October 17, 2010

It's too cool for shorts!

I wired up the last three turnouts at Brook using a second Hex Frog Juicer.  These were the last frogs that needed to be wired in the main room. So I decided to test them. I fired up the Haupt, the only engine I have right now that has a decoder. It has been a good runner. But in today's test, it would not run well at all. It was stalling and shorting in places where it ran well earlier. The shorts seemed to be coming from the front truck.  So started several hours of debugging, but in the end I think I found the problem.  I'll provide some more detail in case you run into similar problems on your locos.

The wheels on the engineer side of the Haupt are electrically connected to frame. The wheels on the fireman side are insulated at the hub. There are no wipers on the fireman side of the drivers. There is a single wiper on the pilot truck to pick up power from one axle. The whole frame is hot. If the pilot wheels or drivers on the fireman side touch the frame, there can be a short.

The pilot truck has an oblong curved slot in the top sheet between the truck frames (this is a part on the model only. The prototype doesn't have this piece as its front suspension is much more complicated). Through this slot goes a special stud type screw that attaches to the bottom of the boiler. The screw holds the pilot truck on the loco, but the truck hangs somewhat loosely. There is a cylindrical brass spacer and a spring to provide a bit of suspension. The first problem I noted was that this spring was partially stuck in the oblong slot and not fully engaged. I made washers out of 0.022 inch resin impregnated paper to give the spring a place to rest and to prevent it from getting stuck in the slot. I also added three washers at the top of the spring to help the front of the loco to ride a bit higher providing clearance for the wheels. This also seemed to help the tracking of the truck but it did not solve the shorts.

I tried running the loco, but still was getting shorts. I removed the front truck and the loco ran without problems. 

I put the front truck back on, turned the room lights out and tried running. I got shorts and could see sparks. I removed the loco and carefully inspected it. I found scorch marks in two locations, both on the fireman's side. One was on the front of the fireman's side cylinder where the wheel sometimes rubs on curves. The other location was on the bottom of the cross head guides.  See the photos.  

It appears that as I ran the loco the paint in these locations wore off. Where the fireman wheels touched the bare frame, shorts  happened and created arcs.   The crosshead needs to be lubricated as friction here will prevent the drivers from turning as it moves down the track. 

Using the laser I cut a paper insulating ring  for the front of the cylinder. It's the white ring in the photo. I added insulating strips on the crosshead guides (see the first loco photo). I also painted the back plate of the crosshead in case that touched the wheels. I only had to do these fixes to the fireman side as the engineers side is all hot and rubbing doesn't cause a short.

I also removed the wiper on the pilot truck because it started smoking during one of the shorts. The wiper is held in place with an insulated plastic sleeve that prevents the screw from touching the metal (and hot) frame of the pilot truck. I think that this sleeve was compromised when I removed the wiper.  It doesn't seem to hurt the loco's running.

After I reassembled the loco, the head light doesn't work. I didn't try fixing that, as I will need to rewire it for DCC when I get a sound decoder for the loco.  I'm not sure if the bulb is burnt out or the cut wiring to the pilot truck is the cause. It is actually fairly easy to replace the head light. The smoke box door pops off and the light bulb is a slight friction fit in the headlight housing.

I have not added the wipers on the tender for the engineer's side. The McCallum has wipers on both sides of the tender. Thus the tender will run by itself. The Haupt's tender will not run on its own as it relies on engineer side pickup from the engine.

All three of my Mason locos have had problems with the front truck. It seems like a better suspension might help with the tracking. Slightly smaller wheel flanges and insulating the cylinders may also help prevent the shorts. 

Finally, with the engine reassembled, I did some test running and it is working nicely now. The frog juicers work flawlessly. If only all model railroad wiring and track was so easy. Duncan McCree at Tam Valley Depot really has created a great product with these circuits.  On the other hand, the locos are beautiful, but temperamental little beasts. Kind of like a....... 


  1. From my experience with the SMR Atlantic, I'm fairly sure the pilot wiper is the fireman's lead to the headlight only.

  2. I think you are right, but it doesn't explain the black plug in the boiler shell. I removed the firebox and that gave good access to the internal wring. It will be a easy to add th speaker and working headlight once I get a sound decoder.

  3. Bernie:

    I don't nave any of the SMR 4-4-0's and can't comment on their construction, but I have found two books on British model loco construction helpful with setting up the O Scale 0-6-0 kit I am working on: Guy Willimams' "The 4 MM Engine, a Scratchbuilder's Guide" (out of print: I think I got mine through Abe Books) and Iain Rice's "4 MM Etched Kit Chassis Construction" (Wild Swan, still in print, I used International Hobbies in Auburn CA.). I may not have the names right, but they should be close. Both deal with a different scale, and they assume a different type of frame (thin plate v. thick bars) than we tend to use, but 4-4-0's (as well as 0-4-4's) were common in the UK and they both have ideas for mounting the front truck and balancing the puppy.


  4. I ordered a copy of Ian's book. I also had a nice talk with the fellow at International Hobbies. One of my long term objectives is to build my own loco. IH is the US source for many UK loco parts, like Slaters. Though you can order internationally from Slaters, it is nice to have a live person to call and ask advice. So I plan to patronize them.

  5. Bernie:

    I have had very pleasent experiences with IH as well. I had not, however, realized that they were carrying Slaters and other useful parts so this is good to know.

    When I caught the loco building bug, but realized I was far from ready to tackle scratchbuilding, I took the plunge and bought a kit (an SP 0-6-0 switcher) from Stevenson Preservation Lines (he is on the Web). It is an interesting half way point between modern kit building and scratch building: it is essentially a late 30's design with a number of parts updated with new drive train, English pre quartered wheelsets and new etched and cast parts. Instructions assume a fair amount of knowledge of steam engines and classic modeling technique and a lot of clean up and, depending how anal one wishes to get, adaptation of parts is required. A scratchbuilder's approach to researching and thinking through proceedures helps enormously. For a newbie like me who doesn't do well following instructions, it is a big project.

    The upside is that even though I am far from finished, my soldering, metal forming, and loco building skills, knowledge and confidence have increased enormously as a result, so it has been great training (and a lot of fun) and I am already thinking about future scratch built projects.

    I mention Stevenson because Bob Stevenson is a real nice guy to deal with and he is rolling out brass castings for a 19th century Central Pacific/ Virginia and Truckee style 4-4-0. No kit as yet, and I don't know whether wheels and other drive components are available, but something to keep in mind when the building itch gets unbearable.