ScaleTrains SD40-2 Railhead Rubbing Problem - Easy Fix Link

[spookshow]

I'm starting to think that this doesn't have anything to do with the speaker or its contacts at all (at least not in my case). I flipped the speaker over so that the contacts point up instead of down, made sure it was seated all the way inside of its little cavity, and the fuel tank still bottoms out. Frankly, I just think it rides too low.

Maybe if I run it around in circles long enough it'll wear a groove in the plastic and stop bottoming out.

-Mark

[garethashenden]

Your third axle is off the rails. Maybe the front one too? Might cause some clearance problems.

[Chris333]

I know nothing about these, but I see air between your tank and frame right behind the bell.

[spookshow]

Your third axle is off the rails. Maybe the front one too? Might cause some clearance problems.

Here, all wheels on rails -



-Mark

[spookshow]

I know nothing about these, but I see air between your tank and frame right behind the bell.

The front section of the tank does not sit over the speaker enclosure, so you do see some light up there.



I wonder what would happen if I got rid of those ridges on the bottom of the tank?

-Mark

[spookshow]

Getting rid of the ridges helped quite a bit. It still nicks the rails at grade changes, but not enough to bring it to a halt. If I hadn't spent the past few weeks dealing with the problem I might not even notice it now.

-Mark

[spookshow]

Since the endcaps on the fuel tank hang down a little further than the tank proper (which you can see in Bob's photos), I went ahead and filed grooves in said endcaps to provide more clearance for the rails to pass underneath. And this seems to have finally solved the problem for me.

I gotta say, I think it was extremely short sighted to hang that tank so close to the rails and just assume that it wasn't going to cause problems for people.

-Mark

[chessie system fan]

Mark, just as a comparison can you post a picture of a Kato (or perhaps a different brand) SD40-2 at that same location?

The ST fuel tank end caps actually look a bit overscale to me. I suspect they exaggerated the effect so people could see them and this is contributing to the clearance problem. 

[kiwi_bnsf]

The front section of the tank does not sit over the speaker enclosure, so you do see some light up there.

-Mark

Thanks for posting the additional pics of your problematic fuel tank.

From the profile pic it really does look like the tank is lower at the front as compared to the rear. That daylight you can see looks like the insert in the fuel tank that fills the underframe gap is too high towards the rear, or is not sitting flat in the inside of the tank…




I wonder if it is possible to re-seat the insert (is it glued or screwed inside the fuel tank)?

Or failing that give the rear surface a few swipes with a file to see if you can snug up the front section of the tank more tightly against the frame…




Hope this helps!

[robert3985]

It appears that there are two elephants in the room.

The first elephant is that Quality Control failed somewhere in the production process of assembling this model at the manufacturer.  If there's residue slopped or scraped onto the flat bottom surface of the frame/speaker-enclosure, then the plastic fuel tank is going to be tilted, and will probably rub along the railheads until it finds a gap in one (or more) of the rails or if there's railhead uneveness...even just a bit...and the engine will catch that and stop moving, even though the motor will still be running and the wheels turning.

The second elephant is that this engine doesn't like grossly uneven, mismatched track joints, nor sudden, badly laid grade transitions, nor grade crossings with between-the-rail boards that are higher than the railheads, even when the fuel tank is properly installed.

The ScaleTrains SD40-2 is a superbly detailed scale model N-scale engine, and on my layout, with its Code55 Rail Craft flex, even, soldered rail joints (using cut-down, tight Rail Craft/ ME joiners) grades that have a vertical "spiral" transition at the beginning and end, substantial sanded subroadbed with sanded cork roadbed to which the flex track is glued to...and with the same quality hand-laid Code40 Branchline trackage...it runs flawlessly.

On the other hand, on Nate Goodman's old Riverside layout section (now at a new home) with some rail joints that were damaged in moving, Code80 Atlas flex, Peco80 Insulfrog Turnouts...it also runs flawlessly and it was the star of the get-together on Friday night, with it running in either direction, pulling/pushing an old Masonite track-cleaning boxcar for at least three continuous hours.

Sure, if you kink your unsoldered sectional/Kato track at the joint, with one set of rails at least .026" to .030" above the railheads on the abutting track section, there might be some problems...but, that is BAD trackwork...and I would never allow that gross of a railhead difference, nor a ski-jump like that to exist on any of my model trackage that I laid for myself or for my friends/customers.

I think the conclusion here is that ScaleTrains design and intent is to run their scale model N-scale engines on scale-model track, that's laid at least semi-well, not on toy sectional track on your carpet, table-top or tatami mats with .030" pieces of Styrene tucked under the rail joint.

This is a "scale" model, and isn't intended to run on toy trackage or grossly unevenly laid trackwork.

In my way of thinking...of course tilted towards more realistic-looking and operating model trains...this isn't a negative point for ScaleTrains engines.  I am quite certain they realize that by designing their engines to more prototypical dimensions and clearances, there are going to be both consumers and layouts that are not comfortable running their products.  On the same side of the coin, because of the tighter clearances, and much more assembly required at the manufacturer, ScaleTrains will run into many more potential problem areas because of the increased difficulty in producing a "scale model" rather than a much less correctly detailed product...and I commend them for their persistence and vision in bringing to us N-scale modelers such a definitive choice by producing their fabulously detailed and accurate models at a decent price.

For me, my 15 minutes of figuring out how to get the fuel tank level and then doing it, was well worth that little bit of time and effort because of the enjoyment I, and my model railroad friends, got out of looking at, and then running this model for three straight hours after it was "fixed".

Here are a few more photos of this model at Echo Curve on my layout...















My only problem is that I won't be buying any of these because they're much too modern for my layout's Transition Era time period....DAMN!

ScaleTrains...I'm still waiting for the Verandas!

Cheerio!
Bob Gilmore

[robert3985]

Thanks for posting the additional pics of your problematic fuel tank.

From the profile pic it really does look like the tank is lower at the front as compared to the rear. That daylight you can see looks like the insert in the fuel tank that fills the underframe gap is too high towards the rear, or is not sitting flat in the inside of the tank…




I wonder if it is possible to re-seat the insert (is it glued or screwed inside the fuel tank)?

Or failing that give the rear surface a few swipes with a file to see if you can snug up the front section of the tank more tightly against the frame…




Hope this helps!

When I disassembled the problematic ST SD40-2 I had in my possession to figure out if I could easily fix the fuel tank rubbing problem, I thought, at first, that maybe filing down the front of the top of the fuel tank or scraping off the two interior "ridges" might give extra clearance under the fuel tank after re-assembly.

However, after looking at the design of the fuel tank and how it mates to the engine's frame/speaker-enclosure, it became apparent that, first, the front part of the top of the fuel tank doesn't touch the frame, and isn't designed to touch it...in fact, that little piece is there because the prototype fuel tank has a space between it and the frame at that point...and secondly, that the two "ridges" inside the fuel tank were there to space the fuel tank away from the speaker's back surface and to position the fuel tank centered from left to right...being placed between the vertical surfaces of the speaker enclosure...not resting on the flat bottom surface of it.

Unless the speaker itself was mounted wrongly, protruding downward too much for some reason, shaving off the ridges wasn't going to help anything.

Since the problem was pretty obvious when looking at the engine at eye level while it was sitting on level track (not grossly kinked track) that the front of the fuel tank was rubbing the railheads...and the rear of the fuel tank was high above the railheads, it became apparent to me the solution was to get the tank EVEN...not raise the entire assembly any higher...just the front of the fuel tank.

Photo (1) - Un-fixed fuel tank with the front edge of it rubbing the railheads on even, level, flat trackage:


As you can see from this photo, the front top of the fuel tank is nowhere near touching the locomotive frame...so filing it would not have done anything at all.

The culprit was a glob of solder/flux that had been slopped/swiped on the flat bottom of the frame/speaker enclosure near one of the speaker solder tabs...and then had been painted over so it wasn't blatantly obvious there was stray solder sticking to the flat bottom of the frame/speaker enclosure...making a lump there so the fuel tank would not fit flush against the flat frame/speaker-enclosure bottom surface as it should have.

Photo (2) - Flat bottom of the frame/speaker enclosure showing the speaker solder tabs and the bare-metal spot where I cleaned away the solder/flux glob stuck there:


You will note that I also chamfered the threaded mounting holes to eliminate any burrs or metallic extrusions from the threading process to make sure the fuel tank would be flat and flush with the frame/speaker-enclosure bottom surface.

After making sure the screws would seat fully into their threaded mounting holes, I reassembled the fuel tank to the frame, took a look at the engine again at eye-level and noted that the front of the fuel tank was no longer rubbing the railheads and the fuel tank appeared to be parallel to the railheads with adequate clearance space for minor irregularities in railhead height.

Photo (3) - Fixed ScaleTrains SD40-2 with properly attached & positioned fuel tank above the railheads:


Since I file my hand-laid turnouts when constructing them to make sure all the railheads are even after soldering to their respective PCB ties, and I file my soldered rail joints when putting two pieces of flex track together to ensure the railheads on either side of the joint are even, my thoughts are that this under-the-fuel-tank height above the railheads is sufficient for proper operation...and if it were to catch somewhere on my layout, the fault would be with the track...not with the engine, and I would attack the problem by re-soldering and filing the railheads even at the problem spot.

For full instructions, use the link in my first comment in this thread to read the complete process.

Cheerio!
Bob Gilmore

[Mark5]

Here, all wheels on rails -



-Mark

That is one scary looking rail joint!  Maybe my eyes are deceiving me, but one rail appears to be at least 0.025" higher than the other.

Mark

[wazzou]

That is one scary looking rail joint!  Maybe my eyes are deceiving me, but one rail appears to be at least 0.025" higher than the other.

Mark

I’ve mentioned that too.

[ridinshotgun]

For all the crowing in this thread about this is such a supe duper ultimate model that ST puts out I will say that the gap between the tank and rail looks off and not to scale.  Here is a real SD40-2 (but I am sure someone will have an excuse on why that picture doesn't represent real life.)

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[Chris333]

Well yeah the tank is on E.