[COLOR="Blue"]Do I need a new motor again?[/COLOR]
Always a possibility but it is rare that a new motor will not run.
Check the windings for continuity.

You said; you had 250 but did you check that you had both sides of the line when referenced to Neutral re: 120 volts. The motor needs 120. Perhaps you have lost Neutral.

When checking fuses etc., did you disconnect one side of the device you were measuring? This ensures that you do not read an alternate/parallel circuit path.

The power cable was a little split and corroded, so I replaced it. The dryer ran for a couple of hours and now it is dead again. I have a good 123 V at each pole on the power block. All the internal wiring looks good - no obvious shorts. What else can I check?

Thanks for responding. I have traced all the wiring to the motor. I have 120V at the red wire coming from the power block to pin 2 on the motor and 120V at the blue wire to pin 4 on the motor. The black wire (pin 6) to the white wire (pin 5) reads 0 ohms when the start switch is pressed. The ground wire (green/yellow) checks out ok -0 ohms to neutral. The red wire at pin 1 seems to feed back into the dryer working its way through all the fuses which I rechecked. They all read 0 ohms when disconnected except the cycling thermostat. That reads 0 between the red wire connections, but about 7,000 ohms between the purple wire connections. The purple wires seem to connect the temperature select switch to the timer motor assembly. I don't know if this is right, but I'm buying a new cycling thermo because it's so cheap as well as new rollers for the drum as it seems kind of hard to turn. How do I check the motor to see if it is ok. It is brand new, and the second new one I tried in less than a week, but you never know. Oh yeah, the heating element checked out okay - no short circuit.

I am doing a bit of guessing here but am fairly confident that I have it correct.
I am assuming that you used Neutral as the reference for all your readings.

[COLOR="Blue"]I have 120V at the red wire coming from the power block to pin 2 on the motor[/COLOR]
This looks normal as it is L2 voltage. It is one side of the centrifugal switch for the heater.
[COLOR="Blue"]
120V at the blue wire to pin 4 on the motor.[/COLOR]
This also looks normal It is L1 voltage to the common connection on the motor.

[COLOR="Blue"]The black wire (pin 6) to the white wire (pin 5) reads 0 ohms when the start switch is pressed.[/COLOR]
This also looks good. Those 2 points are directly across the start switch.

[COLOR="Blue"]The red wire at pin 1 seems to feed back into the dryer working its way through all the fuses[/COLOR]
Yes, this is the other side of the centrifugal switch for the heater

Check from 4 to 5 for continuity. You should see about 2 ohms, this is the 2 motor windings wired in parallel.

Also if you measure to 5 or 6 you should see 120 volts when powered up. This is the L1 voltage (same as pin 4).
When you push the start button it should drop to zero. If it does not my guess would be that the door switch is toast.

The wiring diagram I linked is pretty poor quality so here is what the different connections should be.
1 - RED - heater centrifugal switch - to heater
2 - RED - heater centrifugal switch - to L2
4 - BLUE - left hand side of motor - common for both windings.
5 - ? - right hand side upper of motor - main motor winding and motor centrifugal switch
6 - BLACK - right hand side lower of motor - parallels the start switch - when the motor gets close to operating speed it disconnects the motor's start winding and connects across (parallels) the start switch so you can release the start switch and the motor keeps running.

I hope the above is more helpful than confusing.

[COLOR="Blue"]From everything I've read the centrifugal switch in the motor should keep the motor running after the start switch is released.[/COLOR]
That is correct.

[COLOR="Blue"]Now the dryer will run for anywhere from 1 to 20 minutes before quitting, or it won't run at all unless the start switch is pressed in. I tried all three motors, same results. Could it be the drag from the drum is causing the motors to quit?[/COLOR]
I cannot see 3 motors having the same problem so it must be something external to the motor. Try rotating the drum by hand. It should turn fairly easily.
You may want to try this on a couple other dryers to get a feel for it.

[COLOR="Blue"]Could it be the start switch?[/COLOR]
This is a possibility. One scenario would be that the contacts in the switch are pitted and dropping the voltage to the motor and this low voltage is causing overheating.
The problem with this is that once the unit starts up, it switches over to the centrifugal switch and therefore they are not in circuit once the unit is running.

I am pretty well stumped on this one.

I am going to post this in the tech section.
I may have missed something that someone else will see.
Perhaps someone else has the wiring diagram for this unit and will be able to find where I went wrong.