Best Of *Science* of solving N scale diesel mechanism drivetrain vibration noise?

[u18b]

John,
I found a GREAT benefit to drilling a hole in the area over the worm gear so that I could SEE the gear mesh.

You can see that I was able to adjust the worm on my brass EP-2 so that just a little daylight is between the tips of the teeth and the bottom of the worm.

The same thing could help you since you are making mods that effect this interface.

[Jim Starbuck]

Great input here.
Going back to the original question about  instruments or tools that would help diagnose noisy locomotives a few come to mind. A few are just common sense and are likely already on most modeler's benches.

A flat surface such as a machined steel block, glass or even a piece of planed hardwood to use as a benchmark to make sure frames are straight and not bent or twisted.

A digital caliper or micrometer to measure various thicknesses and depths.

A multimeter or instruments to read voltages and milliamp draw. This has been covered well in previous posts.

A dial indicator and base to measure shafts worms and flywheels to make sure they are running true on axis.

A good magnifier such as an optivisor. We are working on some pretty small mechanisms and searching for often times minute flaws in them.

Good lighting. Not much explanation necessary here.

Quality jeweler's screwdrivers. Sounds odd but it does help and gives finer control during disassembling and reassembling.

Just some rambling thoughts and typing out loud.

[jagged ben]

....

* What is the Atlas part number (or Intermountain part number) to order for replacement?
* Is it worth it to just get the replacement case and easy enough to transport the gears into the new gear case?
* Or is that difficult enough, that one should just order replacement trucks?
   
...

9490301
http://shop.atlasrr.com/p-3654-n-sd-60-gear-case.aspx

And yes, at that price it's worth it, in my opinion.  You can get a complete truck too, but note they only sell them with black sideframes.

This truck is not a difficult disassembly/assembly, as long as you know the tip to get the brass contacts back on the correct sides.  (Ron can fill you in.)   

[jagged ben]

Continuing on the subject of the easily breakable pin, let's compare to a Kato Dash-9 truck.

[ Guests cannot view attachments ]

As I've noted in the pic, the Kato truck has the same type of support pin, but there are reinforcing plates to prevent breakage. 

Another note:  look at how much bigger the Kato idler gears are.   I have barely ever studied gear ratios, but I believe that, along with gear play tolerances, this also has something to do with how free rolling they are.  The intertia of the spinning axles doesn't have to work as hard to move the idler gears.   

[u18b]

Ben is exactly correct.  I had forgotten.  Wow.

The pickups are NOT symmetrical on HTC trucks.  There is a right side and a left side pickup.  If you put two lefts on one truck, performance will degrade.  On the old Atlas thread, I figured out what Atlas/China was doing back then.    In fact, it may not run as well if you put a left on the right side and right on the left side.

I have no idea what they are doing now.
The last HTC loco I bought was the original run SD45-2 IM.  And that has been a while ago.

[jagged ben]

Ben is exactly correct.  I had forgotten.  Wow.

The pickups are NOT symmetrical on HTC trucks.  There is a right side and a left side pickup.  If you put two lefts on one truck, performance will degrade.  On the old Atlas thread, I figured out what Atlas/China was doing back then.    In fact, it may not run as well if you put a left on the right side and right on the left side.

I have no idea what they are doing now.
The last HTC loco I bought was the original run SD45-2 IM.  And that has been a while ago.

Yes, if you don't match the left and right to the correct sides the axles are skewed and things go badly.  There's a little tab on on or the other to get it right.  I forget which but if you just watch the alignment of parts carefully it's not hard to make sure you're doing it right. 

I'm pretty sure no parts have been changed in 20+ years.  And that's the annoyance here, for me.   Maybe we can lobby Atlas to update their tooling after all this time.  Or even get an aftermarket truck replacement made for these, i.e. a replacement gear case and gears.  I'd be down to buy ... let me count my engines ... 26 or more replacements.   Probably more because I plan to buy a couple new IM units with sound. 

[u18b]

I guess an R or an L would be good if you are going to peen anyway.   

[tehachapifan]

Thankfully, I have not had this happen to any of my SD50/60/40T or 45T's yet (as far as I know) but now I know what to look for first should one of them start to act up.

[rrjim1]

The fly in the ointment is that in order to balance the armature, it has to be removed from the motor.  Which means that both flywheels have to be removed, and then the motor completely disassembled.  Afterwards the flywheels have to be pressed back on.  Without special tools in a home workshop you can slightly bend the motor shaft during this process. At that point all the balancing you just did is wasted.

Well he has over a dozen bad $25+ motors, all it take is a good puller to remove the flywheels. I have done 30+ and have never bent a shaft. A balancer can be made out of two straight edge razor blades. Pressing the flywheels back on is were one can bend the shaft, as long as one uses a little common sense instead of a hammer it can be done fairly easy.     

[atsf_arizona]

I've often toyed with the idea that the next one I get that's broken I'll try to make a pin with some of the wire we use for the throws for the Tortoise machines on our club layout.  Might be a little more robust and take all the handling that these go through at times.

also quoted:    Maybe drill a little hole and put in a metal post with superglue?

I did think of this same idea too on "how to repair a broken-off mounting tab" on these IM and Atlas trucks.

Then it occurred to me that using one *metal* post or *metal pin* running through the truck case as replacement mounting tabs won't work.

Because the two halves of the *split frame metal mechanism* rest directly on the tabs, and these two halves must be electrically isolated from each other.   

If you did install single long metal post or metal pin as a replacement "mounting tab" and then laid the split frame mechanism on top if it..... the metal post/pin would create a  *dead short* between the split frame halves,  the minute that you put the mechanism on a powered up DC track.   

Or worse, you could accidentally melt a plastic sideframe or even fry a $30+ DCC decoder (or worse, a $70+ sound decoder) if you tried putting such an mechanism on a live DCC-powered track, if you hadn't realized this dead short would happen.  (So, don't do that    )

From reading the above, it seems easiest way to repair the truck, is to get the replacement case, or buy replacement trucks.   Regarding the cost, see Jagged Ben's reply #92 above, or my reply #103 below.

[atsf_arizona]

John,
I found a GREAT benefit to drilling a hole in the area over the worm gear so that I could SEE the gear mesh.

You can see that I was able to adjust the worm on my brass EP-2 so that just a little daylight is between the tips of the teeth and the bottom of the worm.

The same thing could help you since you are making mods that effect this interface.

Great idea, Ron.  I may need to do that in my Atlas B40-8 / C628 mechanism.

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Question:

Ron, if you were to guess, what in general should be the proper clearance (in thousand's of an inch) between the "top of the gear tooth" and the "bottom of the valley of the worm gear"?

*  .005"? 
*  .010"?
   
Or would that vary, depending in the model, the gear tooth size, the worm gear angle, etc?

[atsf_arizona]

Ben is exactly correct.  I had forgotten.  Wow.

The pickups are NOT symmetrical on HTC trucks.  There is a right side and a left side pickup.  If you put two lefts on one truck, performance will degrade.  On the old Atlas thread, I figured out what Atlas/China was doing back then.    In fact, it may not run as well if you put a left on the right side and right on the left side.

I have no idea what they are doing now.
The last HTC loco I bought was the original run SD45-2 IM.  And that has been a while ago.

Yes, this good-running SP SD40-T2 you saw in my first original post on this thread, had exactly this problem of the left / right pickups installed in reverse (I assume from the factory), and thus ran quite poorly. 

What you see now:

 

/>
Is the result of my debugging and realizing that *both* IM SD40-T2 trucks where badly binding.  Upon further investigation, the Left Pickup was installed on the right side, and the Right Pickup installed on the left side.  Resulting bind made the loco run jerky and too slowly.   

Yet, it would hobble along "well enough" that one could just assume it was a slow motor / poor mechanism and never investigate further.  Good thing that I couldn't leave well enough alone....... 

After re-assembling the trucks with the pickups in the proper orientation, the loco and mechanism runs extremely well as shown.   

(and yes, the "mounting tabs" are both still present on the trucks on that loco, I checked... that's another reason why it runs so smoothly now).

--------------------------------

As previously stated in this thread, here's Ron Bearden's "gold standard" Atlas Forum thread, showing how to dis-assembling and repairing the Atlas SD50 / SD60 and Intermountain SD45-2 / SD45-T2 / SD40-T2 trucks, which includes excellent pictures and discussion of the asymmetrical left side / right side needle point wheel holders:

http://forum.atlasrr.com/forum/topic.asp?ARCHIVE=true&TOPIC_ID=42265&whichpage=14

(As we have seen, during his 30 years of doing N scale locomotive tuning, Ron Bearden has probably forgotten more about N scale diesel locomotive tuning than most of us may ever learn   )

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I also years ago, found another gold standard Internet article on dis-assembling and repairing the Atlas SD50 / SD60 and Intermountain SD45-2 / SD45-T2 / SD40-T2 trucks, which includes excellent pictures and discussion of the asymmetrical left side / right side needle point wheel holders. 

It's by Colonel Andre Kritzinger of South Africa, and has been a great resource and in existence for over 10 years: 

http://mysite.mweb.co.za/residents/grela/atlaskatotruck.html

Here's Andre's versions of the truck dis-assembly / assembly and left/right pickup pictures, which mirrors Ron Bearden's.

In the final picture, you can clearly see the "mounting tabs" are in place on the truck used by Intermountain SD45-2 / SD45-T2 / SD40-T2 and Atlas SD50/SD60 locos:   









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In this final picture from that web page, you can clearly see the "mounting tabs" are in place on this SD50/SD60 Atlas HTC truck (which is the same truck used by Intermountain on their SD45-2 / SD45-T2 / SD40-T2 locomotives):



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You can see other excellent locomotive tuning tutorials on Andre's site, including decoder installs,  how to dis-assemble the LifeLike SD7/SD9 locos, etc.  Check it out .

[u18b]

Great idea, Ron.  I may need to do that in my Atlas B40-8 / C628 mechanism.

-------

Question:

Ron, if you were to guess, what in general should be the proper clearance (in thousand's of an inch) between the "top of the gear tooth" and the "bottom of the valley of the worm gear"?

*  .005"? 
*  .010"?
   
Or would that vary, depending in the model, the gear tooth size, the worm gear angle, etc?

John, remember, there are TWO measurements since everything is not totally locked down and rigid.
Meaning the truck has up and down play.

First, there is the distance pictured.  This is when the truck is pressed tight up against the chassis.  I don't have a scientific measurement.  I just look for daylight.

But there is a second measurement/consideration. When you PULL the truck downward, do the teeth STILL engage.   As Peteski indicated, the torque of the worm angled making the truck gear move makes the two want to separate. If the worm can lift it will (usually it can't ). So the force can potentially lift the entire half of the loco.  If the truck retaining parts allow the truck and the chassis to move two far, then two teeth will pass each other and the chassis will drop by gravity.  The process repeats for each tooth making a distinctive wratcheting sound similar to a socket wrench.

So in answer to your question I have no precise answer. 
Closest approach- still daylight.
Fartheresr separation- teeth still mesh.

That's about all I go by.

[atsf_arizona]

9490301
http://shop.atlasrr.com/p-3654-n-sd-60-gear-case.aspx

And yes, at that price it's worth it, in my opinion.  You can get a complete truck too, but note they only sell them with black sideframes.

This truck is not a difficult disassembly/assembly, as long as you know the tip to get the brass contacts back on the correct sides.  (Ron can fill you in.)   

===================

Jagged Ben, thx.

All, the tips on how to get the truck's left and right wipers back in the correct way, is listed in the threads referenced above in previous reply #101.

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All, FYI, I looked up the cost for the replacement part number 9490301 for the Atlas gear case, the cost at Atlas parts website is $1.30 each.

http://shop.atlasrr.com/p-3654-n-sd-60-gear-case.aspx

I also looked up the price for the complete truck too from Atlas, part number 9490300, cost per truck is currently $5.45 each:   http://shop.atlasrr.com/p-3653-sd-60-truck-assembly.aspx   

In my checking around, that is a very reasonable price.  Depending on one's dexterity and time availability, a valid alternative to swapping the gears yourself.

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The fact that Atlas only sells the complete trucks with black sideframes, could be handled by brush-painting the sideframes with the acrylic paint color of your choice.   
I've done that and I have had no problems with the paint adhering to the truck sideframe's plastic.

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FYI:

The schematics for that Atlas SD50 and SD60 mechanisms are here, which show the full part numbers list for these trucks, the left/right pickups,  the entire Atlas SD50/SD60 mechanisms.
The truck part numbers are the same for both the Atlas SD50 and SD60:

http://www.atlasrr.com/pdf/N%20SD-50%20DIESEL%20LOCO%20CHINA.pdf
http://www.atlasrr.com/pdf/N%20SD-60%20DIESEL%20LOCO%20CHINA.pdf

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In case you're not already aware, the Intermountain SD45-2 / SD45-T2 / SD40-T2 all use the Atlas SD50/SD60 trucks, the Atlas SD50/SD60 motor, and I suspect some of the other SD50/SD60 mechanism parts as well (I don't have a full inventory).    A discussion of those similarities / differences is in this www.theRailwire.net thread:   https://www.therailwire.net/forum/index.php?topic=27764.0

At the same time, in case you are thinking of other parts swapping.... be aware that Intermountain clearly has it's own mainframe / split frame mechanism sides.  Also, the wheelbase for the SD45-T2 / SD40-T2 is longer than the SD45-2.  Thus  if you have a broken or cracked universal joint (these can crack causing the loco to stop moving even though the motor spins) in the SD45-T2 / SD40-T2...... that you get the correct length universal shaft.  If I remember correctly I think (but haven't verified lately) that the IM SD45-T2/SD40-T2, has a longer universal shaft on one end compared to the IM SD45-2. 

[atsf_arizona]

John, remember, there are TWO measurements since everything is not totally locked down and rigid.
Meaning the truck has up and down play.

First, there is the distance pictured.  This is when the truck is pressed tight up against the chassis.  I don't have a scientific measurement.  I just look for daylight.

But there is a second measurement/consideration. When you PULL the truck downward, do the teeth STILL engage.   As Peteski indicated, the torque of the worm angled making the truck gear move makes the two want to separate. If the worm can lift it will (usually it can't ). So the force can potentially lift the entire half of the loco.  If the truck retaining parts allow the truck and the chassis to move two far, then two teeth will pass each other and the chassis will drop by gravity.  The process repeats for each tooth making a distinctive wratcheting sound similar to a socket wrench.

So in answer to your question I have no precise answer. 
Closest approach- still daylight.
Farthest separation- teeth still mesh.

That's about all I go by.

Great clarification.   

Obvious after you point it out, but I would probably have not realized necessity of the 2nd "farthest separation" measurement ..... until I ran into that problem myself.         

Thank you.

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All, keep the comments coming.   I'm sure this all raises other "scientific" valid N scale locomotive tuning questions, that we can point to answers and continue to crowd-source, here.

Open questions still be pending from earlier in this thread?   

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I trust this has been good 2016 year end Holiday fun.