Sunday, May 9, 2021

Spring Switches on Tehachapi Pass Exhibit - by DF Willoughby

 I've seen several comments around the internet recently asking about functional HO Scale spring switches.  LMRC club member David Willoughby was good enough to go dig up some photos and write the following document about the La Mesa Model Railroad Club's spring switch installations.

SPRING SWITCHES

on the

TEHACHAPI PASS EXHIBIT

by David Willoughby

Recently, I have received a couple of requests for information about the La Mesa Model Railroad Club's spring switches. First, I'll briefly describe our switch construction methods in general, and the linkage we use for regular switches between the motor and the points.

OUR SWITCHES ("TURNOUTS")


Center Siding Spring Switch at the East end of Bena. - D.F. Willoughby photo

Nearly all of our 750 or so switches (or "turnouts," as model railroaders and railroad civil engineers call them) are hand-laid on wooden ties. Our methods were developed over five decades ago, and were based on an article in Model Railroader around 1955 by author Robert F. Cushman. Initially, all frogs and points were made by hand from suitable nickel-silver rail; usually we now use cast frogs and points, some or all of which are available from Detail West.

One way our switches differ from many other model switches is that there are gaps between the frogs and closure rails so that the points and closure rails can be electrically connected to the adjacent stock rails. This makes the gap between the stock rail and the open point as close to scale as NMRA wheel standards will allow, without running the risk of a short circuit if the back of a wheel brushes against a the point. These days, this characteristic is sometimes called "DCC-friendly" because it minimizes the likelihood of a short circuit that can shut down a DCC booster, stopping every engine in the section it powers.

We use rail joiners on the ends of the closure rails loosely fitted to the heels of the points as a hinge, and connect them to an insulated throw bar using 00-90 screws, which are left loose enough that they don't bind. The throw bar, which is made of 1/16" thick phenolic, rides in the space between two adjacent ties. (These are usually the head-block ties, through SP standards specified the use of only one head-block tie for hand thrown switches.) In the center of the throw bar there is a hole for a piece of .030" dia. steel piano to link it to a switch motor. A hole through the ballast board and roadbed below the throw bar is widened into a slot to allow a wire from the motor linkage below the roadbed to move the points. The first photo attached shows what one of these switches looks; this one is a spring switch at the east end of the center siding at Bena.

"Normal" PFM Switch Motor installation. - D.F. Willoughby photo

Over 35 years ago, we standardized on PFM/Fulgurex switch motors, which were among the first motors available when twin-coil solenoid switch machines were still nearly universal in model railroading. (The PFM motors are no longer generally available in the U.S.) They have a plastic throw bar with holes at either end for a wire to link the points to the motor assembly, and cutoff contacts to stop the motor at the end of its travel. Our standard installation has the motor screwed to a small piece of 3/8" birch plywood with a couple of slots or oversize holes that slip over studs screwed into the bottom of the roadbed. We also put a Molex ® connector on the wires to the motor for motor power, and for the frog and auxiliary contacts. The connector and wing nuts on the studs allow a motor to be swapped out for repairs without any tools or soldering. The oversize holes allow the motor position to be fine-tuned so that the tension on the points is approximately equal in both positions.
To link the motor to the point throw bar, we fabricate a "Z-link assembly" using a piece of 1/32" I.D. brass tuning soldered to a small brass plate that is then screwed to the bottom of the roadbed. A piece of .030" steel piano wire is slipped through the tubing and bent upward at one end and downward at the other, forming a "Z." The lower end goes down into the throw bar in the motor and the upper end extends upward through the hole in the throw bar that connects the points. The second photo attached shows one of these standard installations.

SPRING SWITCHES


The Southern Pacific used spring switches extensively, especially where they could be used in place of a power switch controlled remotely by an interlocking operator or CTC dispatcher. In timetable and train order territory, they were frequently used at the end of double track that operated by current-of-traffic, and on some single track sections in timetable-and-train-order territory, they were sometimes installed at the ends of sidings used for meets to eliminate the need for brakemen to throw a switch to leave a siding and then line it back after clearing the points. We have also installed them in places where have return loops ("balloon tracks") that we use when operating our model railroad for the public. That way, operators can send a train down the mainline into a loop some distance away without having to be close to the loop watch the train and throw the loop switch while the train is in the loop. This is particularly useful when a single operator is running two trains.

East Bena, center siding spring switch. - D.F. Willoughby photo.

For our spring switches, club member Kent Thaeler modified our switch motor linkage arrangement slightly. Instead of making a Z-link, the .030" wire inserted into the brass tube is bent downward on both ends to form a "U-link." A piece of .024" phosphor-bronze spring wire is then inserted through the hole in the throw bar between the points, with a short bend at the top to keep it from falling through the hole. If the throw bar rubs the sides of the slot it rides in, this can cause too much friction for the light spring tension to overcome, so it's important to be sure the spring wire doesn't pull the points away from the closure rail. A piece of wire (bus wire?) is then coiled around the U-link and the phosphor-bronze spring wire to bind them together, and can be slid up and down to fine-tune the spring tension on the points. By adjusting the position of the coiled wire and the position of the motor on the studs, the tension can be set so that there is just enough tension on the points to move them solidly against each stock rail, but not enough to derail a short freight car weighted according to Club Weight Standards (modified NMRA Recommended Practice).  (Edit by Jason Hill, see LMRC club car standards in my post on Ratings & Operations.)

Spring switch motor installation at Tehachapi. - D.F. Willoughby photo

I've attached two photos showing these linkages at two different locations. There is one minor difference between these two installations. For the earlier one, the coil of wire for adjusting the tension is soldered in place. This makes later adjustments rather difficult. On the second one, the adjustment coil is still movable, but the ends of the U-link and the phosphor-bronze spring have been soldered together, with a large enough blob of solder at the bottom to keep the ends parallel and keep the coiled piece of wire from falling off. Once the spring wire and the U-link are soldered together, there's no need for the bend in the wire to keep the spring wire from falling through the throw bar between the points, and the only way to remove the throw bar is to loosen the switch motor and unscrew the U-link from the roadbed to make it possible to drop the linkage assembly.

The frog sections of most of our switches are less than about two inches long, with gaps at both ends. We generally leave the frogs of our spring switches unpowered. Large steam engines, and diesels that pick up from both rails on all axles have no problem with them at all. Only the smallest steam engines and tenders lose power briefly when passing over the longer No. 9 frogs. If this is a concern, an electronic frog circuit such as Tam Valley's Frog Juicer can be used to power the frog.
There are occasional derailments when there is not enough downward force on a wheelset trailing through a spring switch to push the closed point out of the way. Our car standards specify minimal slack in bolster screws and most of our freight cars use rigid frame trucks and lifting one wheel off the rail wheel lifts the whole truck frame and starts to tilt the car. Cars with loose trucks that are loosely sprung or fully equalized may derail more easily on spring switches, as it takes less force to lift an axle off the rail trying to push a closed point over. Pilot trucks on steam locomotives sometimes require increased downward spring tension, or a small weight glued onto them, to provide enough downward pressure. Two-wheeled pilot trucks seem to be particularly prone to this kind of derailment.

Spring switches can be a bit of a maintenance headache. Problems arise when dirt, dust, ballast or other residue collects under and around the point throw bar. This increases its resistance to movement so that the gentle pressure applied by the phosphor-bronze spring wire is no longer sufficient to reliably seat the point against the stock rail. This residue can often by dislodged by moving the points back and forth vigorously with a finger. If that doesn't work, try removing it with a pick, or by blowing it out using a straw or an aerosol can of air. If the contamination is under the throw bar, it may be necessary to remove the points and the throw bar to clean it out. Tight clearance around the throw bar will make it particularly likely to be sensitive to contamination, and can only be fixed by removing the the points, and the throw bar and carving out more clearance with a knife or motor tool.

So far, we have installed about ten spring switches on the Tehachapi Pass exhibit. Several are used in places that only see service during formal operating sessions that take place about a half-dozen times each year. But the ones on the reverse loops are used daily when the railroad is operated for the public and trains have to go through them at each end of every trip over the mainline. Their convenience far outweighs the disadvantage of their occasional need for maintenance.

In Closing


Thanks to David Willoughby for writing up what the club has done to make our spring switches work.  Most of my experience with the pilot or trailing wheels derailing are usually caused with the leading wheelset trailing through the switch, and trying to actuate the points to move with very little lever moment.  It's pretty interesting to watch a train going over the spring switches and hearing the points snap back to "normal" route under middle of each car going by.

Jason Hill

Thursday, May 6, 2021

SP Jawbone Branch (Part 26) - Engine Spot & Water Track Detailing

Currently, layout construction progress has slowed slightly, but I've been working on researching some other details on the wye.  

Owenyo transfer decks with coaches looking north, circa 1940. - owensvalleyhistory,com - ebay35_owenyo_sml

The Owenyo Local would lay over at Owenyo for the day while the crew rested across the NG in the 'boxcar' hotel, visible beyond the Owenyo station's TO boards.  The mixed train's RPO and coach are resting at left, in the siding.

Owenyo Engine Spot - Cropped from high angle shot from transfer dock pole around 1940 - owensvalleyhistory,com - owenyo dennis burke_sml_r

Zooming in on the above photo shows more carbodies inside the wye, and fairly under exposed oil tanks, a profile of the oil pump house and an under exposed 2-8-0 simmering away "on-spot".  The passenger carbody appears to be either SPNG 7 or 8, a combine with two windows on the short end of the car.  SPNG No.7 became No.17 before she was retired, but it looks like this probably was her final resting place inside the Owenyo Wye.  I may see if I have the space for this little cluster of carbodies around the flagpole.

Engine Spot


A basic boiler watchman would be set or the fire would be cut and hold pressure until the crews went back on duty.  Most photos taken during the day time when the engines aren't switching, show the engine spotted next to the oil tank on the eastern curved section of the wye. 

Owenyo engine spot with SP 2758, oddly with Train 792, I'm not sure the year this could be. - Eddie Sims collection

Notice in the photo, that there appears to be metal plates under the firebox area of the engine.  There was a story in SP Trainline of a new-ish fireman trying to get two 2900-class 4-8-0s refired on an Oregon branchline after the engine watchman wandered off overnight, allowing the engines to go cold by morning.  His inexperience lead him to over fuel the relight of one of the engines... causing oil to spill onto the ground and when the firebox caught the light from his fuzee, the fire spread down onto the ties, into the previously spilled oil and ended up gutting the engine!  The metal under the firebox area here is probably to help prevent damage to the track in case of a fire "dropping" in the firebox down to the track.

The dark dirt/ballast under the front of the engine and leading tender wheel probably from the daily lubrication of the engine before going back to Mojave.  The white area around the 4th driver is probably blow-down scale deposits from the water/mud in the boilers.  Also notice that the ties are rather exposed from the 2nd driver back under the metal plating.  I'm not sure if this is from years of boiler blowdowns right there, or if there is another reason that the dirt/ballast has been left out of this area.  Still it is an interesting thing to model, which I intend to do.

More detail of the engine spot, with spacing for a 2-8-0 to be spotted.

The compression factors on the curved areas of the wye will mean that I can't really have all the space that the prototype photo shows... I'm going to model the features in the photo, mapped out to the size of a C-class 2-8-0, and positioned so that the big 3266 and Mk-2/4s can fit between the small dirt road and as far from the fouling point of the siding as possible.

SPNG 8 Owenyo with oil tanks - Mark Van Klaveren - owensvalleyhistory.com - mark_van_klaveren03_sml

This photo shows some lighter color weathering on the SG oil tank.  There's also some smaller pipe connections on both sides of the 'engine spot'.  I'm not exactly sure what those would be for.  It seems strange that they are back behind the tender, based on where the engines are usually spotted.  Perhaps compressed air.  I don't know why they'd have engine washing stands there.  Perhaps they were compressed air connections to apply forced lubrication into the rods for the return trip.

I guess I also need to figure out where the various power poles need to be mounted, which will make switching some of the areas and navigating my hands into joints a challenge.

Tail Track and Derails?


Of note here is that there doesn't appear to be any derails on the engine spot, where the local engine layed over.  A derail is required on the SP at both ends of any track where an engine is to be left.  Perhaps the SP figured that the placement of the engine spot at Owenyo was different because an engine rolling away would push through the switches at the east end of town and stop against the tank car fuel ramp, and if it rolled towards the tail of the wye, then the tender would go off the end first.

Completed wye tail flex track and wye switch roughed in.

If the wye tail track failed at Owenyo, the engine better be able to pull itself out of the problem.  The nearest relief engine was at Mojave, 143 miles away!  So better to put the tender out on the 'bad track' than the engine.

East Wye Tail


Owenyo SG-NG transfer ramp foreground & "NG Pit" and SG ramp in the background. - Rich McCutchan  - owensvalleyhistory - slim rails63_sml

The east tail of the wye also doubled as the tank car transfer and extended up onto an elevated track, so I doubt that track was "bad", plus there was room for the engine to move out onto that tail farther there.

East wye tail shimmed up with extra tie.

I've been considering showing the start of the ramp to the 'fuel ramp' along side the NG's 'fuel pit' track at the north end (seen in the back of the model photo above).  The main challenge here is that the prototype had, I believe at least one engine length before it started to ramp up.  My model's been compressed a bit more.  The NG track's already dropping down into the bit.  The main concern here is not making too fast of a vertical curve which would cause problems with the pilots of the steam engines planned to be used on the branch.

Water Tank & Track


SP Water cars at Owenyo - Sept 19, 1950 - Chard Walker photo - Mike Massee collection (cropped)

Just east of the road grade crossing to the station, two water cars are spotted in front of the water pump house.  This photo is about four years before the black water tank was moved to Owenyo.

SP Water Tank & Loading Docks - much thanks to Alden Armstrong for permission to use these shots!

In 1954 the water tank at Diaz was removed from the Employe Timetable (ETT).  At the same time a engine service water tank is added to the ETT at Owenyo.

Owenyo SG water Tank - after SG was being razed 1960 - Alden Armstrong

The standard gauge was being torn up back to Lone Pine, but the water tank still stands for a few a little longer.

I'll be looking into contacting the CSRM again about getting the Val Maps for Owenyo, Bartlett and Little Lake this week, so maybe I'll be able to get more information on the size of the structures around Owenyo.

In Closing


I'm hoping to start construction of west Owenyo in the next week or so.  Also the 00-90 screws I need for the switch point bars should be showing up soon, so I can return to working on the track switches.  I've picked up a bit more 14 AWG wire to make the bus wires.  I still need to pick up some plugs to join the track power and lighting strips under Owenyo, between the modules.  Several things to keep working on.

Jason Hill

Related Articles:


SP "Jawbone" Branch Index Page - Links to all my blog posts on my new Jawbone Branch layout.

Saturday, May 1, 2021

New Drawbar Mount for Athearn-Genesis 120-C-6 Tender

In this quick blog I'll be looking into the process of converting Athearn-Genesis 120-C-6 tender for use with standard brass steam engines.

Balboa Models, SP 3266 mocked-up with Athearn-Genesis 120-C-6 class tender.

The Prototype


A quick side note on this prototype, the 3266 was the only Mk-5/6 rated to Owenyo on the Jawbone Branch, which makes it very unique.  Usually 3-4 Mk-2/4s were rated at any point from 1950-1954 specifically by number for operations.  The Mk-5/6s from Balboa are quite common brass models to be had over the last 10+ years.  So this is a fairly easy prototype engine model to make.

SP 3266 near Olancha with excursion to Owenyo in 1952 - Phil Serpico photo - owensvalleyhistory.com - southern_pacific012_t

I don't want to go too far down the prototype rabbit hole here, but the SP 3266 was used in the 1952 fan excursion trip run to Owenyo with the 3237.  It seems from a couple of the photos, such as the one above, the SP 3237 was only needed for the eastward (north compass) trip to Owenyo.  The 3237, may have departed and returned to Mojave, while the 3266 remained in Owenyo with the fan special for two more days.

The 3266 probably was a regular Mojave based engine during that time, normally working the KI (Tehachapi) local and the "Blitz" (Palmdale) local.

The Problem


The SP 3266 Balboa model came with a standard (but incorrect) 100-C-1/2 tender.

Balboa 100-C-1/2 class tender with weird UP-style high-speed trucks.

As far as I can tell the SP swapped all of these smaller tenders to other smaller types of engines.  The SP 3266 during the post-war years was upgraded to 120-C-3/6 class tender, along with most of her sisters also receiving 120-C-series tenders.

However, the brass 120-C-3/6 class tenders are hard to come by... and when they're found, they often command similar prices to that as the Mk-5/6 engine itself!

SP 3266 laying on her side - showing the problem with the tender.

The Solution


Athearn-Genesis unlettered 120-C-6 Tender.

Athearn-Genesis came out with the 120-C-6 tender with their 4-8-2 MT-4 class engines.  They were also made available separately both painted and lettered and undecorated, but painted.

The Catch


The Athearn-Genesis model has a unique drawbar arrangement.

Unfortunately, the Athearn-Genesis model comes with a rather goofy drawbar design... a similar concept to the BLI's articulated cars, which has an open 'claw' on the engine, which snaps around a post inside of the tender, above the frame.  I don't trust this design to handle heavy draft loads, plus the brass engines are equipped with a standard metal drawbar with two holes on the tender side to fit around a pin or screw.

Time to Disassemble!


Due to the large number of plastic parts around the upper shell of the tender, and the front deck plate is fairly fragile plastic, I needed to disassemble the tender with two screws.  One screw is in the middle next to the brake cylinders and one between the rear two axles of the rear truck.

Interior of the SP 120-C-6 class tender.

The interior of the Athearn-Genesis tender is... interesting.  The brass-style drawbar will make things a little tight to have a larger group of wires running between the engine and the tender under the frame.  I'll only be wanting two pairs of wires going to the engine where the decoder is to be located.  Each side of the tender wheels pick up power, and the two wires to the rear headlight on the tender.

New hole drilled with No.50 drill bit, tap for 2-56 screw.

I used a power drill motor with the No.50 drill bit pressing against the tender frame, which I was holding against a piece of 3/4" plywood.  The plywood was needed to keep the fine details, such as the vertical grab bars and ladders at the tender's rear.  A 2-56 tap is then used to cut the threads in the new drawbar hole.

I'll be removing the jumper connection between the engine and the tender.  This requires removing the screws at the front of the large weight stack, and lifting the weights off for now.  The front screw in the PC board is removed and the PC board is lifted up.  Allowing the wire jumper to be unplugged and removed.

Tapped 2-56 hole ready for 3/8" x 2-56 screw.

The 120-C-6 tender is reassembled, ready for 3/8" x 2-56 screw.  I cleared the forward drawbar hole with a No.42 drill bit (clearance drill for 2-56 screw).

SP 3266 with new drawbar screw in place.

In Closing


SP 3266 with completed tender drawbar conversion.

This is not the last time I'll be going into the tender to rewire it and probably adjust the weight balance over the front truck.  The DCC sound decoder in this engine will be in the lower front of the boiler, between the smokebox and the forward of the gear box.  The speaker will be in the smokebox.  This is my preferred method of installing DCC decoders in steam engines, as it keeps the majority of the wiring in the engine and the runs very short.

I'm planning to do a blog post specifically on the DCC installations in brass steam engines, so this post will be kept to just what is unique about the Athearn-Genesis 120-C-6 class tenders.

Jason Hill

Related Articles:




Wednesday, April 28, 2021

SP Jawbone Branch (Part 25) - Wye? - Because

I'm moving the focus of this post back to the construction of the layout itself.  Specifically the wye at Owenyo.  The original plan to drop any concept of a continuous running option results in my absolute requirement to have a working wye at the end of the branch to turn the C-class and Mk-class local engines.

The placement of my station of Owenyo was dictated by the arrangement of the wye in town.  This forced the design of my layout to put Owenyo in either the SE or NW corner of the room.  Because of the bookcases along the north wall, that option was out.  The SE corner was open and the wye could fit between the large desk in the middle of the room and the east wall. 

The new top skin of 1/4" MDF applied to the top of the wye.

Still with the need to keep the shop functional and the options to bring large pieces of material into the work area west of the large desk, I needed to make the wye removable.  Because the layout already needed to have two removable sections for the doors, what's one more removable piece?  For that matter, I just made all the sections of the layout able to be quickly dismantled, if needed.

Structure


Some of these photos have been posted before in the Owenyo #1 structural posts, but they are worth touching on again here, as this is the foundation for the wye structure.

Underside of the Owenyo #1 module, with Wye "Keel Spar" in place.

The Owenyo #1 (East) module will support the tail of the wye as a cantilever, so there's much more support built into the underside of this yard module.

Overview of the bottom of the wye support structure.

Basically all the structural load for the wye tail will be handled by this box structure and an 3/4" x 2" oak "Keel-Spar" forming the structure of the wye module.

The cantilever Keel Spar in place.

The Spar extends out from the far side of the layout about 40".  I tested the spar several times at this point to be sure that it could be easily slipped into the Owenyo #1 module and then back out again.  It is still a good tight fit, requiring both hands; one inside the staging yard and one outside under about where the wye switch will go.  I'm happy with the fit, last thing I want is a loose wye module dropping a brass Mk on the floor!

The End Plate with notch for the Keel Spar mocked up.

Additional MDF support will be added around the edges to support the 1/4" MDF top skin sheet of the wye.

Mock-up of the Keel Spar and the End Plate clamped in place.

This shot gives an idea how long the wye tail will be.  Most recently I have also added a removable 'leg' under the front of the layout, which helps support it.  I may stay with this method, or consider an additional diagonal brace down to the wall brackets to support the very front edge of the box structure. 

During construction of the wye and the switch and track spiking on the wye tail, I had a pair of 2x2s clamped together, forming a support the right height to put under the tail of the wye.  I'd rather not need something like this under the tail permanently, but it is always an option.  Alternately, I could build a folding brace to form a triangle, reaching down to the workbench.  Hinged maybe 1/3rd of the way in from the end of the tail and with a scissor brace locking over-center at the workbench end.  There are plenty of options to add that little bit of extra support.

Spanning the Joint


East curved portion of the wye, the oil tank and engine layover spot are in this area.

I planned to leave out some of the ties across the module joint to the wye.  These locations will be replaced with wood ties, and spiked in place.

Laying out the equilateral wye switch.

Roughing out the flex track coming out of the 26" radius curve.  I reworked the geometery and found that for the No.5 frog, I needed to maintain the 26" radius into the frog, then allow all of the easement between the frog and the headblock of the switch.  It turns out that I had the frog a bit too close to the main line at Owenyo.

After the fact engineering of a No.5 frog on a wye switch.

It turns out that doing the CAD calculations for the placement of the No.5 DTW frog, it should be 2-1/16" from the point of tangent (PT) of the two curves.  The 5-1/2" (40 scale feet) is the length of easement and transition to the headblock of the switch.  This headblock placement could be farther, maybe up to 45ft from the point of frog (PF).

Reworked switch with all ties installed.

I needed to move the frog about 0.300" towards the headblock to get the geometry to work out.  One can see the number of PF's that have been marked from various methods, including offsets from the spiral easements, which aren't needed on a No.5 alignment!

Wye Tail being built from second hand tie sections, threaded on to the tail of the wye.

The wye tail I made from left over flex track tie sections from thinning the tie spacing in the two sidings at Owenyo.  The piece of oak flooring, which makes up the Keel Spar allows for nearly 19" of wye tail.  As there's no other obstruction in the middle of the room, I decided to just lay the extra 5" of track beyond the 14" needed for the Mk-2/4 and -6 class 2-8-2s.

Completed wye tail flex track and wye switch roughed in.

The extreme end of the wye tails often are pretty ratty.  Usually operationally the engines are kept towards the switch end of the tail, with the tender or other cars pushed out onto the 'rickety' wye tail trackage.  I decided to simulate this with increasing tie spacings towards the end of the wye, and tighter spacing for the engine length (about 50ft) closest to the switch headblock.

Cutting the Tail Loose


Pre-stained 8ft ties are glued and slipped under the rails at the module joint.

I hand spiked each wood tie at the joint.  I'll probably end up removing at least one more plastic tie on each side of the joint and getting a little more hand-spiking in to secure both rails on each side.

Close-up of the cut rails on the 26"R curve.

I've tested the wye's 26"R curve with the SP 3203, which seems to be the most finicky of the Mk-series of models when it comes to minimum curve radius.

Separating the wye tail module from Owenyo #1 module.

Good to see that the module slips apart easily.  The long Keel-Spar still holds it in place vertically.  To keep the wye tail from rolling on the Keel-Spar's axis, I drilled 1/4" holes, like I have between the other modules, to accept the alignment pins.

In Closing


Nearly completed wye being held rotationally by the clamps as 3203 is test run on the main.

I probably will still need to do a little fine tuning on the 26" radius curves to get them smooth and consistent and a little more tuning on the module joints in the middle of the curves.

The wiring for the wye will be a fun challenge.  I'm also looking forward to building in some safety interlocks to keep any engines from diving off the ends of the wye when the tail is removed!  I'll get into covering those points in an upcoming post.

Jason Hill

Related Articles:


SP "Jawbone" Branch Index Page - Links to all my blog posts on my new Jawbone Branch layout.

Tuesday, April 27, 2021

SP Tender Swapping (Part 2) - "Tender Migration" Between Shops

In my previous post about SP Tender Swapping (Part 1), we looked at various prototype tenders, and ones that are commonly available to trade between models to get the 'right tender' to match a given photo.

Tender Migration




This time I'm looking at a different take on the "tender swapping" game.  How were tenders moved between the various shops?  What happened when engines were scrapped and the tenders migrated to other divisions to be put behind engines which were still in service?

During the various decades of service from the 1920s, through the 1930s, then the 1940s, and finally in the mid-1950s, the SP's steam engines tended to keep getting larger and larger tenders assigned as the smaller engines were scrapped.

An early photo of SP 5000 with the single 120-C-3 class tender.  Most of the SP-series of engines received 120-C-5 tenders. - Eddie Sims collection

It's hard to believe that the SP (4-10-2) class engines were delivered with 120-C-3 and -5 tenders, during the swaps of the late 1940s, they received 160-C types instead.  Many of the SP's F-class 2-10-2s also traded up their 120-C-series tenders for 160-C types during the 1950s.

A few SP 'Decks', such as F-4 class 3704, received very large square tenders from the AC-9s or foreign roads, for use in desert territories. - Eddie Sims collection.

In some cases, engines such as the AM and AC-1/2/3 classes were scrapped and their tenders filtered down to F-1, Mk-2/4, Mk-10/11, and various other engines.  As the AC-4s and 5s were retired even larger 160-C class tenders became surplus and were transferred to other smaller engines, then those tenders moved down to Mk-2/4 and 5/6s and C-classes.

SP 2771 with a 120-SC-series tender off an AC-3 or AM-series articulated.  This one still has the pressure cap on the oil bunker! - Eddie Sims collection.

These shuffles resulted in some weird combinations, such as C-class 2-8-0s receiving 120-SC-series "whale-back" tenders!

SP Tenders Away from their Engines


SP 4279's tender is set aside while the engine receives a new set of flues and rebuilt super-heater unit

Spare tenders for another AC and a GS also rest in the 'Garden' at Bakersfield while the engines are in the backshops.

The SP 'Malley Shed' at Bakersfield, which was used as a heavy car shop after the 1930s, usually had a half dozen or so tenders stacked into one of the open-air stub tracks being worked on or stored waiting for their assigned engine to come out of the backshop facilities at Bakersfield.  A few could also be seen over in the 'Whisker' tracks on the west side of the turn table at the electricians shed or stored for a 'quick' flue job, such as on the SP 4279 in one classic shot from the roof of the water tower.

The Prototype Photo


Here a set of F-units approaches Tunnel 2 with the (Mojave) "Shorts", notice the pair of tenders at the right of the photo. - E.K.Huller photo

In the photo above a pair of tenders are being moved from Bakersfield or west of Bakersfield to Los Angeles.  It is also possible that the tenders in the photo are set of tenders assigned to MW service.  The pair of tenders appear to both be 120-C-2, or possibly 120-C-3/6 class tenders.

Sunset 120-C-2 tender

These could be made with either Sunset, PSC, or (in the case of the 120-C-6 tender) Athearn-Genesis spare tenders.  - Unfortunately, most of the 120-C-1/2 tenders around my shop are all claimed for various engines.  

Athearn-Genesis 120-C-6 tender for SP 3266

A pair of Athearn-Genesis tenders would make a very nice starting point, but the $70+ list price per tender starts making that a bit painful.  Unfortunately the Athearn-Genesis tenders that are in 'the pool' are already claimed by other engines.  Some of those tenders could of course be 'borrowed' until their engines are finished and the DCC installed, etc.  However, I'd rather not have to retouch the numbers on the back of the tender.  From some photos in Robert Church's books on the Ten-Couple and 4-8-2 Mountains, these tenders when unassigned usually had their tender frame numbers painted on the backs of the tank. - I assume that during transfers between the shops, this would be the method used to keep track of them.  Of course any tenders in SPMW service would carry their own MW numbers.

SPMW 8241 built from an MDC/Roundhouse 70-C-1/2 tender

On with the Project!


The easiest... and probably prototypically lazy way to deal with the problem of where to get your 'spare tenders' from is to do just what the prototype did.  Use your supply of extra tenders you're not using with your engines!

Spare Sunset Models 70-C-9 class tender

In my current case, there are a couple of extra tenders from Sunset M-6/M-9 class 2-6-0s which could use new homes, but by the late 1940s and early 1950s, the super small 70-C-9/10 class tenders were mostly relegated to small 0-6-0s.

SP 2757 with 70-C-9 tender after WWII. - Eddie Sims collection

In some cases 2-6-0s and even 2-8-0s were assigned these small tenders when assigned to local yard work.

SP 2718 with 100-C tender by post-WWII era. - Eddie Sims Collection

However for my purposes the 2-6-0s and 'bigger' C-8/9/10 class 2-8-0s working out of Bakersfield generally had the larger 90-C and 100-C size tenders, and my little SP 1213 already has a little tender!

Tender book, that I used to find the tender frame numbers for these tender classes.

Looking at Southern Pacific Historical & Technical Society's Tender Book, I find that SP had only two tenders rebuilt to class 70-C-10, so these more rare tenders probably wouldn't have ended up coupled to each other in a transfer move as I'm considering modeling.  Ideally then, the spare tenders could be a 70-C-9 and a 70-C-10.

Painting and Weathering Choices


In the photos in Robert Church's books some of these unassigned tenders are obviously fresh out of the paint shops after rebuilding.  Some could have been stored for weeks or months before being assigned to a new engine or ordered to be transferred to another shop for assignment.

Here's an example of a traded tender, freshly cleaned, behind a dirty SP 3266.

The tenders probably would get a bit of running weathering en route, but would be given a quick wash down or steam cleaning before having their new engine number painted on the rear of the tank.

Tenders coming through this process would probably have a slightly different 'patched' appearance on the rear of the tank where the new road number is applied over the tender 'frame number'.  This is another detail which can be added to your paired steam engines and tenders.  As you change your engines and tenders around this prototype 'patch' painting work can be used to hide the fact that you've swapped tenders, without completely repainting a tender from scratch.

Painting the 70-C-9/10 Class Tenders



Sunset Models M-9 class 2-6-0 with proper replacement 100-C-1/2 tender.

Both of the 70-C-series tenders for this project came from Sunset M-6 and M-9 class 2-6-0s.  These tenders are too small for the prototypes my customer and I wanted to build them to be.

SP C-70-9 and -10 class tenders

Other side of the two tenders.

I mocked-up the two tenders with Tichy Andrews trucks.  For rollablity as cars and the fact that the metal trucks were needed to go under the Balboa 100-C-1/2 tenders.

SP 6855 & 7067 tender numbers in place of locomotive numbers. 

SP painted the tender frame numbers on the tenders when they were not assigned to specific engines.

Mechanical Changes


Mechanically the changes required will be very minimal.  On the prototype, obviously the stacked drawbars (one above the other) would simply be connected to the other tender instead of to the rear of the engine frame.  I'm sure the extra drawbars could be loaded onto the tops of the tenders or otherwise coordinated between the shops to have the proper number of drawbars at the receiving shop to connect the engines with their new tenders.

Tenders drawbarred in this version with a piece of PC-board.  I may replace this with brass section.

Generally the brass tender models have a threaded post at the front of the tender which slips through a hole in the engine's drawbar.  For this conversion I'll be swapping out the 1.4mm threaded rod-pin for a screw and a drawbar to keep the two tenders together.

The main consideration with using brass tenders in this way is that there is NO INSULATION between the tender frame and the drawbar pin.  Using a metal drawbar will cause a short between the two tenders.  One of two things must be done for this configuration to work: 1. swap the pickup side of the tender trucks to the 'wrong side' or use of a insulating drawbar or draft gear box for one or both ends of the drawbar.  Thankfully in most cases, converting these cars to plastic trucks should solve these electrical issues.

Truck Bolster Shims


Tichy Andrews trucks, 0.03" bolster shims, and some 1.4mm screws for the bolsters.

The Tichy trucks are lower at the bolster than the previous Sunset Models brass trucks, so I need to shim the bolsters up to fix the coupler heights.

Coupler Box Shims


SP 7067, 70-C-10, tender ready for the road.

I shimmed the coupler boxes with a small piece of 0.02" x 0.04" styrene cut to 21" long.  A little touch up paint could be used along the outer edge of the shim.


Coupler height adjusted on SP 7067.

A bit of adjustment was also needed to the rear pilot footboards, which looked like they got tweaked a bit somewhere along the line.

SP 6855 coupler height after shimming.

I may eventually put leaf-springs in the Andrews trucks, but for ow the cars will do.

In Conclusion


If for any reason in the future I might want to split up the tender transfer pair, ideally, this should be as easy as dropping the drawbar off one of the tenders, swapping back to the pin, and a quick patch job over the rear of the tank to reapply the new engine number to the tender.  Flipping the insulating side of the trucks on one tender is just asking to be forgotten about in 5-10 years when you might want the tender with another engine again, which is why I'm avoiding that option.


Hopefully this has been a quick fun project, and a way to 'use up' those spare tenders which aren't quite right for any engine in the current stable.

Jason Hill

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