Click Here to reference the Ironhead Engine Case Identification page in the Sportsterpedia.
The engine VIN, also called engine number or serial number, and can be found on a pad in the “V” between the cylinders.
Motor serial numbers are on the left side of the motor from 1957-1969 and on the right side of the motor from 1970-1985.
From 1957-1969, motorcycles were titled to the engine only. Starting in 1970, motorcycles were titled to the frame instead of the engine.
But if your frame and motor were born together the numbers will match (and possibly save you title hassles).
There are also casting numbers as well as stamped numbers in various places on the engine and early frames, but they are not motor numbers.
Casting numbers do not indicate the year of your bike, only the date the part was cast.
For instance, on a 70s bike, there are still quite a few -52 (the first year of the K model) numbers.
(leading the uniformed to advertise all sorts of later model parts as K model parts)
Decoding the motor number / VIN will tell you the year of the motor and hence the gasket set you should buy.
Often, riders add later parts, especially items like transmission doors and oil pumps because the later castings have been improved.
Just because you have a later casting number on a part of the motor does not mean you have a later motor though.
The casting date simply tells you the month the part was cast. This is not the same as the day the assembly was made.
Casting dates can help confirm that factory cases on a 1976 motor were not cast in 1978 for instance.
1975-1985 various engine number locations:
1975 model casting and stamped engine numbers: 1)
Noted serial numbers with their respective dates as stated in service bulletins.
In an effort to date (somewhat) factory issued engine VINs, a list is being compiled below of engine numbers verified through service bulletins.
IF your VIN is listed below (or even before or after dates), it may help deciphering app dates.
The list may also help to establish a range of VINs within specific times frames as defined by the MoCo in the TSBs.
1973 Models | ||
XLH/XLCH | 3A or 4A, 42100H3 to 50000H3 | Produced between October 31, 1972 and March 25, 1973 10) |
FX | 2C 12100 H3 to 19200H3 | |
XL/XLCH | 3A or 4A, 45311H3 to 46787H3 | Described as an initial production of 1973 models 11) |
XL/XLCH | 3A or 4A, 60000H3 to 60130H3 | |
XLH/XLCH | 3A or 4A, 40000H3 to 50772H3 | All 1973 XL and XLCH motorcycle frames will require corrective modification 12) |
XLH/XLCH | 3A or 4A, 60000H3 to 71568H3 | |
1975 Models | ||
XL/XLCH | 3A or 4A, 10000H5 to 51760H5 | Front brake caliper mounting bolt defect showing affected models 13) |
FX | 2C10000H5 to 2C51760H5 | |
FXE | 9D10000H5 to 9D51760H5 | |
FL/FLP | 1A24439H5 to 1A48750H5 | Safety Defect, inspect for wheel spoke breakage 14) TSB issued November 7, 1975 |
FLH | 2A24439H5 to 2A48750H5 | |
FX | 2C24439H5 to 2C48750H5 | |
FXE | 9D24439H5 to 9D48750H5 | |
XLH | 3A24439H5 to 3A48750H5 | |
XLCH | 4A24439H5 to 4A48750H5 | |
1976 Models | ||
XL/XLCH | 3A or 4A, 10000H6 to 55388H6 | Front brake caliper mounting bolt defect showing affected models 15) |
FX | 2C10000H6 to 2C55388H6 | |
FXE | 9D10000H6 to 9D55388H6 | |
XLH/XLCH | 3A or 4A, 31727H6 to 50376H6 | Rear brake shoe linings with defective adhesive bond Produced January 5, 1976 to May 20, 1976 16) |
1977 Models | ||
XL/XLCH | 3A or 4A, 10000H7 to 26346H7 | Front brake caliper mounting bolt defect showing affected E1977 models 17) |
XLT | 2G19844H7 to 2G26346H7 | |
FX | 2C10000H7 to 2C26346H7 | |
FXE | 9D10000H7 to 9D26346H7 | |
XLH/XLCH/XLT | 3A/4A/2G 27940H7 | New breather valve in late 1977 models beginning app October 15, 1976 App date corresponds to VIN listed 18) |
XLH | 3A51694H7 to 3A51717H7 | (24) Produced Friday June 24, 1977 19) |
3A51739H7 to 3A51799H7 | (61) Produced Monday June 27, 1977 20) | |
3A51820H7 to 3A51834H7 | (15) Produced Tuesday June 28, 1977 21) | |
1979 Models | ||
XLH/XLCH | Mixed numbers | Engine numbers from January 9, 1979 to February 8, 1979 were mixed. Click Here to read more on the 1979 Exception |
XLH | 3A10001H9 to 3A12067H9 | Produced between February 15, 1978 and March 22, 1978 22) |
XLH | 3A17502H9-3A17737H9 | Produced in the 2nd week of June, 1978 23) |
XLCH | 4A17404H9-4A17621H9 | |
XLH | 3A56358H9-3A57166H9 | Produced and shipped from 3/22/1979 to 3/30/1979 24) |
XLH | 3A53871H9 | |
3A57901H9-3A57928H9 | Produced and shipped between March 30, 1979 and April 19, 1979 25) | |
3A58103H9-3A58144H9 | ||
3A58406H9-3A58413H9 | ||
3A58528H9-3A58540H9 | ||
3A58541H9-3A58621H9 | ||
3A58664H9 | ||
3A58667H9-3A58707H9 | ||
3A58746H9-3A58789H9 | ||
3A58905H9-3A58937H9 | ||
3A59068H9-3A59087H9 | ||
3A59155H9-3A59204H9 | ||
3A59339H9-3A59378H9 | ||
3A59412H9-3A59429H9 | ||
3A59530H9-3A59560H9 | ||
3A59663H9-3A59670H9 | ||
3A59856H9-3A59870H9 | ||
3A59987H9-3A59046H9 | ||
3A60083H9-3A60103H9 | ||
3A60379H9-3A60410H9 | ||
3A60623H9-3A60661H9 | ||
3A60913H9-3A60935H9 | ||
XLS | 4E58285H9-4E58292H9 | |
4E58665H9-4E58666H9 |
The numbers on the bottom of the cases are commonly called the “belly” numbers or “line bore” numbers. 26)
If your bike has “born together” cases, the numbers on each case half should match.
These numbers have nothing to do with your gasket set or anything else.
Both case halves should carry a set of these numbers that indicate their actual machining date (when the case halves were machined as a pair).
Belly numbers have no relationship to the Serial number (or VIN number respectively) located on the side of the engine.
Belly numbers are stamped the day the case halves are machined (line bored) and paired up.
The motor serial number or VIN respectively happens later after engine assembly.
These two have absolutely no correlation to each other except they can be a dead give away on bogus numbers when they are out of the realm of possibility with each other.
For instance, if you have an early 77 VIN, the bike would have been assembled in late months of 1976.
If the belly numbers show a machining date of April, 1977, at least the red flag is there.
However, it's possible for blown out cases to get replaced with the same VIN but carry a newer belly date code (newer machining date).
So it's not set in stone that the belly numbers will match the app year/production month of the VIN.
Belly numbers were coded beginning with a model digit (7) for Sportsters, year and 4-5 running sequential numbers for the year model:
Model (1 digit)-Year (last 2 digits)-Sequential No (4 or 5 digits)
Each set of belly numbers is stamped on the bottom of each case half and the numbers should match if they were factory issued.
For convenience, Click Here to see the Julian Day Calendar page in the Misc Resources section of the Sportsterpedia.
You can open a pic of a full per-year calendar thru 1985 there and match your belly numbers to find the day your cases were machined.
Belly numbers changed from simple sequential serial numbers to include the Julian Day Code and sequential production number for the day.
HD Model Designation (1-2 digits) - Year (2 digits) - Julian Day of the Year (3 digits) - Sequential Number (3 digits)
These 1975 XLCH cases were machined December 17, 1974 (Julian day# 351). Casting date of Nov. 1974 29) | |
1975-1985 belly numbers on right case bottom 30) |