Generic Hornby 0-6-0 running issue

[GWR-fan]

I purchased a new Hornby generic 0-6-0 chassis and placed it under an older Hornby LMS?Midland "Jinty" body (a pity as the original chassis from 1986 ran superbly).   The running in the forward direction is impeccable with the slowest of smooth crawl,  however, in reverse the loco behaves as if it has a quartering issue.  As speed increases the issue is masked,  however, at low speed the loco jerks with each rotation.  If it was a quartering issue then the forward direction would be impacted as well.

 

I am wondering if the problem may be related to the worm position.

 

Edit:  I had thought that possibly the armature shaft was moving with direction change, causing the worm relative position to the axle drive gear to change,  however,  the shaft did not move at all.

Edited Monday at 01:02 by GWR-fan
Additional information

[34theletterbetweenB&D]

Further possibilities - such as a pick up wiper snagging on a wheelback, side rod catching on fixed structure - which only occur in one direction might account for this.

[Artless Bodger]

Is this a chassis with traction tyres on the middle set and a sprung rear axle? I've had no end of issues with some given me by a relative, 2721 and J83. When running backwards the sprung axle tends to rock - I've seen it with the chassis on a rolling road. The best I've managed is to remove the springs and traction tyres, which means the loco sits down firmly on the back axle, it almost converts the chassis back to the original Triang chassis style - effectively a jackshaft 0-4-0. Caveat - it still does not match my Bachmann 8750 for smooth running. I had similar problems years ago with a Fowler 4P tank.

[GWR-fan]

Thankyou for suggestions.  Wipers and rods are clear of obstructions.  The chassis is the later type without traction tyre and has a fixed rear axle.  It is a pity because from experience these chassis can be tempermental in so far as smooth running (power pickup),  as this model runs so well in the forward direction with extremely slow crawl and smoothness (a pity it will not run well backwards).

[philsandy]

 

If it's only a slight jerk in one direction it could still be a quartering issue. I've had a couple of locos do this after converting them to EM. The slightest of adustment to one of the wheels rectified the problem. 

[The Johnster]

Try a 'deep clean'; remove the keeper plate (carefully so as not to put stress on the motor feed leads), and drop the wheels out.  Clean the wheels and the chassis block with rattlecan spray electrical switch cleaner, which should be powerful enough to blast most of the crud away including the coloured grease factory lube, then scrub any remaining with an old toothbrush.  Leave it overnight for the cleaner to vape off, and very carefully relube all the points in the manual sheet, using a suitable non-mineral light machine oil (your local model shop, not neccessarily railway, will have this) applied with a syringe, or a drop of lube on the end of a pin if you haven't got a syringe to hand.  The name of the game is extreme parsimony with the lube, as little as you can get away with. 

 

Then re-assemble and test-run the chassis.  If all is well, replace the bodyshell and... enjoy!

 

 

 

[33C]

If it has the split rods, are they on the right sides? Plus, the holes may have no free play and/or burrs from the stamping process. A light brush with a file could work wonders.