screw flat into when you are ready. Meanwhile, you can just make a threaded plug to screw into the hole. Perhaps you can silver solder something onto the bottom of your T to fit the steam check valve on. Might have been easier to just start with a block of copper or bronze as shown in the drawing.


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