I've found it's not unusual for Bachmann steam engines to come with the rods bent in a little bit, so they're creating a 'hitch' or even stopping the engine from running. I'd check that first - try the least difficult fixes first, then move on to the more invasive ones if they don't work.
TajuI have never had one of these apart. What does it take to do this? Do you repaire other peoples locos or just your own?
I posted a link before about this loco. Go take a look. It is torn down.
The link does not show the gear on the driver axle but you can post a picture of what you have when you get the drivers out.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
That definitely sounds like the original release of the K4 to me.
Randy's suggestion is also on point - of the two of these I have, one is out of commission with the buldging driver centers, which as he says is easy to resolve by simply removing them. More involved, but also possible, is to remove the valve gear and side rods, and pry the driver centers out without destroying them, sand them as necessary to make them fit, and re-glue them into the wheels.
I have a second of these that exhibits no outward problems, but still runs with a 'hitch'. There's nothing for it but to tear it down, check every part of the drivetrain, and put it back together piece by piece until I identify the offending part. I'm not sure how experienced with rebuilding locos you are, but I'd suggest that this isn't a particularly 'fun' one if you're inexperienced.
I always end posts about this model by advising you seek out the second and third versions of the Bachmann K4 - they're mechanically much improved from the original, and easily identified by the presence of a 6-wire connection between the tender and loco. I have three, all purchsed used, and they all run smoothly with a simple cleanup and lubrication.
I have repaired several of the original K-4's that locked up. Generally, I have found that the plastic driver center has bulged out; like the plastic expanded and grew. This jams against the rods. The fix for me is to carefully cut the inserts with an X-acto blade and extricate the pieces. This leaves you with a dished out driver. When finished you can re-paint the driver center flat black.
Just in case. The below link is for the newer version, DCC on board or DCC on board with sound. They might have come DCC ready with the DC adapter on the PC board in the tender.
There will be six wires between the loco and tender.
http://www.bachmanntrains.com/home-usa/dwg/dwgs/H844X-IS00.PDF
I will assume the HO an older version.
Below is a link to the one with no wires between the loco and tender. DC only.
http://www.tcsdcc.com/Customer_Content/Installation_Pictures/HO_Scale/Bachmann/K4_Pacific_4-6-2/bachman_n_scale_k4_pacific_4_6_2.htm
It is HO scale no wires between the tender and the loco. The bos is the one that has the large rendering of the loco on it. When it stops it locks up tight. I can move the wheels some and it will run again for a few inches. I use my finger to genlty get the wheels to move. I do not push down on it to free them up.
What does the box look like; is it a plain black box with gold "Spectrum" lettering, or an ornate black box with a large 3/4 view rendering of the loco on the front flap?
Is there an electrical connection between the loco and tender? Will the loco run (such as it can) by itself?
I'm asking these questions to determine which version of the Bachmann K4 you have. From your problem, I'm guessing it's likely you have the first generation release (fancy box, no wires between tender and loco). Unfortunately, this version has plastic driver axles that are prone to cracking with age (even without use) and allowing the drivers to become un-quartered.
This could cause the problem you're having, but it's not the only possibility - it will be much easier to offer advice when we can determine which release of the K4 you bought.
Welcome.
Is the loco DC or DCC?
It could be the rods. Are a couple rods locked up when it stops?
I am assuming HO scale. Bachmann makes an N scale also.
I hope you are not pressing on the loco to move the wheels a little.
I have a K-4 spectrum. When I try to run it it will move for a few inches and then lock up. If I move the wheels some with my hands it will run again for a few inches and then lock up. I purchised this unit at a train show and it had never been opened. Has anyone else ran into this problem?