Repair
Beneath follows an excellent article written by Steve Blancard, giving you an insight of what it is involved in repairing one of these old Splitdorf generators.
IDENTIFICATION
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:
SPLITDORF
MADE IN U.S.A
DU-7
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-7's 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 and 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 101's 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-7's 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-7's on hand and decided to use them up on the 101.
TESTING AND SERVICE
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.
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 multi-meter.
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 OK, 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. It's 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.
REPLACEMENT PARTS
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 lock washers are blued, not nickeled as were those of previous Splitdorf generator. The 1/4 x 20 pole shoe screws are nickel plated as is the pulley, it’s nut and lock washer 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.
IDENTIFICATION
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:
SPLITDORF
MADE IN U.S.A
DU-7
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-7's 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 and 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 101's 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-7's 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-7's on hand and decided to use them up on the 101.
TESTING AND SERVICE
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.
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 multi-meter.
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 OK, 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. It's 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.
REPLACEMENT PARTS
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 lock washers are blued, not nickeled as were those of previous Splitdorf generator. The 1/4 x 20 pole shoe screws are nickel plated as is the pulley, it’s nut and lock washer 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.
By Steve Blancard
