Specific Changes & Modifications

What I will attempt to do on this page, is to document item by item, what I changed or modified. Remember, this is a freelance locomotive, not a scale model. It can be built in any way that suites the builder.  The order of the items will roughly be in order of things as they appeared in the Model Engineer buildarticles.


The frames are pretty straight forward. The biggest complaint I have, is that nothing is really identified. There are an overwhelming number of holes in the frames, especially for a first time locomotive builder. What are all of these holes for? So the first thing I added to the frame drawing, was to label what each and every hole is for. Before I could label anything, I had to read all of the articles and figure what went where and what it was called. The oblong holes at the left end of the frames are for the steam pipes that go in and out from the cylinders. I made these holes rectangular so my flanged fitting would work. I made the flanges large  enough so I could use 4 screws on the steam pipe flanges instead of the 2 as drawn. 
After figuring out what all of the holes were for, I discovered that most of the "patterns" of holes in the frames are for bolts to pass through. I only drilled these holes with the tap size drill. Then, when the frames were separated, the part to be fastened was clamped to the frame and matched drilled with the tap drill. The tap drill size hole in the frame was used as the drill guide. Then the parts were separated and the tap drill size hole in the frame was opened up to a clearance size hole for the bolt. This method assures good alignment of the holes in the frame and the parts attached to it. This method can be used many places in this build, not just the frames.
The 3/16" reamed hole near the motion plate angle brackets is for aligning the expansion link brackets and motion plate assemblty. A rod is passed through this hole and through the brackets. This positions the entire motion bracket assembly correctly in respect to the cylinders. This is not mentioned anywhere in the building text, but, it is in the first set of articles for the regular Simplex.
The large 7/8" hole is for blow down valve from the boiler to pass through. I do not recommend opening this hole until the boiler can be mounted. Then, transfer to the frames, by measurement, the position of each of the blow down bushings. This will assure the blow down valves are in the center of the holes in the frames.
If you are re-gauging the locomotive for 4-3/4" track, the 4-1/8" dimension on the three frame spreaders should be changed to 3-7/8". Also, the 4-1/8" dimension on the front and rear buffer beam should be changed to 3-7/8".

Axle Boxes

The radius on the axle box flanges, I cut on a rotary table. The radius I used is 4-1/8". It is not critical, but, this seems to work okay to let the axle boxes go up and down independent of each other. The reduced flange note, is so the axles have a bit of side to side play. The most being in the rear axle, and the least in the forward axle. I also bored the axle boxes large enough to take a bronze sleeve. I put the oil reservoir in the center top and drilled small holes to get oil to each side as well as straight down to the the axle.

Horn Stays

The horn stays I simplified a bit. I simply made a thinned area where they fasten to the horn blocks instead of a notched area. The holes in the horn stays must provide plenty of clearance for the spring pins, they must not touch when the axles go up and down.


On the axles, the 4-11/16" dimension should be changed to 4-7/16" for the re-gauged dimension. This will make the over all dimension 5-13/16". If you use a rotary table or index head to quarter the keyways, you will want to make the over all length longer, to allow for material to go into the chuck.  I made my over all length 7", and after machining the keyways, cut the extra off.


Cylinders - Make sure when drilling for the studs that hold the steam chest to the cylinder, that you avoid drilling into the steam ports that go to  the cylinder ends, and also avoid the hole in the steam chest that the valve spindle goes through and the space for the packing nut. Also avoid drilling into the steam inlet hole in the steam chest. Layout and drill the holes for the studs last, to ensure there are no collisions!
Also, as mentioned earlier the cylinder was decreased from 1-9/16" to 1-3/8".


For the crosshead, I used 4 screws from each side to hold everything together. The screws on the inside are flat head and countersunk, and the ones on the outside are hexagon socket screws. The offset for the drop arm is a separate plate that is held in place by the same screws that hold the cross head together. I used taper pins to hold the piston rod to the cross head, two on each side, #4/0 by 1/2" long.

Motion Plate

The motion plate has an actual dimensional error. The 2-11/16" dimension should be 2-5/8". Also, if you use laser cut plates, these may have errors. I had to mount mine 1/16" below the edge of the frame to work correctly. The small unidentified notch in the corner of the motion plate is clearance for the valance.

Expansion Link

If you use laser cut plates for the expansion link, the plates are a bit thicker than required. I thinned the outer plates so the finished thickness of the expansion link is 9/16". If it is thicker, it will not fit properly between the trunnion brackets.

Reach Rod

I made the reach rod for the reversing gear with the offset on only one side. With the frames moved closer together due to re-gauging, this was possible. 

Water Gauge

For the water gauge fitting, I used the drawing for the regular Simplex, but, I made the blow down valve fully captured so it would not unscrew from the fitting. The Super Simplex drawings do not provide any water gauge. Also, the top feed for the glass from the boiler, needed to be longer than as drawn.

Draughting in the Smokebox

In the smoke box, the distance from the choke to the top of the blast pipe is drawn as 2-3/16". This should be changed to 1-11/16", bringing the blast pipe 1/2" closer to the choke. To do this, just make the blast pipe longer. The overall length of the smoke stack pipe is 3-3/4". A 2 degree taper on the side will put the choke about the right place.

Blower Jets

I installed the jets into the blower ring at about 5 degrees instead of the 3 degrees as drawn. This is because the blast pipe is closer to the choke.

Blower Smokebox Tubeplate Connection

The blower connection for the smokebox tubeplate, has several threaded areas. For the internal thread I used a 1/4"-40 model taper pipe thread. I put the same thread on the hollow stay that screws into this fitting. This is a difficult assembly, and the idea is that this connection does not leak. Using tapered threads helps in this direction, with the addition of some very high temperature thread locker. This is screwed together after the boiler is finished.

Regulator Tube O Ring Seal to Wet Header

When using an "O" ring to seal the connection between Bush "A" and the wet header bush, I needed to have 1/8" between the end of the wet header bush and the counterbore in bush "A", in order to get the proper compression on the O ring. I have no extra washers or gaskets here, and it all seals perfectly. You may have to experiment depending on your O ring.

Safety Valves

The safety valves are a Gordon Smith design instead of the one provided on the drawings. The Smith ones are very nice. The springs, balls and drawings are available from Polly Engineering. All quite inexpensive and not too hard to make yourself.

Ashpan and Grate

The ashpan I made pretty much to the drawing, except I did add a few more holes around the edge of the pan for better draught. I also lowered the center of the back part of the pan to allow a little more ash to accumulate before having to dump it. I also made a slide out door on the bottom of the pan to empty the main part of the pan with out having to dump the fire. It is all stainless steel. silver soldered together. The grate is a commercial product available from Blackgates. You have to cut it to size and form it for the sloping shape.

Backhead Layout

I changed a few things on the backhead. The fire door opens to the left because I was not sure how I was going to get my fingers onto the handle to open door if it opened to the right. The handle would be tucked right under the water glass blow down valve. All the screws for the fire hole door hinge and latch go into blind threaded bushings silver soldered into the backhead.

Injector Water Valve

I installed the injector water valve onto the inside of the right hand frame in the cab. The drawings show it mounted on the back water tank, but, I have decided to not have this tank. My tender/riding car provides plenty of water in combination with the side tanks.

Injector Steam Valve

This valve is not identified in the build articles. It is on page 36 of the July issue near the bottom of the page. There is a valve, with no identifying label. It is the injector steam valve.

Blower Valve

Also, near the injector valve, is a valve labeled "Blower Valve", this is incorrect. This should be labeled, "By Pass Valve".

Emergency Hand Pump

This I made from a solid block of brass. I initially made the axle pump with stainless balls. I did not always get a good seal with the metal balls. I switched to Viton balls, and have never had any problems. I also did this with the check valves to the top feed of the boiler. Viton has no problem with the high temperature steam. I also moved the output connector from the hand pump at the other end. You can see in the photo section exactly what I have done. I also added a packing nut to the piston rod on the hand pump.

Whistle Valve

I used a whistle valve that appeared in a past issue of Model Engineer. It uses a large disk type valve instead of the typical rod that pushes on a little ball. The disc type valve will pass much more steam than the rod and ball type. If anyone wants detail for this valve, let me know and I can help you out.