Can anyone explain the purpose of the blue wires shown on the rear of the cylinders on a Bachmann 3 truck shay. I have the wiring diagram from Bachmann, but I see no reference to this connection. Any assistance would be greatly appreciated.

Hi Dan, I believe these are the chuff triggers. Find the other end inside the bunker and you connect these to the chuff input on your sound system. Half the time they do not trigger correctly and a lot of us choose auto chuff.

Don

Thanks Don. That had crossed my mind but I wasn’t sure. I’ll hook them up and see if they work correctly. If not, I’ll take your suggestion and use auto chuff.

There’s a lot of weird stuff associated with those contacts… we need TOC… I seem to remember the tension of the contacts caused noise or clicking…

are you thinking of using the triggers?

Greg

…

Greg, I would like to use the triggers, but if it causes other issues I am ok with leaving them disconnected. I am going to go ahead and run the wires and decide later wether to use them or not. I am using a Phoenix P8 board if that makes any difference. Thanks for your help.

I have my shay wired to the triggers and it works fine.

Thanks, Chris. Your shay sounds great. How does it sound at lower speeds?

The cool thing is that they trigger right in time, and of course you get the correct number of chuffs as compared to the actual motion.

I have heard, that they get out of adjustment/stop making contact sometimes, and can “bounce”, but the sensitivity to bouncing is dependent on the sound card, and newer stuff seems to ignore bounces better.

You gotta remember these babies spun pretty fast at slow speeds, so sound really different than a “normal” loco…

Chris, did you verify that all 3 contacts are working? The sound is very “even” so that would say yes, but it seems that the chuffs I heard were not 3 or 6 per crankshaft revolution… you should get 3 triggers per 360 degrees of crankshaft (although shouldn’t there be 6 chuffs)…

All my curiosity aside, it sounds very nice.

Greg

Dan Hilyer said:

Thanks, Chris. Your shay sounds great. How does it sound at lower speeds?

I will try to make a bench top video for you this week to show how it works at lower speeds.

All Shays.

Tension of contacts on piston pushrod causes crosshead to rock in guides, especially units that have not been regularly lubed.

Causes knocking noise.

Big failure is one of the tabs the wire solders to on the contact strip breaks off (easy to fix once you get the entire cylinder assembly off).

Chuffs are NEVER right…they are exactly 1/2 the number. Remember, steam cylinder exhausts at each end the throw of piston.

You will learn how to re-tension contacts in situ by popping cylinder covers off and pressing down lightly on top contact with that piston down.

Sometimes rotating the slip joint 1/4 turn from front truck will smooth out erratic chuffs (action of u-joint on crank).

Worn crank and journals makes chuffs erratic.

Phoenix used to say set the chuff on the opening of the contacts to make it smoother.

Cannot remember how I used to do that.

Wait until one of the contact tabs breaks off and falls inside the cylinder.

Learn how to remove cylinder/engine assembly. Rotating locks, screws, and valve gear retainer tab.

Do NOT shorten the wires to the point they are tight or you won’t get it off without cutting/removing wires.

BTDT

I’ve been using these contacts since first version (upright GOR bulbs in headlights), two of said units running on the CCRy.

TOC

Thanks TOC! That confirms my thinking that one contact on each cylinder is only detecting 1/2 the power/exhaust “strokes”.

So, maybe if you really wanted prototype number of chuffs, you would have to have a sound card that “doubled” the chuffs that were “reported” by the contacts. I’ve seen a few DCC cards that can do this.

In reality, since very few sound cards can alter the chuff sound duration realistically for higher speeds, running at 1/2 the prototype rate is often the best compromise between exact fidelity to prototype timing and the chuffs not blending together at higher speeds.

Greg

Very good info, TOC. I can now take the cylinder assembly off in my sleep. Except for the cylinders themselves and the trucks, I’ve taken this thing down to its individual pieces and now putting it back together. I have replaced ALL the wiring. Again I appreciate all the help. Thanks.

I have never converted mine to a multi trigger setup. I was going to do it once the factory trigger set quit working, but 7 years later it still works fine and I’m use to it. Shay sound tends to blend together once it speeds up, and the 6 chuff pattern is less distinguishable.

Here is the same setup, 4 years after installation with no changes. Still sounds the same today.