One motor runs faster than the other.

This is pretty common for the non-tach motor to run slower and to see some studdering at slow speeds (less than 5 smph) with no load.

Does it stop studdering at any speed or under a load by a consist?

In your test above, if you artificially apply load to the tach motor with your fingers, does the other motor match speed?

are you pulling cars when you try this , motor need load and you run at a higher voltage with dcs it should setting down and run together as H1000 has said! Alan

I have encountered this if one motor is binding due to a mounting hole that was drilled at a slight angle. Turn the flywheels by hand to see if you can feel the difference. Rule out debris in the trucks by removing them and rolling them on the tracks. When reinstalling them don’t tighten the screw that holds the motor on the truck tight and see if that helps. If so you might have to add a shim to keep the worm from binding on the worm gear.

Pete

Did this work fine before, then over time it had this condition?  Checking all the mechanical issues, but you can also clean the motor commutator with spray.  Do both.  If one motor has built up dirty commutator from brush dust and dirt it would have a higher resistance.  Run slower.  Armature winding color bright or going dark? G

Is it in series?

I've found that a drop of Deoxit D5 on the commutator of can motors does wonders for their performance, they start at lower voltages and draw less current.

Given the performance free-wheeling, I doubt it's the motor itself. If the tach and non-tach motors ran the same speed freewheeling, then I'd be surprised!

I think I sing with the chorus and figure it's something about having the power trucks actually on the rails that is causing the friction.  Sometimes for MTH stuff it's as simple as a loose motor mount screw.

Thanks for the replies so far fellas.  I'll try your suggestions from easiest and cheapest to hardest.

This engine while "old" was a shelf queen.  My son just purchased it second hand and it had 4 minutes on the chrono and .1 on the odo.   It's quite perfectly new.

@H1000 If I put my finger on the wheel driven by the motor with tac, you can visibly see the other motor/wheel combo speed up.

vr
Ron

Being new, a good break in period also helps smooth things out. Many of my new engines with this behavior are much better after they have a few hundred miles on them.

After all the cleaning, friction,  and mounting issues are eliminated, knowing if the motors are connected together and driven from the same circuit on the board, or does each motor have its own circuit to drive it would be a trouble shooting step.  Reading the actual voltage on each motor while running, and if the same, then cutting one motor lead and putting an ammeter, one of your VOM or DVM ranges,  in line and reading the current drawn by each would be another to see if they are equally carrying their load.

For MTH engine they are all driven from the same power source.  Even Lionel unless something changed with the newest boards.  Motors in parallel.  G

All Lionel motors on TMCC/Legacy command engines are in parallel, at least I've never seen them in series in the many hundreds I've had apart.

Just an update.

Started with motor and gear inspection found nothing.

Ran engine for a while at 45 SMPH in an attempt to break in.  Ran for about an hour and a half.  Not much improvement at slower speeds.

Noticed the traction tires looked old and maybe the start of dry rot.  Minor improvement.

Old

New

Sprayed some of that deoxit D5 on both motor commutators.  Pretty big improvement.

Can go nearly any SMPH now smoothly.  I do have three sections of poor track work where the engine will stall at 10 SMPH.  The two drive wheels are just too close to one another.  The front drive wheels actually loose contact with the rail and the rear motor is not powered high enough to push it through at speeds lower than 10 SMPH.

Sounds like you're done, time to do some trackwork.