Bachmann 'jerky' running. Hope there is help out there.

[A4 Terrier]

I have added a decoder to a Bachmann Standard class 5MT.  When testing it was found to have something ' 'catching' in the running mechanism.  At the same point in each driving wheel rotation it would jerk or on a very low speed setting, stop.  Checked all the steam motion to ensure there was nothing jamming. Took the motor out to examine the gearing but could not see anything obvious.  Disconnected the steam motion so that only the coupling rods remained and found the fault still existed.  It appears to be related in some way to the leading drive axle which at the point of the issue, is tight.  Removed the wheel set and checked gauge with a back-to-back,  Removed the compensator and regreased. Reassembled the loco and it remains the same with an interrupted rotation of the drivers.  If it is given enough speed it is less noticeable but this is not the answer for smooth running at all speeds.

Hope someone has experienced and resolved the same problem or can help me to get this right.

Thanks,

[Combe Martin]

Have you checked the wheel quartering ?

[34theletterbetweenB&D]

3 hours ago, A4 Terrier said:

...At the same point in each driving wheel rotation it would jerk or on a very low speed setting, stop...

This is the crucial piece of information. Because the jerk or stoppage happens in the same place on every rotation of the wheel set it has to be on the wheelsets or coupling rods, 'somewhere' given that the outside motion has been removed. Bends in, or incorrect length of a coupling rod, damage to the crankpins, damage to the axle gear, fixed components snagging on the wheel (pick up wiper on the wheelback for example) are further possibilities, producing equivalent results to a wheelset out of quarter.

 

And just in case this is a new purchase. Was the model showing the problem before a decoder was fitted? If so a return to retailer is indicated.

 

3 hours ago, A4 Terrier said:

I have added a decoder to a Bachmann Standard class 5MT.  When testing it was found to have something ' 'catching' in the running mechanism...

On reading those first two lines I immediately thought the speedo drive representation was the likely bfault, as if this is slightly out of position it runs like a three legged dog. But as you have had all the motion off and it goes tight on the front driver that can be ruled out...

[Quadrille]

No drive system should bind or catch.   If you think that it's the 1st axle then remove it and check to see if the click persists by rotating the other two axles.   You have checked the B2B but have you checked the backs of the wheels ?     If the body has been removed then has it been replaced correctly and does it align properly ?

[DCB]

My first question would be did it run better before fitting the de coder and  if so how much was dismantled  for the fitting.  I have a std 5 somewhere, its too slow for passenger work and struggles to pull the skin off a milky Latte on freight but it runs smoothly enough.  I can't remember if it is split chassis but if it is the split chassis halves can get out of square.   The leading or another wheelset may not be symmetrical for crank throws  so was it put back as it came out.
It does not sound like  the crank pin is hitting  the connecting rod but that is a common failing if the rod is bent or the spacers are put back wrong.    On a wiper pick up  non split axle chassis the wiper hitting the wheel balance weight or something else on the wheel back.

[peterfgf]

I would strongly suspect a cracked gearwheel.  These cracks are radial, propagating form the centre, and are difficult to see with naked eye.

Having said that, I've just taken apart a Hornby 5MT which I suspected had the same problem (same as my Rebuilt Patriot).  I couldn't see any cracks but I did clear out an excess of stiff grease.  Loco runs fine now. 

Going off a tangent. I can't understand why manufacturers use grease to lubricate gears.  Prototype gears, for example marine gearboxes, are lubricated by oil and only a thin film of oil (microns) is needed to separate the teeth.  Grease is handy on exposed machinery  or non-tight oil boxes but not in this type of gearing.

[Combe Martin]

The Std class 5 wasn't produced with a split chassis, that was the Std class 4 before it was replaced with a 'conventional' chassis.  Also the Std class 5 has the gear drive on the centre axle but the problem is said to be the leading driving wheel axle so it's not a gear problem.

[peterm1]

I've had this problem more than once with quartering. Living in Australia, I tend to sort things out for myself, so I bought the NWSL quartering jig. When this happens and I track down which wheel it is ,I correct that one and see how it goes. Any tightness, and the others are fixed.

 

I think you'd be surprised at how often this happens, particularly with the price of this stuff.