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One issue that I've struggled with on TMCC and DCS upgrades, and even on some stock Lionel dual stack steam is getting the smoke to flow reasonably even between the two stacks.  It seems like they're never in sync, either the front stack or the rear stack has most of the smoke.  Some of the worse offenders are the otherwise really nice JLC Challengers!  Another one that has very poor distribution is the LionMaster T1 Duplex and the other LionMaster models with the same stack design.

I have a 3rd Rail Big Boy on the bench for an upgrade, and I decided I needed to figure out a different scheme.  I happened across the Hot Box Reefer smoke unit body on the Lionel parts pages and an idea hit.  It has a hose coming out the side, and there's a PCB with the smoke resistor with no stack hole.  However, I didn't want that, so I used the standard rectangular smoke unit PCB with the hole.  I mounted a short piece of brass tubing in the stack hole of the PCB, and then I cut the side hose to size, put a spring inside it to keep the hose from kinking and shutting off the flow, finally I inserted a short piece of brass tubing in the end of that one.

The final piece of the puzzle is that neat 3D printed stack assembly that Bruk nicely had printed for me, it was a perfect fit in the stacks of the Big Boy.  I use it to align the two brass tubes, and the whole assembly will be inserted into the boiler of the Big Boy.

The mod works perfect, both stacks have a generous smoke flow, it's the best solution I've come up with so far to even out the smoke!

Dual Stack Smoke Unit Modification N1Dual Stack Smoke Unit Modification N2Dual Stack Smoke Unit Modification N3

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  • Dual Stack Smoke Unit Modification N1
  • Dual Stack Smoke Unit Modification N2
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One issue that I've struggled with on TMCC and DCS upgrades, and even on some stock Lionel dual stack steam is getting the smoke to flow reasonably even between the two stacks.  It seems like they're never in sync, either the front stack or the rear stack has most of the smoke.  Some of the worse offenders are the otherwise really nice JLC Challengers!  Another one that has very poor distribution is the LionMaster T1 Duplex and the other LionMaster models with the same stack design.

I have a 3rd Rail Big Boy on the bench for an upgrade, and I decided I needed to figure out a different scheme.  I happened across the Hot Box Reefer smoke unit body on the Lionel parts pages and an idea hit.  It has a hose coming out the side, and there's a PCB with the smoke resistor with no stack hole.  However, I didn't want that, so I used the standard rectangular smoke unit PCB with the hole.  I mounted a short piece of brass tubing in the stack hole of the PCB, and then I cut the side hose to size, put a spring inside it to keep the hose from kinking and shutting off the flow, finally I inserted a short piece of brass tubing in the end of that one.

The final piece of the puzzle is that neat 3D printed stack assembly that Bruk nicely had printed for me, it was a perfect fit in the stacks of the Big Boy.  I use it to align the two brass tubes, and the whole assembly will be inserted into the boiler of the Big Boy.

The mod works perfect, both stacks have a generous smoke flow, it's the best solution I've come up with so far to even out the smoke!

Dual Stack Smoke Unit Modification N1Dual Stack Smoke Unit Modification N2Dual Stack Smoke Unit Modification N3

That looks really good and seems effective. I see you are using Bruks smoke unit parts👌.

The trick would be fitting it in.  Since I'm putting it into a empty brass boiler and I have to build the mount anyway, I know it'll fit.  For an existing locomotive, you'd have to evaluate the positioning and see if you could make it, the smoke unit position would be slightly back from where it is currently to line up the smoke opening with the rear stack.  If that can be accomplished, and the 3/8" slide backwards of the smoke unit works. I don't think there should be an issue.

I just completed installing John's S-C and C-G and tuning the smoke unit on my JLC Challenger 6-28099.  (By the way John, thanks again for your help with the install).  Here are some of the things I did and the results thereof.

The intake hole was enlarged to 7/32nd" (above the fan).  I went with this size to match the approximate diameter of the inner fan blades opening.  Any larger and I thought the inlet hole would start to expose the fan blades resulting in a less efficient air flow.

The exhaust was enlarge to 5/32nd".  The exhaust hole enlarged is in the casting that attaches to the top of the smoke unit.  I wanted to reduce the discharge restriction without causing the casting to come loose.  However, as this casting is held in place with screws, I probably could have made this larger.  I also replaced the batting and tested the resistor, which was original and still tested and looked good. I also oiled the fan motor upper sleeve bearing.

The attached photo shows the holes enlarged.  Notice the shinny interior of the exhaust stack showing the metal removal. I wish I had recorded the original diameter of the holes.  I could have then calculated the % increase.

What I found is the smoke output was greatly increased.  So much so i now have to turn the smoke unit off to clear the room of smoke after only several minutes of run time.  I also noticed the exit velocity of the smoke has increased.  On this particular engine there is a wedge divider/diverter right above the smoke unit's discharge.  This splits the smoke flow into the two exhaust stacks.  When in idle, the smoke flow seems to be fairly even, with maybe the back stack with a little more flow.  But, to me, very acceptable.  With the engine running (chuffing), the amount of smoke from each stack, again seems to be the same.  I will note, that the increased air velocity going through the lower internal diverter, pushes the smoke forward and back.  In other words, the smoke does not go straight up.  Here again, there seems to be the same amount from each stack.

Let me know if this is of help to anyone.

20210123_17123020210125_141558

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  • 20210123_171230: Modified intake and exhaust on smoke unit
  • 20210125_141558: Idle smoke
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