Repairing Bachmann 2-8-0 valve gear

[Maletrain]

I took home another basket case loco from the club to repair it.

It is an N scale Bachmann 2-8-0, and the valve gear was jammed and the main rod (with the eccentric crank attached) was detached from the driver because the main pin had pulled out of its hole in that driver on the fireman's side.  The pin in the front driver on that side had also come out and was jammed in the crosshead.

I saw a slot like a screw head in the main pin, but was surprised to find that it is not actually a screw.  It is a pin that is solidly fastened to the eccentric crank.  That pin simply goes through the main rod and slides into the hole in the main driver.  Similarly, the pin in the front driver does not thread into that driver.

I managed to get the valve gear unjammed and the 2 pins back in place, so it now runs smoothly at slow speeds, forward and backward.

But, I am wondering if the problem is going to recur, since the pins do not seem to be retained in the holes, and have come out once (at least) already.

Because it is a club loco that was out of commission when I first saw it, I have no idea how it got into the state in which I found it.

So, I am looking for any advice on whether this problem is likely to recur once it has happened, and if there is something else I should do stop it from recurring.  It looks like I could put some sort of glue in the hole for the pin on the front driver, because the side rod just pivots around it, without the pin needing to move.  But the main pin seems to need to be able to rotate in its hole because it is solidly attached to the eccentric crank.  So, I can't glue that. 

[Sdynamo]

In my experience once the pins come out, they will do so again.  You might rough up the end of the pin a bit, and inside the hole on the driver.  Then use Loctite or a tiny bit of CA to secure it in place.

[randgust]

Well something isn't right.   The eccentric should have a rivet at the end allowing rotation of the radius rod on the end.  The eccentric on a model is usually in a fixed position, pointed 'generally' across the center of the drive opposite the pin.   I won't get into valve gear setting, but no, the main rod pin doesn't rotate in the hole.

If that radius rod connection is stuck that's what caused it.   What usually happens is it works loose, jams on the radius rod, and pops everything apart.

Notice the position of the eccentric in these photos:  http://www.spookshow.net/loco/spec280.html

Now, if that pin is slipping in the main rod it can be corrected:

1)   Crimp it slightly flattened and reinsert it in the hole (or)
2)   Needle in some thin ACC into the driver hole, tiny bit, but get it right, as it's not moving when you put it back in. (or)
3)   Try some of the Loctite that is OK with plastic, same thing, needle it in the hole, just a tiny bit, you have a bit of time before it sets up.

If you can't precisely control 2 and 3 and put 'too much' in the hole so that it forces back out, you'll glue the drive rods to the pin.  To help prevent that, a tiny bit of oil on the rod hole will prevent seizing, but again, don't overdo it.

[peteski]

Well something isn't right.   The eccentric should have a rivet at the end allowing rotation of the radius rod on the end.  The eccentric on a model is usually in a fixed position, pointed 'generally' across the center of the drive opposite the pin.   I won't get into valve gear setting, but no, the main rod pin doesn't rotate in the hole.

Exactly. Not sure why Steve thinks the eccentric and the main crank pin should rotate. the main crankpin and the attached eccentric are fixed to the driver, and on the real loco they are important part of the valve timing.  Here is an animation showing the motion.

[Maletrain]

OK, I am seeing that the main pin does not need to turn in its hole. I think my head is spinning right now, trying to work on 2 steam locos at the same time - and not spinning in sync with the 2-8-0 valve gear, apparently.

Anyway, the 2-8-0 valve gear does seem to be working properly with nothing jammed.  The main pin and the eccentric are shown as one piece in the parts drawing and that seems to be the case for both sides of 2 models that I have here to compare.

I did notice that one of the traction tires, which are on the same wheel  set, is loose.  I am wondering if this problem with the valve gear was caused by somebody previously trying to put on a traction tire. 

Which brings me to the question about how to do that.  Doesn't that require that I pull the main pin out of that wheel on each side to get tires off and on?

[peteski]

Yes, the crank pin will have to be pulled out so you can slip the traction tire onto the driver.
Kato Mikado has a clever design where the TT was on the rear driver which did not have crank pin. In most instances Kato's mechanical design is really impressive.