FLakey Williams Coupler

A lot of older Williams diesel engines have that problem with the coupler. It's the coupler design, and one thing that will fix it is to use a tie wrap or rubber band to hold it closed.  Put the tie wrap over the movable part(the arm) of the coupler assembly but make sure the knuckle coupler area is clear.

FYI, I have a few older Williams engines, all my Williams engines are from before Bachmann buyout of Williams.

Lee Fritz

Before we go wrapping and/or glueing things, there is a procedure involving only a

pair of pliers and common sense. It has worked 90% of the time for me on lazy manual

couplers (brand not important).

This true fix is seldom mentioned here, and I don't know why. It is not usable on the latest

(and unfortunate) O-gauge coupler designs, which, if they won't stay shut, pretty much

need to be thrown away. But that's another story.

The knuckle pin is held up and in the knuckle slot by a sprung or springy armature. Sometimes the spring or armature is not robust. Using a pair of needle nose pliers,

grasp the armature near its base, and, supporting and "protecting" the actual base 

with your other hand/finger, gently bend the armature upwards a FEW degrees and see

if it doesn't snug up a bit better.

This works on metal and plastic.

It's not a new idea, at all.

Be patient; learn the equipment.

It has solved, actually, most of my problems with the opening manual coupler.

There are faulty parts and assembly, which this cannot fix, but start here.

Much cooler and more manly than a twist-tie. 

Hello D500

That works for me too. 

Tiffany

 While tweaking operation is the likely answer, bad track joints could be another reason too. I've had them become slightly magnetic as the power got drawn through a bad tubular track pin connection. That area collecting metal dust & me feeling heat there, made it obvious.

  Don't those have a real low hanging "tack"?

And a stiff pin arm with a spring?(bounce?)

Those can be re-sprung at the cost of closing pressure being higher.

 It is custom tuning work (disassembly), but "massaging" the knuckles pin ramping could cure that pressure bit. 

When pin tweaking, the knuckle pin should be at a plumb position, or leaning to the truck slightly when closed. Check the pin is smooth at the tip, not grabbing and walking down. It "blocks", it shouldn't "grab".

"Walking" open, or lack of a full close, is the issue that usually fixes.

Try to bend the arm, not the pin. Or you might round out the hole, loosen the press, or ruin the pin flare. Loose pins are an issue.

On brittle tempered metal bending the pin may be all you can do with base tools. And you just might shatter either without care.

The number of re-bends on those is... "you got lucky already" 

Tuning(vs a tweak) couplers requires the "right" parts. And I don't mean a part number.

Variances in the tolerances of each part built does make a difference in the operation. Chance and quality control give us acceptable couplers.

 Parts in large numbers give you the ability to find the best matching knuckle for each coupler body. When you find "the one", you set the rivet. You would be surprised the difference it can make.

 I found and use, black dental rubber bands for braces, till I get to fixing any issues.