USA Trains: SD70 Repair/Modifications page:

 

 

 

 

 

 

 

11/27/2010

 

Wheel not turning/grinding sound: Damaged/stripped idler gear:

 

 

If your engine has a wheel that isn't turning when power is applied or is making unusually loud noises or grinding sounds, you may have a damaged/stripped idler gear.  To inspect, flip the engine over on it's back and unscrew the ten screws circled.

 

 

 

Then, individually inspect the gears on the idler gear (including the axle gears).  (There are three idler gears per 3 axle motor block.)

 

 

 

You may find the gear either stripped or damaged. (In this case, damaged)

 

 

Replacement idler gears can be purchased from USA Trains (www.usatrains.com) directly for $4.95 

 

 

 

 

 

 

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11/27/2010

 

Wheel not turning/grinding sound (Pivoting end-axle):  Spun universal end-joint / loose worm gear:

 

Wheel not turning/grinding sound (Pivoting end-axle):  Spun universal end-joint / loose worm gear

If your engine has a wheel that isn't turning when power is applied or is making unusually loud noises or grinding sounds, you may have a damaged/stripped idler gear.  To inspect, flip the engine over on it's back and start by unscrewing the four screws circled.

 

 

 

Then inspect the idler gear, axle gear and worm gear.  (In this case you can see the worm gear out of position and loose in the motor block housing.)

 

 

 

If you find the worm gear loose and out of position, the cause is likely to be the plastic universal on the back-end of the worm gear shaft that has spun loose allowing the gear to slide out of position enough to fall out of the front friction bearing.  To fix, you will need to remove the entire motor block from the engine to gain access to the affected parts from the top.  Remove the four screws holding the metal slide guide above the pivoting axle.  Then remove the four screws on each side of the truck frame and carefully pry the truck frames off.  Then remote the block and unscrew the screws in the top of the motor block.  Once in inside you will have access to the worm gear and plastic universal joint ends.  Inspect to see if the worm gear spins inside the universal gear end.  If so you will need to either replace or attempt repair with a strong adhesive like super glue. 

 

(The pictures highlighted in red show the ends that go together and that have spun loose.)

 

 

 

If you attempt a repair, you need to ensure that you glue the universal far enough out on the end of

 

 

 

Replacement idler gears can be purchased from USA Trains (www.usatrains.com) directly for $4.95 

 

 

 

 

 

 

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11/27/2010

 

Wheel not turning (Pivoting end-axle): Stripped plastic universal joint:

 

 

If your engine has a pivot wheel set that isn't turning when power is applied, is making unusually loud noises, or fails to turn when under a load, you may have a stripped plastic universal joint.  The worm gear shaft has a plastic universal joint with a keyed end on it.  This keyed end fits into a receiver on the flywheel.

 

 

End that fits on to the flywheel side.

End that fits on to the pivot axle worm gear. This is the part I've seen stripped/rounded off before.

With the two ends slid together.

 

 

As a fix, the two ends can be permanently super-glued together.  You can still separate the pivot axle from the main truck if need be by disconnecting the universal in another place or taking the pivot worm gear out.

 

 

 

 

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11/27/2010

 

Broken pivot axle support tab:

 

 

If the pivot axle has excessive amounts of play fore and aft at the bottom of the block you may have a broken support tab.  You can attempt a repair but will have to ensure a good job is done using good plastic epoxy or super glue.  In this case I used superglue then backed it up with generous amounts of hotglue to provide additional support.  The fix has held. 

 

 

 

 

 

If repair is not feasible, the only other option is to replace the front pivot motor block assembly.

 

 

 

 

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11/27/2010

 

Worn side bearings (important lubrication point):

 

 

 

If your USA diesel gets much run time or you've added extra weight for additional traction, you're going to keep an eye on 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 and in the case of the center axle, where the majority of the weight is present.  Because of the use of a pivot axle on the three axle truck engines, there are no weight transfer points for the front axle and because there aren't an uneven amount of pressure is exerted on that center axle's bearings.  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. 

 

 

 

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.  Since we aren't likely to see a change from the use of a pivot axle on the three axle truck engines, then some simpler solution should be implemented.  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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08/31/2011

 

Installing Kadee coupler

 

 

There are a couple of options for installing Kadee couplers to your SD70 and which you go with will partly depend on the factory coupler assembly your engine comes with.  (note: all photos in this section are of an SD40-2)

 

 

From the factory, there are two types of coupler mountings you may receive:

 

    -  Sliding mount  - (Allows Fixed Kadee coupler box mounting only, unless parts are ordered from USA Trains.)

                - Fixed mounting results in coupler pulled closer in to engine

                - Coupler height will be slightly lower if fixed with Kadee 787

                - Coupler swing range may be more limited. (possible issue for tighter diameter curves)

 

    -  Swivel mount  - (Allows Fixed or Swivel Kadee coupler box mounting)

                - Fixed mounting can be same as sliding mount above

                - Swivel coupler box allows for tighter turns but results in coupler further away from engine.

                - Swivel coupler mounting with 831 results in proper Kadee coupler height

                - Swivel coupler mounting allows for use on the tightest diameter curves

 

 

Sliding mount photos:

 

 

 

 

Swivel mount photos:

 

 

 

 

Swivel mount:  (Swivel & Fixed mounting options)

 

 

Swivel mount:  Swivel Kadee coupler box install  (Using 831 Kadee)

 

(Note:  This option retains the coupler box swivel function and results in the coupler being further away from the engine.)

 

 

Installation of a Kadee coupler on the existing swivel coupler post is easy.  Assemble an 831 Kadee as shown below. 

 

 

 

Next cut the tab off the end of the coupler post that's on the engine.  See the area noted in RED, cut at the green line, even with existing ridge below the tab.

 

 

 

Finally, attach and screw the Kadee as shown using the existing screw hole and threaded screw provided with the Kadee coupler.  Then reinstall the assembly on the engine.

 

 

 

Final Swivel coupler install photos with Kadee 831:

 

 

 

For comparison:  Example of fixed coupler mounting with Kadee 787

 

(Note the slightly lower mounting.  You will want to bend the Kadee coupler tang up with a pair of pliers to ensure it does not catch on crossovers or turnouts (switches).

 

 

 

 

 

Swivel mount:  Fixed Kadee coupler box install  (Using 787 Kadee)

 

(Note:  This option loses the coupler box swivel function and results in the coupler being closer in to the engine and slightly lower than a standard height gauge.)

 

 

Starting with the swivel coupler mount as shown.  Remove the swivel assembly by removing the center screw between the coupler assembly posts.

 

 

You will be left with just the post with a single hole as shown here

 

 

 

Next, assemble a Kadee 787 as pictured

 

 

 

Grind or sand off back of the coupler box as show to ensure the motor block will have enough clearance.  The install using proper size screw and washer.

 

 

 

Final Fixed coupler install photos with Kadee 787:

 

(Note the slightly lower mounting.  You will want to bend the Kadee coupler tang up with a pair of pliers to ensure it does not catch on crossovers or turnouts (switches).

 

 

 

For comparison:  Example of Swivel coupler install photos with Kadee 831:

 

 

 

 

 

Sliding mount:  (Fixed mounting option)

 

 

Sliding mount:  Fixed Kadee coupler box install  (Using 787 Kadee)

 

(Note:  This option does not have a swivel function (unless needed additional parts are purchased from USA Trains) and results in the coupler being closer in to the engine.)

 

 

Sliding mount assembly:

 

 

To remove, unscrew the two small screws on the bottom on each side.  Then remove the plate and coupler to gain access to the center screw in the middle, then remove the center screw but keep for later use.  You will then be left with the coupler mounting post as shown.

 

 

 

Next, assemble a Kadee 787 as pictured

 

 

 

Grind or sand off back of the coupler box as show to ensure the motor block will have enough clearance.  The install using proper size screw and washer.

 

 

 

Final Fixed coupler install photos with Kadee 787:

 

(Note the slightly lower mounting.  You will want to bend the Kadee coupler tang up with a pair of pliers to ensure it does not catch on crossovers or turnouts (switches).

 

 

 

For comparison:  Example of Swivel coupler install photos with Kadee 831:

 

 

 

 

 

 

 

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11/27/2010

 

Traction tires:  Should you use or eliminate them?:

 

 

This is a point I've seen much discussion on with many calling for the elimination of axles with traction tires over solid metal with the belief that it would reduce the occurrence of: 

 

  • Maintenance (of having to replace worn or dried out traction tires)

  • Cracked gear axle inserts. (mainly on the 2 axle truck engines)

  • Stripped gears

 

 

Based on my own personal experience since 2004, I have become a proponent of the use of traction tires on engines because of the following points:

 

  • Result in a significant increase in the pulling power of a given engine normally requiring the adding of quite a bit of extra weight to gain the same level of pulling power 

    Examples:

    • MTH Big Boy (with traction tires) has average pull force of 7.5lbs with 19lbs of engine weight (not including tender weight)

    • USA Trains Big Boy (without traction tires) has average pull force of 8 lbs with 46lbs of engine weight (not including tender weight)

    • Aristocraft Mallet (without traction tires) has average pull force of 2.5lbs with 15lbs of engine weight (not including tender weight)

  • Results in an order of magnitude increase in pulling force for each additional amount of weight added compared to not having them

  • The reduced overall required weight reduces drive train, gear and rod wear as the engine doesn't have to pull the extra weight up grades

  • The reduced overall required weight reduces bearing wear that on some engines is an issue. (See Worn side bearings )

 

 

 

 

See below on the issues of Maintenance & Cracked / Stripped gears:

 

 

 

Maintenance:  Regarding the need to replace due to wear or dry-rotting, I've found this to not be a problem at all on all of the MTH and USA Trains engines (the two main companies that use them).  Some of my engines are 6 years old (as of 2010) and see no need to replace due to wear or dry-rotting.  I've also had the opportunity to inspect 11 USA Trains diesels (some of much greater age) and none of them were worn out or dry-rotted.  Based on what I've seen, any engines that experience serious dry-rotting may be very early production runs or were just a batch with traction tires that had poor quality rubber.

 

  

 

 

Cracked / 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)

 

17 traction tire axles on left

15 non-traction tire axles on right

6 traction tire axles with stripped gears

4 non-traction tire axles with stripped gears

 

 

 

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 axle 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 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 gain you too much benefit as the axle will most likely fail due to the gear cracking long before the gear finally strips out. 

 

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.

 

 

 

 

In conclusion, based on all the data above and seeing the benefits of actual application of engines with traction tires, I still prefer engines with traction tires over those that don't.  I'm generally always much happier with the pulling performance of those engines that have them compared to those that don't. 

 

 

 

 

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