USA Trains: NW-2 Modifications & Repair page:
11/27/2010
Wheel not turning/grinding sound: Damaged/stripped axle gear:
If your engine has a grinding sound when running and/or the axle appears to spin freely when not on the track on it's side you likely have a damaged/stripped axle gear. To inspect, put the engine upside down and remove the six bottom screws on the bottom of the motor block and lift the cover plate off.
(Note: NW2 motor blocks only have 4 screws and not 6 like shown in the below example.)
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A stripped gear will be very apparent as can be seen with the axle on the left.
(Note: NW2 axles only have non-traction tire axles and do not have bronze friction bearings as the examples show below.)
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In the cases where I've seen accelerated wear or stripped gears, they've all had inadequate grease lubrication. Those that did have proper lubrication had very little to no noticeable gear wear. Ensuring your motor blocks are properly greased will go a long way to ensuring they don't strip out.
Photos of gear wear due to lack of proper gear lubrication:
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See Traction tires: Should you use or eliminate them for more discussion on axle/gear failure.
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6/8/2011
Wheel not turning/grinding sound: Damaged/stripped axle gear (Caused my worn out motor bearing)
As noted above, if your engine has a grinding sound when running and/or the axle appears to spin freely when not on the track on it's side you likely have a damaged/stripped axle gear. (See above for disassembly steps and photos)
To check to see if your motor has a failed bearing, once you have the bottom plate off the motor block, look to see if either axle has a stripped gear. (A stripped gear will be very apparent as can be seen with the axle on the left.)
(Note: The example for repair below has incorrectly had the original non-traction tire axle on the right replaced with a traction tire version and has not been greased.)
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Once you've confirmed there is a stripped gear, remove that axle and use a pair of needle nose pliers to check to see if there is any up and down play on the motor shaft. When the bearing is worn out the shaft can get far enough out of alignment to lose contact with the gear causing it to strip and fail prematurely. If you have stripped gears you MUST check for this as well as a new axle/gear will quickly strip out.
Example of failed motor with worn out bearing:
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Video: USA Trains (2 axle failed motor bearing):
Note: if the video skips, right click on the link and select "save target as" and save it to your local drive, then play it.
Select the version / quality you want to download:
- Failed motor bearing #1 - 0:26 mins - Example of
failed motor bearing
- 22MB/7000kbs - YouTube 1080p HD
To help slow the rate of wear it would be a good idea to periodically put a small drop of oil to lubricate this point on both sides of each motor.
Once failed, the only solution to fix is to replace the motor. If a replacement motor isn't available from USA Trains you will need to buy a whole new motor block which costs around $45.00
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11/27/2010
Wheel not turning/spins when under load: Cracked axle gear assembly:
Engine wobbles when running: Cracked axle gear assembly:
If your engine either: 1) has a wobble when it runs 2) has a wheel that doesn't turn under load or 3) can by spun manually by hand with the engine stopped, you likely have a cracked axle gear assembly. See below for an example:
(Note: NW2 axles only have non-traction tire axles and do not have bronze friction bearings as the examples show below.)
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To inspect, put the engine upside down and remove the four bottom screws on the bottom of the motor block and lift the cover plate off.
(Note: NW2 motor blocks only have 4 screws and not 6 like shown in the below example.)
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A cracked axle gear end can sometimes be seen immediately but if not, removal of the axle in question may be required by just lifting straight up. (You will either need to pry the truck side frames out a little or unscrew one of the truck frame sides and just remove the motor block completely.) Note that reinstallation of the axles will be more difficult with the motor block completely removed from the engine.)
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If you find the gear axle end is cracked you will need to order a replacement from USA Trains. www.usatrains.com
See Cracked axle ends / Stripped gears for more discussion on axle/gear failure.
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11/27/2010
Worn side bearings (important lubrication point):
If your USA Trains diesel gets much run time or you've added extra weight for additional traction, you're going to have to periodically inspect the truck's friction bearings on the ends of the axles for signs of excessive wear. (Particularly on the three axle truck engines, the ones on the center axle.) This is the point where the weight of the engine (and pull forces) are transferred from the locomotive body to the drive blocks. Because of the situation, you will need to make sure you keep these bearings well lubricated or you can quickly experience excessive wear as in these cases below.
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If you have a case such as the one pictured on the above right, you can extend the useable life by taking a pair of pliers and rotating the bearing 180 degrees. This will expose the other end of the bearing to wear. Eventually however the entire small bearing sub-assembly plate will need to be replaced. The insert bearing itself is flanged on the backside adding to the difficulty of removing just the bearing alone if a suitable replacement could be found.
This is one area I feel needs to be redesigned by the manufacturer. If the axle end shafts were enlarged to better fit the side bearing it would make the pressure points much less severe and thus reduce the rate of wear. Another option would be going with ball bearings which would eliminate the problem completely. More reasonable a fix however is to have weight transferred to the motor block by the adding of an insert between the top of the block and the truck frame. This would transfer weight directly to the motor block and shift some (if not all) of the wear to the inner axle friction bearings. This will be a point of future work on my part to improve upon the design.
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11/27/2010
Power pickup problems: Worn/severed wheel power pickup rods:
If you are having engine power pickup problems (especially if you've removed the power pickup sliders) you may have worn out/severed wheel power pickup rods. If the rod severs completely as the one shown below in the red then you will loose power pickup from that axle end.
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This is another reason to keep you power pickup sliders. If you have problems with sliders shorting on 19.5 Degree crossovers (see: 19.5 Degree crossover modification to eliminate the risk of electrical shorts from engine power pickup sliders) or catching on switch frogs (see: Sliders getting caught in switch frogs. (Particularly #6 switches))
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11/27/2010
Cracked axle ends / Stripped gears:
Regarding the issue of cracked & stripped gears, I recently had to repair 9 USA Trains 2 axle truck engines due to cracked gear axle inserts & stripped gears and found the following:
32 axles (out of a total of 36) needed to be replaced
All 32 failed axles had split gear axle inserts
17 of the failed axles had traction tires
15 of the failed axles did not have traction tires
Of the 17 with traction tires, 6 had stripped gears (all of which had split gear axle inserts)
Of the 15 without traction tires, 4 had stripped gears (all of which had split gear axle inserts)
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These results proved that the root cause of the axle failures wasn't because of the application of traction tires, it is due to poor design of the plastic gear, material & associated plastic insert holes for the axle ends. (i.e. the gear axle insert holes are too small causing the metal drive axle to cause the plastic to split over time) The real long term solution is the plastic gear needs to be redesigned to have a stronger side wall (thicker) and a hole a little larger than what is currently used. Of the most likely cost effective solutions they would likely implement, I would be a proponent of using a fitting less snug (reducing the outward stress on the plastic gear axle insert hole) and the use of either an epoxy or key to keep the axle from spinning in the hole. For any 2 axle USA Trains engines I ever personally own, I will open up the axle hole on the gear and epoxy/glue them in place.
It should be noted that two 3 axle USA Trains engines were also repaired and none of the axles had split gear axle inserts or stripped gears (and those were traction tire equipped engines). Inspection of the 3 axle gear axle inserts seems to show a stronger design and I would assume a more properly fitting axle insert hole.
Regarding the stripped gears, I found those that had accelerated gear wear or stripped gears had inadequate grease lubrication. Those gears that did have proper lubrication had very little to no noticeable gear wear. Ensuring your motor blocks are properly greased will go a long way to ensuring they don't strip out. However this alone won't prevent them from eventually needing to replace them as the axle will most likely fail due to the gear cracking long before the gear finally strips out.
Photos of gear wear due to lack of proper gear lubrication:
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With large number of failures I've seen USA Trains must know about the design problem because of the sheer number of replacement wheels they sell as repair parts. We may not see a part redesign as it may be in their best interest profit wise to continue to sell replacement parts rather than fix the actual problem.
While the NW2 doesn't have traction tire axles, the larger issue of cracked axle ends and stripped gears is still relevant.
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