Serial Numbers

The serial number of your Lightweight is stamped into a raised pad on the left side of the engine crankcase. It’s near the front, and turned vertically. There is no serial number on the frame.

Sometime back in the teens, Harley-Davidson standardized their serial number scheme. The serial number is stamped into the engine. This scheme was used until around 1980 when 17-digit Vehicle Identification Number was mandated by law. The format was (using the example of a Knucklehead: 37 EL 2318)

        37 EL 2318
        |   |   |
        |   |   Sequence Designator
        |  Model Designator
	Year Designator

The Year Designator was always 2 numeric characters.

The Model Designator varied from 1-to-5 alphabetic characters. The first character letter of the model number indicated the basic engine type. An “E” was a 61 cubic inch overhead valve engine. Additional letters indicated variants of the engine or bike. An “EL” was a High Compression version. An ELP was a high compression Police version.

The Sequence Designator was 4 or 5 numeric characters, representing the order in which a completed bike left the assembly line. The first E model off the assembly line in 1937 was given sequence number 1001. The second bike got 1002, and so on until the end of the year. But the Sequence Designator was applied to the basic engine type - not to the variants. So when the bikes started rolling off the assembly line in 1937, they might have been: 37 E 1001, then 37 EL 1002, then 37 E 1003, and so on. The American-made lightweights followed this scheme, with a few interesting anomalies.

Years	M.D.	Name	Description
1948 - 1952	S	Model 125	Single-cylinder two-stroke, generator, 125cc
1953 - 1959	ST	Model 165	Same but 165cc
1953 - 1959	STU	Model 165	STU Same, 165cc, low horsepower
1955 - 1959	B	Hummer	Single-cylinder two-stroke, magneto, 125cc
1960 - 1961	BT	Super-10	Same but 165cc
1960 - 1961	BTU	Super-10	Same, 165cc, low horsepower
1962	BT	Pacer	Same, but Road Model, 165cc
1962	BT	Pacer	Same, but Road Model, 165cc, low horsepower
1962	BTH	Scat	Same, but Off-Road Model, 175cc
1962	BTF	Ranger	Same, but Hunting/Fishing 165cc
1963 - 1965	BT	Pacer	Road Model, 175cc
1963 - 1965	BTU	Pacer	Road Model, 175cc, low horsepower
1963 - 1965	BTH	Scat	Off-Road Model, 175cc
1966	BTH	Bobcat	Road Model

Anomalies - 1962 Engines

Anomalies - Sequence Designators

During the 1960's, Harley played some games with the Sequence Designators. We’re not sure why, but we think it was industrial disinformation. Sales of the lightweights were steadily decreasing, and Harley probably wanted competitors to think they were selling far more bikes than they really were. Perhaps you have a different theory.

In 1960 (an "even" year), serial numbers started at 2001, went to 2999, skipped to 4001 through 4999, then skipped to 6001 through 6488.

In 1961 (an "odd" year), serial numbers started at 1001, went through 1999, then skipped to 3001 through 3587.

This "even/odd" pattern repeated through the end of production in 1966.

We have several other anomalies. In 1959, ST production seemed to stop at serial 3326. But we've recorded 59 STU 5981 and 59 ST 6815. These could be mistakes by the owners reporting them, or even stranger quirks in the numbering system.

Anomalies - U Models

Back in the 50's and 60's, many states had a "junior driver's license" which allowed 14-year-olds to drive motorcycles under 5 Horsepower. These laws were prevalent in the mid-western states. In those days, Go-Karts and MiniBikes were quite popular, and Harley-Davidson tapped the junior market with special versions of the Model 165, Super-10, and Pacer.

The U models had a restricted intake system to drop the horsepower to just below 5, making them eligible for junior licensing restrictions. The 125cc Hummer was already eligible, since it only produced 3.5 hp, but apparantly many people wanted the increased power and style of the Model 165.

The Model 165 STU, produced from 1953 to 1959, had a carburetor with a restricted orifice. The carburetors were designed to be used on different sized engines, and "tuned" for a specific application by using an orifice plate with a opening of the proper size for the application. The STU's orifice plate just had a smaller opening than standard ST's.

The Super-10 (1960-1961) and Pacer (1962-1965) also came in BTU variants. In 1962, the Pacer BTU had the 165cc engine, while the standard Pacer BT had the new 175cc version. It is believed that the 1963-1965 BTU's used the 175cc engine. See the Ranger and Pacer chapters for more on the mix of 165 and 175cc engines in 1962.

The BTU's achieved the "throttling effect" by using a special cylinder head with a restricted intake port rather than a different carburetor.

One anomaly exists with the late 1958 and 1959 STU's. The factory parts book lists Cylinder 16526-58 as Late 58 & 59 - STU (special). The restricted orifice carburetor is listed from 1953-1959. But there are different carburetors listed for standard ST's: one from 1953-1958, and a different one for 1959. Perhaps the late-1958 and 1959 STUs used the special cylinder with a standard 1959 carburetor. This is a matter for further investigation.

MODELS AND PRODUCTION FIGURES

Harly-Davidson production figures are taken from the recent book "The Legend Begins" published by Harley-Davidson. In a few cases, the Club has a recorded serial number which indicates a slightly higher production figure. Number known in existance is taken from serial numbers reported by Club members. More information about the serial numbering scheme is at the bottom of the table.

We think that there are probably double or triple this number still in existence. Some Club members have not reported their serial numbers. And there are many Hummer owners who unfortunately do not belong to the Hummer Club.

APPROXIMATE PRODUCTION FIGURES

YEAR & MODEL	NUMBER PRODUCED		KNOWN IN EXISTANCE		NOTES
	H-D	CLUB	#	%
48 S	10117	10117	90	0.9%	.
49 S	7291	7291	55	0.8%	.
50 S	4708	4708	31	0.7%	Perhaps 5415 made
51 S	5101	5101	41	0.8%	.
52 S	4576	4576	46	1.0%	.
53 ST	4220	4232	54	1.3%	High serial# 5232
53 STU		0	0	0.0%
54 ST	2835	2835	43	1.5%	.
54 STU		0	0	0.0%
55 B	1040	1040	20	1.9%	.
55 ST	2263	2182	27	1.2%	H-D includes STU
55 STU		81	1	1.2%
56 B	1384	1384	22	1.6%	.
56 ST	2219	2119	39	1.8%	H-D includes STU
56 STU		100	2	2.0%
57 B	1350	1230	18	1.5%	.
57 ST	2401	2051	38	1.9%	H-D includes STU
57 STU		350	7	2.0%
58 B	1677	1684	21	1.2%	.
58 ST	2445	2201	36	1.6%	H-D includes STU
58 STU		244	4	1.6%
59 B	1285	1394	31	2.2%	High serial# 2394
59 ST	2311	1895	41	2.2%	H-D includes STU
59 STU		416	9	2.2%
60 BT	2488	2169	34	1.6%	H-D includes BTU
60 BTU		319	5	1.6%
61 BT	1587	1280	25	2.0%	H-D includes BTU
61 BTU		307	6	2.0%
62 BT	1983	745	12	1.6%	H-D includes all HHC-1986 total
62 BTU		62	1	1.6%
62 BTF		186	3	1.6%
62 BTH		993	16	1.6%
63 BT	575	581	6	1.0%	HHC - 1762 total
63 BTU	50	50	0	0.0%
63 BTH	1125	1131	15	1.3%
64 BT	600	600	7	1.2%	.
64 BTU	50	50	0	0.0%
64 BTH	800	800	10	1.3%
65 BT	500	500	9	1.8%	.
65 BTU	50	50	0	0.0%
65 BTH	800	800	14	1.8%
66 BTH	1150	1150	18	1.6%	.