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This article was written for The 101 Association Repair and Overhaul Manual.

 The Splitdorf DU-7 Generator
Repair & Overhaul

By Steve Blancard


    All 101s up until the inception of the Auto-Lite GAS-4102 generator in 1931 used the Splitdorf DU-7, counter-clockwise rotating generator. The DU-7 was announced by Indian as "standard equipment on all models" in Service shot #15, dated March 5, 1928. The 101 Scout began production on March 30, 1928, less than a month later.  Service shot #41, dated January 26th, 1930 discusses the Auto-Lite generator used on "various models of Indian motocycles". IMPORTANT NOTE; This service shot is apparently dated wrong. It should be dated January 26, 1931 (one year later!). After a lengthy discussion with George Yarocki and in light of the sequential numbering and dates of Service Shots before and after this one, it looks as though the original Indian typist slipped by one (very important) digit.
1931 models began production in March or April of 1931. Considering Indian's policy of "No yearly models, but constant improvements", and service shot #41, the last month or two of 1930 101 production may have used the Auto-lite generator. I’ll caveat this statement with Indian's well known practice of using up parts on hand. It is possible that DU-7s were still used after January of 1931. Based on the available Indian and Splitdorf documentation, all 101s built through January 26th, 1931 probably used the Splitdorf DU-7, after which the Auto-lite-GAS 4102 would be correct.

    Splitdorf manufactured at least 13 different motorcycle generators. The DU-7 is easily distinguished from its predecessors by a larger cutout cover and aluminum commutator head, visible with the cover removed.

The DU-7 cap is stamped:


    All Splitdorf generators can be identified by the model number stamped on the cutout cover. But covers were easily lost and often replaced with whatever was available. Look for the aluminum commutator head to be sure its a DU-7. Rotation on all DU-7s is indicated by a small arrow stamped into the drive end of the main body, approximately opposite the terminal post. The 101’s generator rotates counter-clockwise, thus the arrow should be pointing to the left when looking at the pulley end.

 There are at least five DU-7 variants. These include:
DU-7, Counter-Clockwise rotation -  For Indian 101 Scout and Prince.
DU-7, Counter-Clockwise rotation - For Henderson KJ, KL.
DU-7, Clockwise rotation - For Indian Ace/401/402
DU-7, Clockwise rotation - For Cleveland (possibly marked "DU-7C"). This one uses a unique body assembly.
DU-7H, Clockwise rotation - For Indian Chief. This model is gear driven from the engine's timing gears. It uses a 1-1/2" long drive shaft instead of the 1" shaft used on other models.

    The only difference between the Indian DU-7 and the Henderson DU-7 is the 1/4”-24 threaded boss located on the drive head (behind the pulley). Many 101s I've examined have this boss on their generator. The Prince uses this boss to attach the belt guard, on the Scout it is simply not used. There are two possible explanations: 1) When Indian ordered the new DU-7s in late 1927 they decided to use the same generator on both the Prince and 101 Scout. Or 2) When the Prince was discontinued Indian had a lot of their DU-7s on hand and decided to use them up on the 101.

    Field Coils: The field coils are wired in series. When looking at the commutator end, the left hand lead goes to the top (positive) brush, the right to the adjustable brush. Remove the leads from the terminals. Using an accurate ohmmeter measure the resistance through the two coils. If they read 4-6 ohms, and are not grounded they are good. Inspect for worn or frayed wires and coils wrapping. If the wiring is worn, carefully cut off and solder on new leads. If you remove the field coils and pole shoes, its a good idea to mark them first so they can be replaced in the exact same position. When putting the pole shoes back in, it is imperative that they be exactly parallel to the armature axis. There is only about .015" clearance between the armature and pole shoes on either side. If the shoes are cocked at all, the armature will strike them. In addition, as the armature heats up in use it expands, further reducing clearance.

Above is the wiring diagram for a Splitdorf generator.
Counter clockwise rotation is on the left, clockwise rotation is on the right.

     Armature:  The armature is the heart of the generator. In order to thoroughly test it, a growler is required. A growler is used to detect shorts in the windings. The growler generates current in the armature by creating alternating electromagnetic fields around it. These fields simulate those developed by the field coils during actual operation when the armature is spinning inside the generator body. If you do not have a growler I recommend taking your armature to good Starter/Alternator/Generator shop for testing.  However a couple basic checks can be performed with a good multimeter;
    Check for Grounds: Set your meter to check continuity or resistance, then touch one lead to the shaft the other to one of the commutator bars. It should show infinite or open. Check each commutator bar all the way around the same way. Little or no resistance indicates a grounded coil or commutator bar.
    Check for Opens: Take your leads and touch them to two different commutator bars. You should show good continuity or .5 - 2 ohms. Check bar to bar all the way around. If you show no continuity or very high resistance, there is probably an open in one or more of the windings.
    If these tests indicate a problem, don't despair, the armature can be rewound. In fact the entire commutator can be replaced if necessary. However this may be costly because they must be done entirely by hand. Often, the armature will test O. K, but in the long run it may be worth the extra expense of a rewind for the added reliability.  There is one other problem that may occur. Its called a "Flying Short". This means the armature tests fine on the bench. But when it's spinning at say 2000 rpm it shows an intermittent short caused by centrifugal force shifting the coils and causing them to short or ground. This type of problem can be very elusive and frustrating to isolate. If this appears to be the case, and all other possible causes (e.g. worn brushes, frayed wiring, dirty or rough commutator etc.) are eliminated, it's time for a rewind.

    Commutator: After testing, the commutator should be turned (trued) on a lathe and the mica insulators (between the commutator bars) undercut with an undercutting tool about .050" deep. I follow this up with a final polish with a strip of 320 grit wet/dry paper. Thoroughly clean the commutator of all grit and residue afterwards.

    Bearings:  Fortunately, bearings for the DU-7 are still available. The originals are thrust type "Torrington T-8" (commutator end),"Torrington T-13" (drive end). Modern equivalents are available through bearing supply houses. These are known in the trade as "magneto" bearings. It is very important to properly set up the endplay on these bearings to .001"-.004". Endplay is adjusted by small shims (.003" and .005" may have been used) located behind the drive end inner race - don't loose them. I've found modern bearings may be a few thousandths wider than originals. Often (but not always), when putting in new bearings, removal of 1 shim gives me the proper end play. Excessive end play can allow the armature to move side to side causing it to strike the pole shoes.

    Brushes: 1/4" x 5/16" x 1/2" carbon. I know of no exact replacement for the originals. However brushes designed for small electric power tools can be used. Although they are designed for 120 volts, with some minor modification, will work very well. The seating end of new brushes should be contoured to match the circumference of the commutator to ensure full contact.

    Hardware: All hardware on the DU-7 is standard thread sizes (except the 1/4 - 24 threaded boss which is not used). The two 6 x 32 end cap screws, three 8 x 32 drive head screws and their lockwashers are blued, not nickeled as were those of previous Splitdorf generator. The 1/4 x 20 pole shoe screws are nickeled as is the pulley, it's nut and lockwasher and the Gits oiler. A very close replacement for the Gits oiler is available from McMaster-Carr. The 10 x 32 terminal post and nuts are brass. The large flat washer on the post is copper.
    Felt seal: There is one felt seal located between the commutator bearing and the commutator. This is important to keep lubricant away from the commutator and brushes. It is 3/4" OD x 15/32" ID x 1/8" thick.
 Fuse: There is a 3 amp fuse located on the commutator head to protect the field coils. Carry a couple spares in your toolkit.

    Generator bodies were plated to ensure good electrical contact with the mounting bracket. I've observed some plated with tin, others with nickel. This is rarely seen on surviving generators due to the rapid deterioration of the plating. However, it is readily visible in period photos and Splitdorf literature. The ends of the body were then painted gloss black, approximately 1.2" from the commutator end and .5" from the drive end, leaving a plated center stripe where the mounting clamp attaches. The cutout cover and drive head were also painted gloss black.

    The cutout relay is a device used to prevent the battery from discharging back through the generator when the armature is not rotating fast enough to produce sufficient current. The DU-7 used an improved electrical cutout, located under the end cover. Don't assume that any Splitdorf generator with an electrical cutout is a DU-7. The earlier "A-10" electrical cutout used on DU-5s is not the same as the DU-7's cutout. Indian service shot #35, dated November 5th, 1929 provides detailed adjustment procedures for the DU-7 cutout and is an excellent reference. Contact points should be set at .015 - 020". The shunt windings of early DU-7 cutouts were prone to vibration damage. In late 1929 Splitdorf offered free replacement of the defective cutouts with a more durable unit. The replacements were all stamped on the base with a date. The early cutouts were not dated. One final note on cutouts; Other than cleaning and adjusting the points, follow the old proverb "If it ain't broken, don't fix it". They are the Achilles heel of the generator and are easily damaged.


    Adjustment is easy, however the actual output must be tailored to each motorcycle. Amperage is increased by loosening 2 screws clamping the adjustable brush holder, then moving it in the direction of armature rotation (clockwise looking at the commutator end), then retighten the screws. Ideally, the generator should provide a positive charge of 1 to 1-1/2 amps to keep the battery charged (just like a trickle charger). If most of your riding is during daylight hours, you'll probably want to adjust the generator output with all lights off. However, if you do a lot of night riding, adjusting the output with the lights on, and always riding with them on may be preferable. If available, use a high quality ammeter when adjusting output current. While adequate for daily use, the original equipment ammeter is not accurate enough for precision adjustments. If the generator does not provide sufficient current to meet demand, current will be drawn from the battery as well as that supplied by the generator. Adjust generator output to meet your electrical system's needs - but no more.
 When properly restored, the Spltidorf DU-7 will provide many more years of reliable service. Good luck!


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