Airfix loco problem

[LMSmike]

I have a tender drive Airfix loco which runs erratically. Very jerky. Lift the tender off the rails and it runs fine. All electrical connections, pick-ups, etc. checked OK. Sometimes runs well in one direction.

Any suggestions, please?

Mike.

[Colin]

If it runs OK when there's no load on the powered axles, perhaps the problem could be with the gears. Airfix mechs are pretty long in the tooth now and you could have some badly worn plastic gears which can either de-mesh or jam from time to time, especially if due to wear they're too sloppy on their axles and have excessive sideplay as well.

[Guest stuartp]

Pretty sure my Airfix Scot chassis was a plastic job with (horribly cheap and nasty) springy brass pick-ups, not split-chassis like Mainline. I'm also fairly sure all the tender wheels were plastic with no pick ups at all. As Colin said, they're getting on a bit and they weren't all that great when new. If it runs fine with no load then my guess is you've shed a tooth somewhere and it's jerking as the drive to one axle slips and the other takes all the load.

 

Good news is the gears are asy enough to get out, if you get one second hand as spares or repair you can often make one good drive train out of two duff ones.

[brossard]

I'm pretty sure that replacement motors are produced for these (IMHO) quite dreadful motors, for example:

 

"http://www.intercitymodels.com/Lima01.html"

 

A more drastic solution is of course to do a brass chassis and proper gearbox. I have an Airfix 4F which I plan to do this to - I better get a move on before Bachmann or Hornby announce an updated RTR model.

 

Then, again, unless there is a strong emotional attachment to the loco (you don't say which one), why not bin the thing and get a new one? Split chassis are difficult (but not impossible) to convert to DCC.

 

John

[BR60103]

My Airfix Scot never worked well. I eventually found that the wires from the loco (pickup) to the tender (motor) were defective - internal broken. Replacing these made it work.

[Simon G]

I have an Airfix Scot which had the same issues with jerky running - take it off the track and it was fine. If the jerky running is associated with points, crossovers, tight bends etc, it is almost certainly a pickup issue, and not a slipping or broken gear. My Scot is like Stuartp says - pickups from the loco and not from the tender, which has plastic wheels. I also have an Airfix 4F, which also only picks up from the loco wheels and not from the tender wheels.

 

Like BR60103, I replaced the wires from the loco pickups to the tender, which improved things a bit. I also made sure that the pickups were as clean as possible, as they are prone to picking up fluff etc. The other thing that I checked and adjusted were the back-to-backs on the 3 loco axles picking up the current - there should be a distance of about 14.2 mm between the insides of the wheels - if they are significantly more or less, this can affect the power pickup (as well as the smooth running over the points/crossovers etc).

 

I think that it is worth a bit of effort to sort these Airifx locos, as when they are OK, they do run quite nicely (not as good as current Hornby/Bachmann models), and are capable of very controlled slow running, albeit a bit noisily.

 

Simon

[Guest stuartp]

... I think that it is worth a bit of effort to sort these Airifx locos ...

 

Indeed. Bachmann Scot chassis (and a razor saw to the body to make it fit) and a Mainline/Bachmann tender. Sorted.

[LMSmike]

Thanks for all the replies. I got my locos mixed up! It is a Scot which is giving the problem. In theory it's new (old stock) and the gears looksound. Next step is to run leads direct to the tender to eliminate any pick up problems.

Thanks again.

Mike.

[Simon G]

Mike, if I am right the Scot should already have a lead direct from the loco to the tender (But I cant check just now as I am work!). As it is nearly new, albeit about 30 years old, there is the chance of slight corrosion on the inner sides of the wheels, and on the brass pickups, where they come into contact with the wheels. It will be obvious on the brass as you get a greenish copper oxide on the surface. What I would do here is to lightly clean up the brass pickups and wheels with a fine emery paper/cloth to remove any surface corrosion or general muck. For the wheels check both where the brass pickup comes into contact, and also the wheel rim which contacts the rails. A little muck here can affect the loco running.

 

Simon

[LMSmike]

Thanks again for the advice. The loco is now running very well! More dismantling showed several faults.

Pick ups out of line and binding on the wheel rims, still making good contact but stopping free running.

Some dirt on the contact point of the pick ups.

Too much pressure on the front bogie, which takes weight off the front drivers.

Wires to tender trapped under the weight block (but I don't think this actually caused a problem, other than restricting the amount of slack wire).

I suspect this is a loco which will want regular check ups for pick up position and cleanliness but I'm still very pleased with the result.

Mike.

[Horsetan]

Indeed. Bachmann Scot chassis (and a razor saw to the body to make it fit) and a Mainline/Bachmann tender. Sorted.

 

 

 

...or a new Hornby Reb. Scot/Patriot chassis?