This article originally appeared in the Winter 2001 issue of the AMCA club magazine "The Antique Motorcycle".

1920's Harley® generators - an overview
From: Perry Ruiter

In his excellent book on restoring VLs, Steve Slocombe claims that the Harley 32E generator "must be one of the best documented electrical parts of all time".  Unfortunately, the same can not be said about the generators that preceded the 32E.  I hope this article begins to shed some light on the generators Harley used prior to the 32E.  The focus will be on JD generators used during the 1920's, with a discussion of the differences between each model and how to identify them, then some overhaul pointers.  If there is interest, a subsequent installment could look at generators used on teens JDs, DLs and early VLs.

Generator models:
Harley Davidson began manufacturing their own generators in the latter part of the 1920 season (earlier generators had been supplied by Remy Electric).  Between then and the end of the JD era (1929) four distinct models had been produced:

(above lines quoted from 1926 parts book, ending years for D models inferred from a 1931 parts book).

The only difference between the model D and D1 generator is in the distributor drive helical gear on the armature.  Generator internals are identical (even the armature itself is identical, just the helical gear pressed on the armature is different).  Gear 1649-18 was used on twins and has four teeth.  Gear 1648-26 was used on singles and has six teeth (gear 1648-30 also has six teeth and is used on 1930 - 1934 singles, but the ID of the gear is increased to accommodate the increased drive end armature shaft size).  Since the model D and D1 generators are so similar, comments below referring to the model D also apply to the D1 unless explicitly stated otherwise.

Generator body and end plate:
The generator body and drive end plate are castings.  There are two general styles of each with the model C being the change over.  Model A and B body castings are "open" at the commutator end and have the commutator end bearing supported by the casting from the top and bottom.  Model C and D body castings are "closed" at the commutator end and have the bearing supported from the center.  The bodies have numbers cast into the bottom between the mounting platform.  I have observed the following:

Fourth mounting hole is drilled and tapped on the model Ds.

At the same time as the body casting style changed, the end plate casting (where the distributor mounts) also changed.  Model A and B end plates, 1555-20, affix to the generator body with two screws.  Model C and D end plates, 1555-24, use three screws.  The screws, 1512-18, are the same screws used for pole shoes.  Model A and B end plates use a grease cup to lubricate the timer shaft.  Model C and later use a flat top Alemite grease fitting.  The grease cup threads are 1/8 NPT.  The grease fitting threads are 5/16-32.  In all cases the threads for the timer base set screw, 1542-20, are 5/16-32.

Generator body tags:
Generator bodies had a small brass identification tag riveted onto one side.  There may have been some overlap, but as a rule of thumb most generator models had their own unique style of tag.  Model A tags differ completely from the Remy tags.  Model B tags have the famous bar and shield logo along with a patent date.  Model C and D tags are similar, but differ from Model B by no longer having a patent date on them (I've also observed a variant of the model C tag with a slightly different style of bar and shield logo).  For the 1928 season tags were eliminated.  1928 and 1929 generators do not have tags.

Commutator end covers:
Here again 1924 was a change over year.  Prior to 1924 the end covers have a J slot cut into the side for a set screw on the underside of the generator body.  There are two styles of these early covers:

Model C and later commutator covers are held on with two small screws through the end of the cover.  The primary difference between model C and early model D end covers is that the model C cover has a large square cut out of the bottom of it to accommodate the generator output wire clamp, 1744-24.  The clamp was redesigned and moved to the underside of the generator on the model D's.

Sometime during the 1928 season an oiler cap was added to the commutator end cover.  This is to get oil into the commutator end bearing without needing to remove the cover.  The oiler was not a common Gits style flip up oiler, but rather the lid was held shut by a spring running up through the center of the oiler body.  The addition of this oiler necessitated a running change to the left bearing cover, 1647-24.  The part number never changed.

The final point worth noting before leaving commutator end covers is that the 1929 models had an external lever on the third brush plate.1929 was the first year with an ammeter fitted as standard equipment.  I assume the intent was that the ammeter would allow the rider, while underway, to reach down and adjust the output to match their needs.  This is a one year only feature.  So, in addition to the oiler, the end cover for the 1929 models had a notch in its edge to accommodate the lever and its movement.

Armatures:
Each model of generator had its own unique armature (save for the D and D1 which shared a common bare armature).  The drive end of the armature shaft has a 5/16-18 left hand thread.  1653-18 is the left hand thread nut used to retain the drive gear (JDH models have a generator drive gear with a recess for the nut and require a different nut, 1653-28, but use the same left hand thread).  The model A and B armatures are similar, but the shaft, at the commutator end, on the model A is different to accommodate the centrifugal cut out mounted there.  The model C and D armatures are also similar.  The difference is the length of the commutator.  The model C commutator has an overall length of 11/16 of an inch and a 1/16 inch spacer on the end before the 1641-24 oil deflector.  The model D commutator has an overall length of 3/4 of an inch and no spacer before the 1641-24 oil deflector.

Overhaul pointers:
Since the thread for the timer base set screw is not a standard thread it's fairly common to find end plates with these tapped oversize.  As the end plate is cast, welding is not an easy repair.  The usual fix in this case is tapping it well oversize and threading an insert in with the ID having the correct thread.

The armature is another area that often needs attention.  The left hand threads on the drive end of the armature are often damaged.  Building the area up with weld and turning new threads has proven a successful method of repair.

To properly test an armature a growler is required, but a couple preliminary tests can be done with just an ohmmeter.  Verify the commutator (copper bars on end) is isolated from the shaft.  Also go around the commutator bar to bar verifying the resistance between any two adjacent bars does not exceed 1 ohm.  Do not fear if your armature fails the tests.  They can be rewound.  Even the commutator can be replaced if it is badly damaged.

The bearings used at either end of the armature are number 201 (modern number 6201) which is a standard bearing size available just about everywhere.  You'll likely get a permanently lubed and sealed bearing which is a nice upgrade.

In general field coils are much more likely than the armature to still be serviceable.  All generators prior to 1930 had the pair of field coils joined together internally by twisting and soldering a bare wire from each together.  The ohm reading for the pair of field coils should be around 4.0 ohms (plus or minus a few tenths of an ohm).  Also make sure the ohm reading between the field coils and the generator body is infinity (eg: the coils are completely isolated from the generator body).  Under the twisted and soldered field coil joint is connection insulator, 1515-20, which is a piece of insulating paper 1 1/2 by 3 inches.  This often becomes aged and brittle and it may be damaged or partially missing.  If your field coils are not isolated from the generator body this is a likely cause.  I always replace it with a new piece of armature slot paper, but any none conductive material should work.  End cover insulation, 1697-26, is also a piece of insulating paper.  It is 7/8 by 11 1/4 inches and fits inside the end cover to insure it does not short against the brushes or brush holders.

When facing the commutator end of the generator, the lead from the right hand field coil is connected to the third brush (the adjustable one in the "top middle").  The lead from the left hand field coil is connected to the positive (left hand) brush.  The right hand brush is the negative brush and it's brush holder should be grounded.

NOS brushes can still be found for all models.  A surprising source of brushes for the 1926 - 1931 models are the Accel brush sets for 32Es (Accel part number 192302).  They have been mistakenly produced in the earlier style.  No doubt Accel will correct this eventually, but I've used several sets over the past year in model D generators.  These should be available through (or even in stock at) most chopper shops.

For model A and B generators the output wire exits the generator through a cable bushing (1742-18 for model A and 1742-22 for model B).  This cable bushing is made from some type of plastic or phenolic.  They are threaded into the generator body and care should be exercised removing and cleaning them.  They are easy to damage.

The bodies and end plates are finished in black paint.  Small hardware is either nickel (Alemite fitting, timer base set screw), cad (grease cup) or parkerized (screws, etc.).

Replacement brass tags are now readily available for all models.

I hope this summary of my notes has proven helpful.  I'm always interested in learning more, so please contact me with questions, corrections, suggestions or new information.
 
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