Advice on jerky running

I'd be very surprised if you had really managed to alter the quartering; that usually takes some force, and you'd certainly notice you were doing it unless the wheels are loose on the axles, which would be a manufacturing fault.

Other possibilities include (i) general binding - at the 'tight spot' does every axle have a reasonable amount of side-play, or is one of them binding, perhaps caused by a mis-aligned keeper-plate or a bit of flash on the back of a wheel catching something; (ii) muck in the teeth of one of the gear wheels (I don't know the details of the drive-train on this loco); (iii) slightly dodgy pick-ups or muck on the wheels preventing reliable pick-up - this can imitate binding astonishingly convincingly; (iv) wheels removed and not returned in exactly the same place - perhaps accidentally swapping them from one side to the other of the loco while you were working on it. There are many other possibilities which could cause this problem, and no doubt other people will have their own suggestions.

The classic way of finding out if the binding really is caused by a quartering / coupling rod problem is to remove the motor - or whatever it is in the drive-train that prevents the chassis free-wheeling - and then pushing the motorless chassis along on a piece of paper to see if the binding still exists. If it does, then you'll know where the problem is, which is the first stage to fixing it.

Of course, if the bind is only slight you could always use a feedback-enabled chip to smooth it out ;-)

John

Thanks for the response. The J39 is one of the old split chassis locos, so there are no pickups. The decoder I've used is a Lenz Gold, so that has feedback enabled, but the binding problem is still there.. :(

I will have to examine the whole drive train and see what I can discover...

Ian J.

In my experience those split chassis locos vary between running very well and running very badly - I've seen manyinstances of each. I'd feel inclined to run a wire direct to each motor brush to see how it works then; if there is 'real' binding rather than a pickup glitch, this will show it - then, as you say, look through the drive-train to see if there's any grit in the teeth of any of the gears.

John

"L42" wrote

It's almost certainly a problem caused by the motor & decoder not being compatible. It's possible with the Gold to change the settings to suit different types of motor. I can't remember the CV you need to adjust, but read the manual which came with the decoder and the solution will be in there.

I had a similar problem with a Bachmann K3.

John.

Are you sure? when I tested the motor before attaching it to the chassis it seemed absolutely fine, and the problem of the jerkyiness only happens at one point, the same point in the revolution of the wheels...

Ian J.

"Ian J." wrote

Of course I can't be absolutely sure, but the symptoms sound exactly the same as those with my K3. I t ran fine of DC but didn't like the Gold decoder I fitted, until I tweaked the 'motor type' settings.

You've nothing to lose anyway even if that is not the cause, all you do to put things back to where they were is to reset factory settings on the decoder (write '33' to CV8).

John.

I don't seem to be able to find any advice on which motor type setting to use with which motor, any ideas on which settings go with which motor types?

Ian J.

Iassume this is an 6 coupled loco. To illiminate the possibility of a motor / gear train/decoder problem -- remove the coupling rods and run it on the straight and level. If all is well then the problem is in the quartering/coupling.

Hi all,

Many thanks for the replies so far. I have disassembled the loco again, checked the gear train for any bits of dirt that might have been causing trouble, but found nothing. It does seem as if the centre wheels don't run quite true, wobbling slightly, however when I put the loco back together it did seem to perform better, if not as before. So it might be a combination of a slightly poor running that didn't show with conventional DC, and the addition of the decoder. I have yet to try out the different motor settings to see what effect they have, I will post back once I have tried them.

Ian J.

Good luck, and do let us know how you get on!

Is the centre axle on this model fixed, or is it sprung as on some Bachmann models? If so, could this be puhsing the axle out of alignment?

John

Ian,

Wobbling wheels can be a sign of quartering being off - i.e. the coupling rods force the axles out of normal alignment to accommodate the errors in quartering.

Jim.

"Ian J." wrote

Just experiment and see what happens.

John.

Well, I've tested the J39 with various motor settings, it seems to like bits

1 and 2 (0 and 1) (decimal 3) being set best, though it wasn't much of a difference between them all really.

Btw, for John (caronprom) the J39 is a solid chassis 0-6-0, no springing whatsoever...

Ian J.

Until I got one of those snazzy guage tools from Mainly Trains I frequently set wheels slightly out of paralllel when adjusting the B2B - result of levering one side out then the other, but differing amounts. This often resulted in wobbly wheels and somewhat jerky running.

Worth a check. Cheers, Simon

(Snipped)

Let's be clear here - you haven't taken the wheels of the axles at all, you've just removed the wheels and their axles from the chassis after taking off the keeper-plate? If that's all you've done I can't see how it could possibly affect the quartering - if it was out to begin with, then that's a manufacturing error, but I'm supposing that you'd have seen that to begin with, and anyway since you've been tinkering with the loco I suppose that they won't accept responsibility.

Next question - is it possible to do anything that will enable the chassis to 'free-wheel' (Lifting or removing the motor for instance?

John

Yes, I did that and it free-wheeled more or less ok. I think there might be an alignment problem in the gears though as they do seem to 'hunt' while being turned by the motor, and that has an effect on the geared axle.

Ian J.

Dont know about that, gears do that anyway. Be more concerned that more or less ok free wheeling translates to jerky when coupled. Did you check the back to back all round the circumferance ?

Simon

If the chassis freewheels with no binding - hold it firmly down on a pad of paper while pushing it along to make sure that the wheels are turning properly, or run it down a slope - then you can be pretty sure that the quartering is fine, so don't mess with it!

As suggested, the gears may 'hunt' a little anyway - are they all turning smoothly and without resistance?

John

I didn't test without the coupling rods, so the freewheeling was with all the wheels coupled anyway.

Ian J.