Legacy SD90MAC speed issues during lashup

The 6-82757 SC90MAC is an RCMC equipped modern Legacy engine, and it's clearly having a problem, it shouldn't run like that.

Just a thought, have you checked the momentum setting on that engine?  Is it the set the same as the other engines in the lashup?  I have had issues in the past with engines in a lashup not running at the same speed and it ended up being that the momentum setting was different for the engines in the lashup.

I don't think it's the momentum setting based on the jerky running, looks like something's actually amiss.

My top suspect is the drive nub on the bottom of the motor.  The twist-off trucks are famous for this breaking free of the motor shaft and losing motor drive.

It's easy to twist the truck off and check these, no need to remove the motor from the frame.

If they're loose, I clean up the shaft and drive nub and bond it with Loctite 660 Retaining Compound.  To do this repair, you don't even have to take the shell off.  Just be sure not to lose the coupling between the motor nub and truck, it's loose and is easily lost.

If the drive nubs are locked on tight then inspect traction tires and side frames.  I had an SD get a traction tire get caught up on the side frame brake and really bogged it down.  

@gunrunnerjohn posted:

I don't think it's the momentum setting based on the jerky running, looks like something's actually amiss.

My top suspect is the drive nub on the bottom of the motor.  The twist-off trucks are famous for this breaking free of the motor shaft and losing motor drive.

It's easy to twist the truck off and check these, no need to remove the motor from the frame.

If they're loose, I clean up the shaft and drive nub and bond it with Loctite 660 Retaining Compound.  To do this repair, you don't even have to take the shell off.  Just be sure not to lose the coupling between the motor nub and truck, it's loose and is easily lost.

Do you think it’s safe to run the CP in a lashup as is or is it to risky

@Diego posted:

Do you think it’s safe to run the CP in a lashup as is or is it to risky

I'd try to fix it before trying to do that, something is certainly wrong with it!

@gunrunnerjohn posted:

I'd try to fix it before trying to do that, something is certainly wrong with it!

I recently received another SD90 but this one is TMCC #9107 this one barely moves. I was wondering if you believe it’s broken. This one i unboxed today and I can’t even operate it at all.

@gunrunnerjohn posted:

I'd try to fix it before trying to do that, something is certainly wrong with it!

I took the wheel off of 9116 didn’t see anything to alarming.

@gunrunnerjohn posted:

I'd try to fix it before trying to do that, something is certainly wrong with it!

I took the wheel off of 9116 didn’t see anything to alarming.

@Diego posted:

I took the wheel off of 9116 didn’t see anything to alarming.

Did you make sure the nubs on both motors are secure and not slipping on the shaft?  Take that coupling off the motor and check the motor shaft nubs.