R577 City of Nottingham loco wheels

[Ralphy51]

I’m having a problem with the large driving wheels seemingly locking . It’s a tender drive loco and so the wheels should be freewheeling but occasionally ( especially at low speeds) they stop rotating and so the tender is trying to push a static object .

I’ve lubricated everything and it seems free enough but definitely not as free running as say my R398 Scotsman. My other 04-06-02 locos have no problems .

Increasing speed seems to resolve but I suspect that whatever resistance is in play is still having an effect on performance .

Although it’s a vintage loco it’s never been heavily used and I’ve tried using a different tender but it’s still a problem.

Everything seems to be in order visually .

Anybody any suggestions please ?

[96RAF]

Check that the quartering is OK. This is where the wheels at one side are exactly 90 degrees offset from the wheels at the other side. If awry then a geometric lock can occur jamming the wheels.

[Ralphy51]

96RAF thanks for the prompt response . I’m not sure I fully understand that or how to check . Could you please elaborate ?

[Ralphy51]

Actually 96RAF I was being lazy and just checking out YouTube that seems to have a couple of videos .

[LTSR_NSE]

@Ralphy51 imagine the driving wheels as clock faces, on one side of loco rotate them until the screws holding the coupling rods are at 12 o’clock.

Holding the wheels to prevent them rotating look at the wheels on the other side of the loco - they need to be at 3 or 9 o’clock.

If they are different from this then that is why they are jamming.

Alternatively if the coupling rods (or valve gear) are at all bent or buckled this can also cause jamming.

[Ralphy51]

I’ve checked now and the “weights” on the driving wheels are all aligned on each side and pretty much 90deg aligned, one side as compared to the other .

[Topcat2018]

There was recently a discussion on the saem topic but I can't seem to find it. Maybe someone else can. A common problem with locos that have Walschaerts valve gear is that some of the rods in the valve gear can jam. I don't know the exact configuration on your loco but check that the valve gear rod connected to the return crank (that's the one on the centre wheel) is not fouling on the nut that attaches the crank to the wheel. Also that the connecting rod from the centre wheel to the piston rod is not jamming on the piston slide, and the two little rods connected in front of the back end of the piston rod are not jamming on anything.

[LTSR_NSE]

The next thing to check is to gently rotate the wheels (through several full 360° rotations) and observe/feel if there are any places where you encounter resistance or jamming.

If you do, look closely at the coupling rods and valve gear on both sides to see what is catching/binding/jamming together.

[ColinB]

This is the reason I hate tender driven locos, when my one did the same it took ages to find it. Check the cylinder block, the piece of plastic at the front which the valve gear ends fit into, on a real loco it is where the pistons are. On mine over the years it had split where it clips onto the chassis causing it to move and lock the valve gear every so often. They are made of plastic and because they clip onto the chassis with these models, it is easy for the plastic around the clip area to become brittle with age and snap.

[Topcat2018]

@ ColinB

I have to disagree. I don't think there is a fundamental problem with tender-drive locos per se. Most of my locos that have a tender are tender-driven (over 60) and I've rarely had a jamming problem. Loco-drive locos can have the same problem and it's actually worse because:

1. You can burn out the motor because it's stalled by the jam.
2. The motor holds the jam in position so it's more difficult to free.
3. It's easier to fault-find a jam in a tender-drive loco because you can turn the wheels and run it along the track by hand.

The worst that can happen with a tender-drive loco is that it slides round the track.

[atom3624]

A few photos could help - may take a few hours to get authorised.

I'd be interested in the suggestion of gently rolling the wheels with the locomotive in your hand, to feel for tight spots.

My guess is possibly the slider of the piston is misaligned, the valvegear has even been removed and replaced incorrectly and / or the coupling / connecting rod screws are loosened.

At an extreme there could be some fluff, dirt, cat/dog hairs trapped, or a touch of light machine oil is required.

Can you easily move each axle / wheel pair side-to-side?

Al.

[Simmo009]

Had one of these recently. Check the axle pathways would be my first thought, clean and lube. But this did not resolve the issue. Disconnected the rods and individually tried the axles free rolling. Then I swapped the front and rear axles to check there wasn't a problem with the axles. Remember to keep the orientation correct. Eventually, having identified the front driver was the problem area, it seemed the isolator between the wheel and axle was binding on the chassis block. Opening the wheel back to back by 0.1mm got it all running well. Not ruling any of the above suggestions out, but there could be several areas to check through. This was on a Princess, not radically different from what you have.