Left Turn Issue, MTH Mikado

I'm sure you checked that the traction tires are all seated correctly, nothing is stuck to any of them and none are twisted. Also that they all the drive wheels sit level on the track. This sounds like a problem I'd be coming to you for help John.

Is it possible the wheel gauge is a bit too wide (or narrow)? Compare the wheel gauge of the front drivers to that of the rear set.

Larry

Traction tires are in great shape, and it sits level on the track with all wheels on the track.  Wheel gauge is within about .005 between front and rear, and they compare to other locomotives that don't have issues on the same loop.

It's really odd, when I first got this, I tested it, and as luck would have it, it was making right turns and everything was fine.  I got it out because I was going to take it to the TCA Convention for our modular show, and it has this very bad habit, so it's probably not going to make the trip unless I can figure out what's going on.

I had a problem like this with a 0-4-0 dockside switcher.  The weight on the rear wheels was much less than the weight on the front wheels.  I added some lead weights to balance the engine and the problem was solved.  

I was also wondering about the gauge of the drivers.

If the loco doesn't turn with the track (maybe due to traction tires), it will force the wheel against the rail hard enough to make the wheel climb the rail.  You might try running with some of the traction tires removed.

It only has two traction tires.  I though of weight in the front, maybe I'll put stiffer springs in the trailing truck and see if the weight balance helps.  I don't know why turning left would be an issue, I see nothing that pushes it that way.

I was also thinking of a longer drawbar, though the 40mm looks good.

GRJ: Unusual for you to have a problem.  Are you sure that the wheel runs true, and doesn't have a bent axle or rim that causes wobble? If the axle were bent outside of the right frame bearing, the left wheel would still run true.  (I assume the right wheel is climbing the outside rail on the curve).

Running on my test blocks, the wheels appear to run very true, no hint of a wobble.  Correct, it's the right wheel that climbs the rail in the left turn.

There has to be a reason, but I'm coming up dry as to what it is.

Does the engine have  a lot of running on it?  Maybe the flanges are worn.

I have an older RailKing B-6 0-6-0 which had been running on Fastrack O-36 curves for so long that the flanges on the front drivers had worn to a sharp edge, and so the engine kept climbing the rails (sorry for the long sentence).  I ended up sending the drive block (just the frame and wheels) back to MTH for replacement ($50.00).  Now it runs fine again.

Stuart

You might try putting a little grease on the inside of the rail.  Years ago, there was a flange greaser on the Tehachapi Loop.  Last time I was there, it was gone.

The engine has 252 scale miles and 41 hours on it, so it's not worn out.  There isn't much sign of wear at all, hard to believe the flanges are worn enough to do this.

I don't think I can grease all the curves to solve the problem.

GRJ, is it on all left turns, or only in one or two locations?

It appears to derail on any left hand turn.  It doesn't do it every time, it's somewhat random, but every two or three turns, it's off the track.  Even when it doesn't derail, you can see it hopping up and then dropping back between the rails.

Did you try running it without the traction tires?  Did you try running it on a different radius of track?  When the loco is on a curve, can you move the front drivers side to side slightly?  Is there a gap between the flanges and the rails?  Did you try it on tubular track? Did you check the gauge of the drivers?  Are the traction tires on the left side?  

Are one of the rollers bent or not sprung properly, it could be causing a binding that causes the engine to lift off the track when in a curve or turnout.

Maybe it's not the loco.

Well it wont be running in NASCAR if it can't turn left

Since I don't intend to run it without traction tires, I see it somewhat pointless to take them off.  In any case, it should certainly run with them, and that's the problem I'd like to solve.  The object of the exercise is to get it running on O72, not to remove all O72 from the picture.  I can move the drivers a bit on curves and straight sections.  I don't have tubular track down to run it, and I don't intend to change track types to fix one locomotive, that hardly seems practical.  The driver are guaged properly, I checked them against other locomotives and the rear drivers.

Rollers are straight and true.

So, it's a couple of loops of Fastrack and a dozen turns?  The same track that many other locomotives run properly on?  I'd rate that as a long shot...

Correct, we'll be only running on "right wing" tracks.

 Run the loco in reverse and see if it still derails. Try running it with the side rods and valve gear disconnected to rule out any unseen binding or other issues.

Larry

I think Larry may have hit on your issue

I'm having the same problem with my Premier Angus, except mine hops over the rails when going through my 072 curves in reverse. When the engine was new (about a year ago) it didn't do this. Going forward it runs great. I have watched the front drivers articulate going through the curves and everything moves smoothly.

I have checked wheel gauge, traction tires, linkage for binding, and had the boiler off to see if anything underneath was causing the rear drivers to raise up and derail. I can find nothing. I contacted MTH about this and they want me to send it in. I would rather not risk shipping damage and pay a repair charge to fix something that has got to be fairly simple (if I can figure out what it is). I'm wondering if John and I have similar problems on two different locomotives?

Ken 

I guess it has to be a little clearer than that, what's the "issue" he hit on? 

Taking all the rods off leaves the locomotive inert.  The one of the blind drivers is the gear driven wheel, and they are about a paper width from the track, so the locomotive goes nowhere.  The two blind drivers don't always seat on the track, and other similar locomotives are built the same way with the blind drivers slightly smaller and/or higher.

I can see the locomotive slightly climbing as it run, oddly enough it's still the front wheel, but it didn't derail after a couple of trips around the loop.  On the bench with the shell off, I can't see anything in the rod linkage that would cause the issue.

I think I'm going to give it a run on the Atlas track on the club layout and see what it does there.

Could be Ken, why don't you fix yours and I'll see if it's the same issue!

My guess is that the traction tire is on the left wheel, and the traction tire on the rear driver is causing a clockwise torque on the loco.  In addition, the right side drivers have to slip when the loco goes around a curve.  The torque caused by the driver slip is adding to the torque caused by the traction tire.  This is enough to cause the right front drive to climb the outside rail.  To test this theory, you would have to remove the rear traction tire.  Now here is the test question:  Why does the loco work OK turning right?

I still say its wheel out of gauge John. I'm going to follow this topic. I want to find out what it is doing it. 

After more thought, I am sure the loco could use some weight on the front end.  The torque to slip the drivers as the loco goes around a curve has to come from the side force on the front wheel flanges.

I've measured every way from Sunday, I can't see anything out of gauge.  I've run it on the test stand, and there is no wobble of any kind, and I've measured diameter and gauging, all look good.

The additional weight on the front is something that I considered, but it would be pretty hard to get much there, it's kinda' full up front. 

I have little doubt that taking the traction tires off may fix it, but based on other locomotives, I wouldn't like the performance without the traction tires, so I'm not sure what that would prove that I already don't know.

I'll see what the run on Atlas track tells me, that might be interesting.

You certainly have stirred up many ideas.  Are your curves superelevated or reverse elevated by any chance? Or at the top or bottom of grades?  Are wheel bearings loose?  I'm sure you have checked the flange for burrs.  If you place loco on a perfectly flat straight track, any rocking on the drivers, front/back, side/side, or diagonally?

John, When you are trying to discover the cause of an effect, it is sometimes necessary to make modifications that are not permanent.  An easier thing to do would be to grease the top of the right rail and see if that stops the problem.  I don't like to suggest greasing the track, but that would prove the hypothesis in my last email.

If you remove a traction tire, you only need to remove the one on the left rear.

John, can you take the shell off and maybe get a better view of what is going on?

John Have you ruled out the tether? I have seen them torque the engine to one side or the other.

Pete

John will make shore your run on the inside loop so that you only go right.

 Haha.Harry!

Harry, that's exactly my plan for the show!

Pete, I did adjust the wires to the tether so there was minimal friction.  It was pretty stiff and I was sure I had found it, but after fixing that, same issue.

I've had the shell on and off a few times Steve.

I want to see what it'll do on the Atlas track and left turns, maybe that will tell me something I don't know.

John when I get a chance I will look at it we had some of those problems before 

 more with 3 rd rail stuff and brass.

Oh, I was planning on letting you see if you spotted something I haven't. 

John, perhaps you can take out the screws holding the rods to the front drivers, and let the rear drivers power the loco.

Larry

Also, can you take the main rods off and put them on a flat surface to see if they are slightly bowed, it may be that if they do have a bow in either one or both it may be putting more tension on one side only causing the axle to shift more to one side.

Are there any anomalies with the driver wheel flanges? Bumps, nicks, divots, warped spots, and the like.

Does it climb the rails if the front truck is removed?

John:

i have the same loco and have never noticed a problem on my layout.  You're welcome to bring your engine over to try on my layout and also to compare to mine.