Marx 333 Steam Engine has a Problem

Yes, you want to check resistance between any two commutator segments followed by the next two segments and finally the third possible two-segment combination. You can do it with the motor assembled by checking resistance between the two brushes with the armature in each of the three possible combinations of two commutator segments contacting two brushes. If the three readings are very close to the same the armature is good. Others here will probably post the correct resistance number. 

take a good look at the field coil and armature windings they should look a dark redish color if the coils are dark brown or black the windings have been over heated and are shorted. would need to be rewound or buy another motor. also you w ant to check from each winding to the metal armature shaft  or frame on  field and armature windings   Alan

Yep, 3 tests between the plates; equal readings, 3 tests from plates to shaft, field coil wire to plates/chassis.

A short in the field can be tough as it can simply move the magnetic "sweet spot" ; essentially screwing up the pull's timing.  It's just an electromagnet. You could try to swap the field leads to see if the sweet spot moves to a more favorable position in relationship to the arm..

If an armature commutator plate spins on the shaft even a couple degrees, that would also throw off the magnetic timing.

Dust the gaps between plates well. Brushdust causes my Marx to go from using 9-10v bashee to 18v slug. A quick dust always wakes it up again. New brushes often make a lot of dust until thing break in again

Thanks for the replies.  I took off the brush holder on both of my Mark 333 engine motors.  The one that runs fine showed an ohm reading of 2.5 ohms between each armature contact section.  A 0 ohm reading was shown between each armature section on faulty engines motor.  So the armature of that engine motor is open and faulty.  It is amazing that it will run at all even with pushing and 18 volts.

That engine will be "bad carded" until I can find a replacement Marx 333 armature.  I checked a Marx 999 spare I have and its armature is too small.

Charlie

Correct the spelling in your thread title go read Marx, not Mark. (You probably keep getting incorrectly autocorrected by your browser spell check.) Correcting the title will help others who later search for information on the Marx 333.