I recently got a BLI SW7 in HO scale. This is my first DCC locomotive and I am very happy with the detail. However, I am running into an issue that when I drive it forwards through the diverging branch of a turnout either direction (leaving or joining the main line), 99% of the time the front axle of the front truck will lift up and fall over the rail. There are a couple turnouts on my layout that if I take extremely slowly it makes it through sometimes. It will go through turnouts backswards all day with no issues.
I am using atlas code 100 remote snap switch turnouts. I do not believe the issue is in my trackwork. My track laying skills are far from perfect, but the joints seem pretty level and tangent. My other locomotives and all my rolling stock make it through the turnouts with no issues at much higher speeds. I also just took this one to a train show when my club displayed our layout, and I experienced the same issues.
At first, I thought the problem was wheel gauge, but I checked with a NMRA standards gauge and they are pretty spot on. Nothing seems to be restricting the trucks ability to rotate. It is able to turn freely enough that it is limited by the stairs at the front of the engine.
I think the problem is the way the front truck pivots up and down. The pivot point seems to be a little back, above the second axel instead of above the midpoint of the truck. This causes most of the weight to go into the second axle, and the engine is alread a little heavy towards the back end. The front truck seems very prone to lifting the front instead of turning. It seems that when the locomotive goes through a turnout and the front wheels are pushed against the rails, instead of turning, the front wheels have an easier time lifting so the just go up, ride on top of the rail, then fall off the other side. I should note that it does not have this problem when going around a normal 18 inch radius curve, it handles that perfectly fine.
Let me ask you for some clarification. When you say “either direction”, do you mean that you are physically turning the loco around so that the rear truck becomes the front truck as it runs through the turnout?
Sounds to Me that You may have a pinched wire from the truck to the frame preventing the truck from pivoting fully, up/down side to side movement. I have an older BLI SW7 that did exactly the same thing. Wire was caught in the frame making the wire shorter restricting the trucks pivot.
I had the same problem with a Proto 2000 PA. It could be the cause of the OP’s problem. I hope that he will respond to my prior question on the direction of the loco so that we can understand if it is one or both trucks.
I don’t own one of these, but the first thing I would do is put the loco on a flat surface, such as a piece of glass, and check if all wheels are sitting on the surface. If they don’t, I would put the loco on its back, and check the wheels/axles to see if they are sitting correctly on the truck. If the wheels look OK, I would dismantle the engine and see what’s going on. It could be a wire, as suggested above, or something else preventing the truck from pivoting correctly in all directions. A warped frame or truck could also be causing problems.
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The snap switches have plastic frogs that can be taller than the surrounding rails.
A way to check this is to take a straight edge place it on the frog and see if there is a gap between it and the rail head. (If you are using a metal straight edge remember to turn off the power.)
If you find a frog that is taller than the surrounding rails you can use a fine grit sharpening stone to file down the plastic, without damaging the rails.
Other suggestions about the truck swing is also a possibility- -definitely something to check.
You did not mention if the locomotive is pulling or shoving cars through the diverging track of the turnout.
As a newbie, the OP is subject to moderation, so he and we are at a disadvantage while we wait for his response to our replies.
Here is what we know so far:
The front truck pivots up and down as it moves forward through the divergent side of a turnout.
The loco will go through turnouts backwards (in reverse?) without derailing.
He is using Atlas Code 100 snap switch turnouts.
All of his other locomotives (and rolling stock) make it through the turnouts with no issues and at higher speeds.
He experienced the same issues with this loco on his club layout.
There are a couple of turnouts that the loco makes it through sometimes if it is moving at an extremely slow speed.
He does not experience this problem when the loco goes around 18" radius curves.
In my experience, whenever a loco derails on a turnout, a locomotive usually exhibits a problem before it reaches a turnout, typically on a curve somewhere before the turnout. If the curve causes the problem, it is either because the curve is too tight, kinked, or one rail is higher or lower than the other. Just a suggestion, but I would look closely at the peformance of the truck on the curve that precedes the turnout.
Check the wheel gauge on all axles. Check for swivel of each truck for symmetry…they swing in arc fully in both directions, no binding. As mentioned, do all wheels make contact with a shiny flat surface when the locomotive is placed on the surface? Might be an incorrectly inserted axle end or a warped truck.
The correct way to test the trucks/wheels would be to set it on a sheet of glass or mirror and take a sheet/piece of looseleaf writing paper and try to slide it under all the wheel flanges touching the glass…if You can do this to some of the wheels, That wheel is part of the problem…You should NOT be able to slide the paper under ANY wheels.
Sorry that is a bit confusing. If the locomotive is going in reverse (Rear truck first) It will always make it through fine. By either direction, I mean that when the locomotive goes fowards through a turn out it will derail wether it is traveling from the main route to the branching path or from the branching path to the main route.
Thank you all for the advice. I am trying to work through several of the fixes offered here. I will try to respond to all the suggestions.
When I say it will derail going either direction, I mean that when it is going forwards (front truck first) it will derail both going from the main route to the branch and going from the branch onto the main route. It will not derail if it goes reverse through the turnout (rear truck first)
I will try to check the pinched wire problem. This is something BLI support recommended too. I am able to turn the truck by hand without interference until it physically hits the chassis, but I still intend to check. I just have to figure out how to get the shell off. There are some handrails that attach to both the chassis and the shell so I am not sure how to tak the shell off with those in the way. I have asked BLI support for instructions.
I put the locomotive on a flat surface and ran paper under the wheels. I assume when you say it shouldn’t slide under, you mean it should go in freely with no force? I could get it under all the wheels if I pushed a little bit. No wheel would let it slide in freely, but the front axel wheels would give with less force than the others.
I have checked the wheel gauge on all axels and they are all good.
I tested the flatness of the plastic frogs compared to the surrounding rails. It seemed like they were pretty even. The frogs are ever so slightly higher than the rail, the straight edge seemed to have a small gap between it and the rails, but so slight paper probably couldn’t even make it through. Could this height still cause a potential problem?
OK, thanks for those replies. What I am trying to do is to isolate the problem to one truck, the front truck. So, if you were to physically pick up the locomotive and turn it around and run it forward so that the rear truck reaches the turnout first, does the loco derail on that rear truck?
I am running into an issue that when I drive it forwards through the diverging branch of a turnout either direction (leaving or joining the main line), 99% of the time the front axle of the front truck will lift up and fall over the rail. There are a couple turnouts on my layout that if I take extremely slowly it makes it through sometimes. It will go through turnouts backswards all day with no issues.
Let me ask you for some clarification. When you say “either direction”, do you mean that you are physically turning the loco around so that the rear truck becomes the front truck as it runs through the turnout?
Rich
Sorry that is a bit confusing. If the locomotive is going in reverse (Rear truck first) It will always make it through fine. By either direction, I mean that when the locomotive goes fowards through a turn out it will derail wether it is traveling from the main route to the branching path or from the branching path to the main route.
Andrew268
When I say it will derail going either direction, I mean that when it is going forwards (front truck first) it will derail both going from the main route to the branch and going from the branch onto the main route. It will not derail if it goes reverse through the turnout (rear truck
Had trouble with another model of theirs, found out that their connection point for the body to the truck was off by a smidge and that was enough to vere it off some turnouts like Shinohara.
Let Me say this one more time…You should NOT, be able to stick the paper under ANY wheels. If You can, that is the wheel or truck that is floating on the track and barely touching the track with any weight on it making it easy to follow any dips or kinks in the track leading to derail…
It has been awhile but I tested it alot and found a lot of others online that had the same issue. I ended up selling it rather than messing with it and maybe failing at repair.
