Large Scale Central

Front pilot is coming off track, need help!

Problem Solving
#1

I have no idea what this is happening … and… it just started happening! The front pilot is coming off the track and flopping to the side all of a sudden when coming out of the reverse loop onto the mainline. There is nothing on the track. I’ve increased the tension on the spring under the pilot. There is nothing visible that I can see that is causing this. I should add that the switches are spring loaded so the loco pushes the switch to the right directions on existing the loop and it springs back to the correct position to enter the loop after.

Here is a video showing it happen.

https://youtu.be/7pytD2P3g-4

Here it is again in slow motion.

https://youtu.be/LrNS3usYcO0

Any help or suggestions are greatly appreciated as I need this to be running again for Christmas day.

#2

You gotta throw the turnout. The pilot is too light to push the points over by themselves. If it did before, then something is jamming the points or the throw mechanism to keep it from moving freely.

#3

Todd Brody said:

You gotta throw the turnout. The pilot is too light to push the points over by themselves.

Have never had to do that before. The switches are spring loaded and set to enter the loop correctly. The loco pushes the switches to the correct position to exit and then springs back to the correct position to enter again.

#4

Look for grit under the throwbar. If it’s a new affliction, something has changed and dirt fits the bill, it doesn’t take much resistance to lift the wheels.

Windy days blows in silt, grit and stuff. Use graphite to lube the sliding plastic parts.

John

#5

Yes, when I start having that problem with my spring switches its usually dirt or debris. Also clean the sides of the rails where the flanges ride. If gunk builds up there the flanges can climb the rails.

Before every day’s run, I check my spring switches to make sure the points move freely and easily.

#6

Tim, look at the slo-mo video of the problem. At about the 13 second mark the pilot truck flange of the inside wheel rides up on the juncture between the curved stock rail and the switch point. From the look of the throw mechanism, it is a standard LGB. Try disconnecting the standard mechanism, and on the opposite side of the switch, hook a small rubber band to the throw bar with a substantial weight (something the rubber band will not move) on the other end of the rubber band and slowly stretch the rubber band until the loco will pass through the switch with out issue and the rubber band will still reset the switch to the main line position.

A bit of tinkering can’t hurt.

Bob C.

#7

Ok… I cleaned up the switch, all parts. Added a little graphite. It made it around 3 times and then did it again. Looking closer at the switch track on the far side (closest to the wall as it comes out of the loop) I noticed a sharp nick in the top and inside of the track. I just filed it more smooth and that may have done the trick. If the issue was indeed caused by that nick it sure is pretty small. I will post back later.

#8

It doesn’t take much sometimes.

#9

I use sprung switch track also. I need to clean them once in awhile as they can get stubborn. I have made it a point not to have any locos with lead or trailing trucks as these are particularly vulnerable to derailing at sprung switches.

#10

Ok… so it appears that by smoothing out the nick may have a done the trick. No more issues. If it was indeed that nick it really seems odd as it was not that big… It was indeed a rough spot but really not that big. The only other thing I can think of is that one of the pilot wheels is off kilter. And perhaps when it came around just right and hit that nick it would jump the pilot off the track. Dunno. Also not sure how to straighten out the wheel.

#11

Well, you could talk to TrainLi about getting a replacement wheel set.

#12

Check the gauge of the wheels and the gauge of the points. Derailments like that will happen if the track gauge is too narrow or the wheel gauge it too big.

#13

Here’s another solution - at least an analysis:

Push the engine to the turnout. At the starting point measure the base of the cow catcher to the track. Move the loco through slowly and note if the cow catcher is lifted up. My guess - and it is one- the turnout has dropped so that the front truck is lifted. Check the turnout for being level.

Wendell

#14

I doubt if the wheel set suddenly went bad, the nick in the rail may have added to the cause;

  1. dirt …under/around the throw bar and are the wheels clean? Where the rails slide?

  2. nick

  3. light weight of truck

  4. gauge

All these can affect tracking. But only dirt is variable and the nick a one time detail…

To test the wheel set roll it on a hard surface and see if the wheels are parallel to each other. You should be able to see any wobble.

I think it is still resistance to the throw bar from moving that is the main source of your problem. Remove the spring and test the engine through the switch making sure the wheels can move the points.

I make my own stiff leg springs and adjust them to just have enough force to hold the points tight against the stock rails…

John

#15

And here’s something else to wonder about: 4-driver locomotives with short wheelbases often hunt (nose side to side) a bit, one real life standard gauge type was said to do so “alarmingly”, - could that motion be making a difference?

Difficult to tell from video, how much clearance between pilot wheel and inboard side of cylinder is there as loco passes through curve?

What I’m imagining is a possible case of there being so little clearance that the hunting motion can sometimes cause cylinder to push against pilot wheels.

#16

Nope, its the pilot wheel on the inside of the curve that comes over the railhead. If it was contacting the cylinder, it would not travel further inboard to derail.

#17

What John and Todd said.

I know the “defense” is that it worked before. I submit it was working marginally, so any increase in friction or change in the loco’s “attitude” when entering the switch causes it to fail.

I’d add weight to the front pilot… increasing spring pressure might just lift the loco up instead of pushing the switch points aside.

Greg

#18

Greg Elmassian said:

What John and Todd said.

I know the “defense” is that it worked before. I submit it was working marginally, so any increase in friction or change in the loco’s “attitude” when entering the switch causes it to fail.

I’d add weight to the front pilot… increasing spring pressure might just lift the loco up instead of pushing the switch points aside.

Greg

Adding weight is the ticket. See George Schreyer’s page Big Hauler Tips #derailments

#19

I’ve never had much luck with lead weights on pilot trucks. You just can’t get enough weight in the space available to push through sprung switches. I’ve gone almost exclusively with some form of sprung downward pressure which uses the weight of the locomotive to keep the pilot truck in solid contact with the rails, similar to how a prototype locomotive’s pilot truck suspension works.

Problem is, some loco pilots aren’t designed like that, so it takes some re-engineering if you want some kind of spring arrangement to push down. I’m not sure about this loco, but I’d presume it to be similar to the LGB Mogul, whose front pilot is sprung by a spring in tension behind the pivot mount which pulls back to keep the truck centered under the pilot as it does up to provide some downward pressure. You can’t stretch the spring to provide more pressure as you can with a compression spring. If you want to use that spring to provide more downward pressure, you’ve got to trim the spring or replace it with a shorter one. That may give more downward pressure, but it also gives more pressure directing the truck back to the center, which on sharper curves may cause the truck to want to climb up over the outside rail. If you want to use some kind of spring in compression to apply pressure, you’ve got to re-engineer the suspension on the front pilot. On the loco in this example, there looks like there’s some clearance above the wheels to where you could put some weight there, but the pilot wheels are small, and I just don’t know how much weight you can fit in the space. Some stiff spring material screwed to the pilot arm and bent to contact the underside of the pilot deck would be how I’d attack it if I needed more downward pressure.

You’ve also got to be real careful with the spring on the switch. It doesn’t need to be too stiff. You need just enough pressure to hold the points against the stock rail, nothing more. It took a bit of work to get the springs on my return loop switches to have enough pressure to keep the points closed, but still easily allow the pilot wheels to push through without derailment.

Later,

K

#20

I agree, a single axle pilot truck doesn’t provide much space for weight. I did load down the 2 axle pilot truck on my 4-4-0 with lead shot and it really helped. I would try adding some weight to the truck if possible.

I would also investigate the switch machine spring to see if you can reduce its pressure on the points. I did that with the stock Aristo manual switch machines. I bent the spring a bit to reduce its pressure on the points.

I also shimmed the pivot point on my single axle pilot truck on my 2-4-2. By putting a brass sleeve on the pivot point, now the pilot truck can no longer twist on the pivot. So if one wheel is going to lift, both wheels have to lift, and with the weight of the wheels and a little added lead shot, the pilot truck doesn’t want to lift. But I made sure that my shim wasn’t so tight as to prevent the pilot truck from swiveling side to side.