Kato SD40

[mrp]

I have a pair of KATO SD40's that have developed a grinding noise over the years. I think they are both original run, as they have Aztec milled frames.
They have been fine for years, with the grinding noise a recent development.
I tried cleaning & oiling everything but no luck. Also replaced the brushes.
When I run the mechanism without the trucks, the noise persists.
Any thoughts?

Michael Pennie

[peteski]

That is odd Michael.  Are you sure the noise is grinding rather than some sort of vibration?  Did you lubricate all the bearings?

Anyway, if the noises is still present in a truck-less chassis, there aren't that many moving parts left.  Other than the motor, there are only worms with their bearings and the drive shafts (IIRC).  remove the driveshafts to decouple the worms from the motor (or take the worms/bearings out too). If the noise is gone then you know that you need to look at the parts which were removed. If the noise persists then it is the motor.

Does the armature rotate freely?  Maybe there is some debris stuck to the magnets, rubbing against the armature?

[u18b]

N Scale Mag has had an article in their files by me for years on this subject (wish they would publish it).

It is a problem solving flow chart that helps you find problems in locos based on the noise you hear.

Maybe one day they will get to it.  I think it would help a lot of people.


Follow Pete's advice and report back here.
Remove the shell and trucks.

Turn loco upside down and apply power.

Is the noise still present or gone.

If still present, then problem is in the mechanism.

If noise is gone, then problem is in the trucks.

Also, the KIND of noise is important.

The kinds I identify are: 

Scraping
screaching
rumbling
and clicking

"Grinding" appears to be closer to "rumbling."

My chart identifies about 14 possible causes.

[mrp]

Gents

Screeching or scraping might be a better choice of words.
Tried it with removing the inner bearing block for the worm gear. This helped some, but still not right.
After fiddling some more with both engines, I added a couple more drops of oil to the motor shaft, between the end  of the motor and the flywheel.
This did the trick, with both running good as new.
Never had to put oil in that spot before.
Thanks for the help.

Michael Pennie

[peteski]

Screeching is a pretty good indication for lack of lubrication on the fastest rotating shafts (motor or worm), so your fix makes perfect sense.  Motor bearings are metal-on-metal (steel on brass), and are most prone to screech when dry.  If that is an old locomotive then it is not uncommon for the oil in the bearings to dry up.

Good fix!

[tehachapifan]

Ah, yes...the classic screech, which is certainly not unique to just Kato models. I think I heard somewhere along the line that the screeching is actually the result really, REALLY fast vibration of the motor shaft, which makes sense since the screeching always seems to kick-in and out at certain speeds. The remedy has already been mentioned, however I've also heard that too much oil applied where the shaft enters the motor can cause oil to get into the motor and potentially lead to other problems. Never experienced this, but I was always careful anyways. I've also sometimes found the need to apply a tiny bit of oil where the shaft enters the worm bearings as well to get the screech to completely go away.

[u18b]

Gents

Tried it with removing the inner bearing block for the worm gear. This helped some, but still not right.....

Michael Pennie

Michael,
I assume by referring to the inner bearing blocks that you are talking about my procedure.  What many people have called "Beardenizing" a loco.

But please understand.  That procedure ONLY works on locos without a u-joint.
Most (though not all) 4 axle units have no U joint--- and that procedure works well.

But an SD40 DOES have a u-joint-- and so you should not do it.

The purpose of removing the inner bearing blocks is to remove any possible mis-alignment of the motor shaft with the worm shaft.
But.... a U-joint does that automatically!

Further, when a u-joint is present, the worm can now actually flop around if the inner bearing block is removed.

Any way,  hope that help.