MTH 20-80007A PRR L1s Issue

I would start by checking for binding in the driveline. Look for bent rods, or rods that were assembled incorrectly.

I had the shell off and rotated the flywheel by hand.  I could not detect any binding, and the drivers appear to be correctly quartered

Definitely might need to remove the shell. Yes, you have it right that on MTH engines, the tachometer flywheel is used both for speed control, but also the chuff rate function. So if chuff is steady and constant, then the motor and flywheel are  spinning consistently. I don't have an example of this engine and did not see a parts breakdown. What I'm getting at, it points to what you eluded to, somewhere past the flywheel between the motor and wheels.

One of those remove the shell, hold the wheels, and try to spin the driveshaft by hand to see what might be slipping.

Edit- again, what you would carefully need to figure out is holding the main drive wheels, and then applying torque to the flwyheel or drive shaft- maybe draw a stripe on the shaft or couplings to see what if anything slips.

If the drivetrain is not binding anywhere, then I would focus on making sure everything is properly lubricated and then checking for either a dirty, damages, or loose tach strip and also making sure the tach sensor is not partially obstructed or dirty and that it's spaced properly.

If none of that resolves it, I'd probably start to suspect the board itself.

PS2 and PS3 locomotives have never been great runners from about 1 to 3 Scale MPH but after that usually even out and run perfectly. I guess it's possible that with the particular driver size and gear ratio of that loco, it might be erratic up to 6 SMPH. That would be unfortunate, and very surprising.

That may use the double gear box so it is possible a gear slipping on axle.  Pat may have experience with that specific model to know if it had an issue.  I have not run across it.  But, hearing chuff is subjective.   Is the track clean, no other engines experience this on your layout.  Clean wheel and pickups.  A voltage drop of track power to the PS-2 board and PV to motor can cause speed fluctuations on a layout.  G

Lubricate pickup rollers sparingly. Might help.

All, thanks for the replies.  I have two other MTH engines, one PS2 and one PS3 running on the same track. None of the other engines have this problem.  All my other MTH engines have buttery smooth slow speed operation. I should add that when the L1 has this problem I can count the chuffs when the the model slows.  The chuffs increase to more than 4 per revolution (which is what I have set).  Again, the model is behaving as if the motor RPMs and the corresponding chuff rate is being regulated properly for the smph set, but the drivers are not keeping up.   I’ll try to get a video of the issue this weekend.  

Are the wheels slipping?  Random anywhere on track or just certain curve or section?  Loading effect it less or more cars?  G

Odd behaviors like this are usually mechanical issues. Could be failing dog bone, loose flywheel, or slipping cup, bad motor, bad worm shaft main bearing(s) etc, etc, …definitely has to be opened up for an examination of all mechanicals. If problem isn’t readily apparent, temporarily disconnect motor leads, and solder in wires to direct drive with DC source on rollers. Apply load by putting slight pressure, and examine drive line motion. This would tell the story, or at least rule out mechanical involvement.

Pat

@GGG posted:

Are the wheels slipping?  Random anywhere on track or just certain curve or section?  Loading effect it less or more cars?  G

Hi George, wheels are not slipping and the problem appears to be random anywhere on the track.  I have not explored a load effect as my current "layout" is no more than an 8ft shelf.  My engines simply travel back and forth without any cars.  Included below is the coal tower scene with the subject L1 on the left.   Since my set up is so small slow speeds are the rule (I set a max speed of 12 smph) for all my engines.  Typical running speed for me is 3 - 5 smph.  This environment makes the slow-speed quirks of this loco really apparent.

@harmonyards posted:

Odd behaviors like this are usually mechanical issues. Could be failing dog bone, loose flywheel, or slipping cup, bad motor, bad worm shaft main bearing(s) etc, etc, …definitely has to be opened up for an examination of all mechanicals. If problem isn’t readily apparent, temporarily disconnect motor leads, and solder in wires to direct drive with DC source on rollers. Apply load by putting slight pressure, and examine drive line motion. This would tell the story, or at least rule out mechanical involvement.

Pat

Hi Pat,

While I can be fairly competent with some fixes, I am definitely not a an MTH ASC!  The diagnosis and the fix for this may quickly exceed my abilities!

I'll try to post a video later today to illustrate the problem.  Hopefully that will more fully inform next steps.  I am happy to send the model off to someone more capable than me for further diagnosis and repair if that is the best path.

Scott   

@Scott R posted:

Hi Pat,

While I can be fairly competent with some fixes, I am definitely not a an MTH ASC!  The diagnosis and the fix for this may quickly exceed my abilities!

I'll try to post a video later today to illustrate the problem.  Hopefully that will more fully inform next steps.  I am happy to send the model off to someone more capable than me for further diagnosis and repair if that is the best path.

Scott   

6 of one, half dozen of the other,…you can send it to me or George, doesn’t really matter, I can throw a rock & hit George’s place, and he I, …..if it’s a mechanical issue, I’ll fix it, if it turns out to be an electrical issue, I’d pass it on to George, or vise versa…..

Pat

thanks Pat.  I didn’t have time to post a video yesterday. That will have to wait till this Friday.  I’ll do that, then we’ll go from there

Scott

You might want to break it in on a temporary oval first.  Interesting seeing a significant speed change when only moving 3-5.  G

Life happens, I've been busy lately and it's been more than a month before I was able to get back to this engine.  I ran it again today, but thoroughly cleaned the rails first to eliminate that as a problem for the erratic behavior.  No doubt it performed better.  It initially stuttered at lurched forward on the first attempt, but then settled down after several runs.  It still noticeably slowed slightly a couple of times.  Maybe it just needs a good break-in period?  I did grease and lube the engine when it first arrived.  I'll keep running it and see if the problem comes back before I ship it off.

FYI, my two other MTH steamers run on the same rails with not problems at all. 

Your problem sounds electronic rather than mechanical to me.  My top suspect would be some kind of failure related to the speed control circuitry.

With MTH PS2/PS3, is there a way to turn speed control "off"?  If so, you could try doing that.  Run the loco for 15-30 minutes and see whether it still exhibits stuttering, lurching, or noticeable slowing.  (Without speed control, SLIGHT slowing might be expected on tight curves.  Otherwise it should run fairly smoothly at slow to moderate speeds.)

Please try this and let us know what you find.  Good luck!