4-6-0s

[ebtbob]

Good Evening All,

      I have two of the 4-6-0s and both have the same maledy.   Going downhill,  they surge.   Is there anything that can be done to correct this?  I had a friend who thought he had a fix for this problem but it did not work.

[Jim Banner]

Going down hill, the motor may be driving the train or the train may be driving the motor, depending on the steepness of the grade and the rolling resistance of the train.  At certain speeds, the train may shift back and forth between the two conditions, causing surging.  Generally, when the motor is driving the train, there is little friction in the motor and in the worm and pinion, so the train tends to speed up.  When it gets going fast enough, the train is outrunning the motor and so tries to force it to go faster.  But the power flow is then from the pinion to the worm which causes excess friction in the worm and pinion and shifts the worm longitudinally and the motor shaft along with it.  In some (not all) motors this end force can cause binding.  So now the binding and the gear friction slow the train down until once again the motor can drive the train, reducing the friction, and letting the train speed up again.

If this is the source of your surging, minimizing end play in the motor, usually by taking the motor apart and adding a washer or washers to all but eliminate end play, and cleaning and greasing the worm and pinion can make a big improvement.

There can be other causes of surging.  If you are running on DCC and have a decoder with BEMF control, you may get the similar surging if the motor is trying too hard to control the speed.  The solution there is to back off on the BEMF a bit or just turn it off.

I too have a pair of 4-6-0's but have no surging problem with mine in spite of running them up and down a helix with an almost 4% grade and a diameter of only 3 feet.  I usually add a trace of very light "conductive" oil to my rails after cleaning them which limits my passenger train to three cars (4 on a good day) but may also reduces surging by allowing a bit of wheel slip rather than binding when the train switches from being driven by the motor to driving the motor.  From experience with my H0 layout which also has lots of grades, surging seems to be worse when the rails and wheels are absolutely clean and dry, and is worst with locomotives fitted with traction tires.  This to me supports the idea that a bit of wheel slip acts as a safety valve to help prevent surging.

I would be interested to know what the fix was that you already tried.

Jim

[ebtbob]

Jim,

        Thanks for the ideas.   The idea already tried was simply running the engines everyday for several days.   My friend that method solved his surging problem but it did not work for me.   On the other hand,  I know,  for sure,  my engines are definitely broken in and except for down hill,  they run very nicely.

[JerryB]

Barry's Big Trains manufactures a replacement chassis for the Big Haulers. See:

http://www.barrysbigtrains.com/

His replacement power train really solves all running problems with these well detailed locomotives, including the surging. It turns Bachmann's great, low cost engine into a long life, very high performance locomotive.

Happy RRing,

Jerry

[darryl1936]

Barry's Big Trains manufactures a replacement chassis for the Big Haulers. See:

http://www.barrysbigtrains.com/

His replacement power train really solves all running problems with these well detailed locomotives, including the surging. It turns Bachmann's great, low cost engine into a long life, very high performance locomotive.

Happy RRing,

Jerry


Not for On30 !!!

[JerryB]

Of course NOT! I apologize for creating confusion!!

That will teach me to try to surf my favorite RR websites while I'm printing the output for a major project. Too much going on at once on the desk.

Happy RRing,

Jerry