Lionel locomotive only runs in reverse

The problem is in the 'E' unit. Either the unit is wired incorrectly, or the contact 'fingers' are not making proper contact with the drum. Inspect the contacts to insure they are bent properly and do not have any holes burned through them by arcing.  Make sure the drum is in good condition, and polish the copper strips on it.

Larry

I agree with Larry.  Here is the wiring diagram to help:

Thank you both, I will keep at the e-unit.  One thing I'm still unclear on is the positioning of the fingers on the four-finger piece.  Does anyone know if they are supposed to all sit on "top" of the drum, or if two are on "top" and two on "bottom"?  When initially disassembled, they appeared to be split two and two and that is how I have them now, but thinking they are supposed to be all on one side?

The piece with four fingers should have all fingers in line with each other touching the same side of the drum. I'm not even sure how they can be bent to be on opposite sides.

The other two finger unit has both fingers contacting the opposite side.

Swap the brush connections first to narrow it down to the E-Unit before tearing into it.

Rob, it has a grounded brush.  May be swap the field connections.

@David Johnston posted:

Rob, it has a grounded brush.  May be swap the field connections.

Either the brushes or the field leads, it doesn't matter. Both will reverse the direction.

Thanks everyone, I pulled the e-unit and verified the motor works fine in both directions.  I suspect the e-unit fingers are just too warped/bent and two of them possibly broken off short.  Debating a full new e-unit vs. just replacing the fingers and drum.  The plunger mechanism seems to work fine so I think doing the fingers and drum might be sufficient... or since I've gone this far with it already, is it better to be safer and replace the whole thing?

No, just replace the two finger boards if the drum looks good.

I see a major electrical problem. The lockwasher on the LH side of the brushplate needs to be on the right. It needs to be there for the ground circuit.

Just wanted to say a belated thank you to everyone for their input.  After replacing the finger boards and drum, I have a fully functioning engine!

Late to this thread and glad you have it figured out with the fine folks advice here.

The 204 engine has been a  great runner on our small 4x8 layout for years.