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Discussion Starter · #1 ·
I picked up a 2nd hand near new Bachmann K-27 a few weeks back and finally got round to giving it a run. I don’t like smoke generators for two reasons, the residue it leaves and it doesn’t look real enough to me, so I just don’t bother.

The previous owner of the K had already used the smoke because I could see oil stains so I thought I would give it a go.

Now this is where is got strange, I’m 90% sure the fan which should blow the smoke up was sucking it in? Has anyone else had this problem? I’m sure a simply wire swap will make the fan run the other way.


 

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Nothing strange here. Just another Bachmann stuff up.
Yes, the motor cooling fan does suck the smoke down the stack.
A simple wire swap will not work. The fan used is designed to only rotate one way.

Fixing it means dismantling the boiler. Not a job for the faint hearted.
The fan is mounted back to front and needs to be remounted so that it sucks cooling air up past the motor. That air then blows up and out of the stack producing copious quantities of smoke.
 

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Discussion Starter · #3 ·
Thanks Tony, was it was a batch error or just a few mishaps in the factory?

When I get round to installing a decoder and sound systems I will probably just remove all of it all together. I am preparing myself soon for the not so faint hearted job!
 

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Pardon the dumb question, but haven't there been 2 runs of the K27? If so, wonder why the fan direction has not been reversed, unless Bachmann believes the air flow is critical to cooling the motor over proper smoke function.

Anyone confirm?

Regards, Greg
 

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Greg.
Yes there have been two batches.
Later versions have had some modifications made to them, like corrected cab doors and new tender trucks. No change to the fan that I could detect in the second batch

The fan is above the motor. The laws of physics would suggest that as hot air rises, it would be more efficient to suck the hot air upwards to cool the motor, than to try and force it downwards.
It is simply a by product of the internal design that if the fan sucked air upwards it would find the path of least resistance to be out via the stack producing copious amounts of smoke. Which is the exact opposite of the path it now uses.
The problem is the screws used to mount mount the fan will be the wrong length if it is mounted the other way around. Only two can be used.
 

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I have a couple of questions.

1. How inportant is the Fan? Can you run with out it?

2 Can the smoke machine be removed with out removing the fan?

3. The fan would have to run only one direction. If you reversed the direction of the engine or depending how you set on the track, the fan would change flow directions?
 

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Steam5.
The tender truck side frames are now made of metal and act as the pickups from the metal tender wheels. Should be a much stronger construction and the springy wipers have been eliminated.

JJ.
1. I don't really know. Bachmann considered it important enough to have a fan. Obviously to help cool the motor.

2. yes.

3. The fan is powered by the on board electronics with, I think, a polarised 12 volt supply. I never measured it.
It only works when there is enough volts going into the loco. It cannot be turned off.
Changing the loco direction makes no difference.
 

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In most cases, just having airflow helps the cooling. I would think that reversing the fan would still allow enough cooling.

Many people have done this.

Tony, one interesting thing about fans and airflow and cooling: for a given duct and fan, you will move more air with pressure than suction. This is one of the reasons you see the suction side larger in diameter than the pressure side. Physics does bear this out, and it is usually more a part of the equation than fighting convection air currents, which are very weak.

Regards, Greg
 

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Greg.
Undestood.
However, the fan is a fair way from the smoke unit and still manages to suck air down from the stack, so it must have a fair amount of suction.
In my opinion it is better for producing an efficient airflow, to assist the convection airflow rather than to fight it.
Especially as by doing so the smoke outflow is enhanced up the stack.
 

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Yep, as an engineer, I would think of it exactly the way you do. Working WITH the existing airflow is more elegant, engineering wise. In this case, you have to or forget your smoke unit.

Regards, Greg
 

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Discussion Starter · #14 ·
When I re-wire the loco (I currently plan to remove most of the electronics) I will remove the smoke unit, should I still keep the fan installed for cooling?

I’ll be adding a DCC decoder, how have others wired the fan up? parallel with the motor, or power it from DCC function output?

Oh metal trucks would be much nicer; I will have to track down a pair. The previous owner lost a couple of journal covers, so they need some work regardless.
 

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It might be more productive if you started another thread directed at the DCC experts, for assistance in rewiring the K-27 for DCC.
 
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