Tsunami2 surging

[spookshow]

I recently purchased an N scale Kato ALC-42 Charger with a factory-installed Tsunami2 decoder. It seemed to be fine when I first got it, but now it has developed this annoying habit of surging up and down (go fast, go slow, go fast, go slow). This is particularly pronounced at full throttle. It's also very herky jerky when it first starts moving.

Example - Throttle up to speed step 28. Locomotive starts moving and is herky jerky for a few seconds. After about 30-40 seconds it reaches top speed and then about 10 seconds later it starts surging up and down.

I thought maybe it was BEMF related and tried setting CV212 to 0, but that didn't seem to have any effect.

Any suggestions?

Thanks,
-Mark

[spookshow]

You know what, nevermind. I think this is going to turn out to be some sort of lube issue.

-Mark

[peteski]

I would be very surprised that any Kato model would have lubrication problem.  Especially brand new one. They run smoothly, dry or oiled.

Any chance you could try running it on DC (even with the decoder still installed) just to check the behavior?

[spookshow]

As the surging gradually worsened, I noticed a distinctive screeching sound had started occurring during the slowdowns - a sound very much reminiscent of dry bearing blocks. So, I pulled the trucks out and lubed all the gears and, most importantly, the two ends of the wormshaft. And yes, that solved it.

So go ahead and be surprised 

One reason this may have been an issue with this particular locomotive is that it is one of the just released DCC-Sound versions, which means it's probably been sitting for a year+ waiting for a decoder install. IE, it's not brand new, even though it was just released.

-Mark

[peteski]

I am surprised.
I am quite familiar with the screeching sound of the motor and/or worm shafts, but even if a loco was sitting for over a year, the lubricant shouldn't
t have dried up that fast. What surprises me even more is that this would cause waves of increased friction high enough to slow the motor down. I have never seen this happen and I have dealt with many dry shafts.    The culprit is usually the motor bearings (since with sintered bronze bearing an stainless steel shaft metal-to-metal friction causes screeching). With most Katos, the worm shaft rides in slippery plastic bearings which are usually not lubricated at all.

Anyway, good to know what the cause was and how you fixed it.  One's never too old to learn about a new problem and its resolution.

[spookshow]

I definitely haven't solved all of this thing's problems. Although it doesn't surge/screech at the high end of the throttle anymore, it's still insanely herky jerky at the low end of the throttle. I tried resetting the decoder, but that didn't help any. I may just return it.

-Mark

[peteski]

Interesting.

[spookshow]

Running this thing on its back where I can watch the gears, wheels and driveshafts spinning, the rear driveshaft is definitely spinning much slower than the forward drive shaft. It doesn't spin at all at speed step 2 and doesn't really get going until speed step 4. So, at slow speeds you have one truck spinning like it's supposed to and one truck that's not spinning or barely spinning, which leads to wheels slipping and herky jerkiness. Once you get above step 7 the rear truck is going fast enough that the wheels are not slipping anymore, so it runs more or less normal. And I guess the plausible explanation here is that the rear flywheel is slipping on its motorshaft. But whatever the case, it's going back to Kato.

-Mark

[nscaler711]

Oh sweet a Charger and a Kato at that getting a less than ideal grade. Never thought Id see the day.   


I was going to ask if you had another Charger on hand to swap the motor, driveline and trucks out and see if that solved your issue. I can honestly say I have yet to see a Kato run horribly out of the box, like new anyway. 

[peteski]

So the plot thickens . . .

The type of problem Mar describes id not flywheel (those are solidly press-fit onto the motor shaft. They ain't movin'!
Most common cause is split universal (plastic) coupling on a metal shaft (like worm shaft).
In this model the universal coupling on the flywheel side  is a hex-shaped piece molded with the plastic shaft riding in a hex-shaped opening in the flywheel. Not possibilities that it could be damaged in a way which would cause slight slippage.

The other end of the drive shaft rides in a universal coupling cup press-fit in the metal  worm shaft. That could possibly split and slip on the worm shaft, but I  have not seen this problem on with these particular coupling cups.
However the Charger uses trucks with those fine-toothed gears and the worm is  integral on the truck. These are rather delicate and a possibility is that the worm retaining cover has popped partially off causing the worm not to engage the worm gear, csausig slippage. Fix might be as easy as snapping the cover back on.

This problem should be easy to identify.  If the wheels can be spun if you try to turn the defective truck's wheels with your fingers, then the work cover has unsnapped.  If the wheels cannot be turned, then the problem is elsewhere (like a split universal coupling cup).

However, taking this model apart is quite difficult and returning it for repair/replacement seems like a good option.  This is one of those Kato models I think they over-engineered and made it too complicated to service. Very well made, but a pain in the butt.

These locos have another possible defect.  Some of the gear cases have area of their side walls too far apart causing one of the idler gear axles to jump out of the bearing hole, but that would likely show a different type of a symptom.

[spookshow]

If the motorshaft is spinning but the driveshaft isn't, how could that be anything but a loose flywheel?

-Mark

[peteski]

If the motorshaft is spinning but the driveshaft isn't, how could that be anything but a loose flywheel?

-Mark

These brass flywheels are tightly friction fit onto the motor shaft. Unless the hole in the flywheel is larger enough for the flywheel to fit loosely onto the motor shaft? But if that was the case, I image that the flywheel would have fallen off when the model was assembled at the factory. 
Unfortunately because the motor is mounted off-center, only the front flywheel is visible when looking at the bottom of the model.

Would you be willing to try something for me if you have pair of pointy tweezers?



Looking down the chassis in front of the rear frame you can see the plastic driveshaft.  When the loco is running on its back fast enough for the rear truck's wheels to spin (slower than the front truck's wheels), insert the tweezers down the drive shaft tunnel and pinch the driveshaft.  Can the pinch stop the driveshaft (and rear truck's wheels) from spinning while the motor and front truck are still running?  I want to do this instead of just stopping the rear truck's wheels with a finger (which I guess you could try too).



Or maybe since you have taken the rear truck out for your online review, could you take it out again and while running on its back, stick a screwdriver or similar tool down the driveshaft tunnel, and see if you can stop the rear flywheel from spinning. My brain just can't accept the flywheel being that loose on the motor shaft.

[spookshow]

I don't have it anymore, it's on its way to Illinois. But I know for a fact that that rear driveshaft was not moving at speed step 1 and 2, while at the same time the forward wheels were turning.

-Mark

[peteski]

I don't have it anymore, it's on its way to Illinois. But I know for a fact that that rear driveshaft was not moving at speed step 1 and 2, while at the same time the forward wheels were turning.

-Mark

Oh well . . .
That is the weirdest thing!

[Nick Lorusso]

Mark,
It should have been an ESU decoder. but I see you found a worm gear option.