Note: For more specifics on K models , search the Harley K Model site.
You can also download a PDF of their frame and casting specific information by clicking the link HERE.
General K Model information is listed below for differentiating those from Sportster frames.

(page under construction)

The easiest way to tell if you have a K or KH (52-56) and not a Sportster frame at a glance is to look at the top motor mount bracket, also called the “engine steady.” ¹⁾

• K and KH model top motor mount bracket is a cast piece and is open to either side. Some K model top motor mounts have casting numbers. Some do not.
  
• The Sportster bracket (from 57-76) is made from stamped steel and looks like an open-sided box on the right side.
  
  • 1957-1966 Sportster top (center) motor mount bracket has a small “pill” shaped hole through the center.
  • 1967-1976 Sportster top (center) motor mount bracket has a larger more “square” hole through the center.
    However, there were some early 1967 XLCH carry over frames that did come with the early top mount.
• 1977-1978 Sportsters do not have a center welded motor mount bracket but has two mounting points on the top (top front and top rear).
  • The top front bracket (16265-76) is an “L” shaped piece with 3 mounting holes bolted to the engine and the neck.
    It attaches to the front two rocker cover studs and under the frame neck by a 5/16“-18 bolt into a threaded hole on the bottom of the neck
  • The top rear motor mount on the backbone is a 5/16” ID welded tube in front of the seat bracket.
• 1979-1981 Sportsters use the same mounting points as in 77-78 except the top rear mount is in a different spot on the frame.
  • The top front bracket (16265-76) is an “L” shaped piece with 3 mounting holes bolted to the engine and the neck.
    It attaches to the front two rocker cover studs and under the frame neck by a 5/16“-18 bolt into a threaded hole on the bottom of the neck.
  • The top rear motor mount on the backbone is a 5/16” ID welded tube in front of the rear tube welding points on the backbone.
• 1982-1985 Sportsters went back to using a welded center motor mount bracket instead of a rear and still kept a top front motor mount.
  • The center mount is welded piece of steel that's bent at 90° on the two bottom bends (box shaped on bottom without sides).
  • The top front motor mount has 4 bolts and attaches to both the rocker box and to two 5/16“-18 threaded holes under the neck.

^{2) 3) 4)}

^{5) 6) 7)}

Neck Casting Numbers:

It is said:
On the neck web of an early Sportster frame, you should find a casting number. ⁸⁾

• Casting numbers ending in -52 are for 1952-1953 K Model frames.
  Possibly 52 & 53 Ks used non welded -52 neck casting frames.
• Casting numbers ending in -52A are for possibly L1954-E1955 K Model frames.
  Possibly 54 Ks had welded -52 neck or -52A neck castings.
• Casting numbers ending in -56 are for 1956-Up K Model and XLH Sportster frames.
  • Early 1956 K neck casting does not have a “stem ridge” (diagonal line extending thru the stem).
  • Late 1956 K and 1957-Up XLH casting does have the “stem ridge”.
• Casting numbers ending in -58 are for XLCH frames.

VIN Numbers on Frames:
Click Here to reference Motor and VIN numbers in the Sportsterpedia.

• 1957-1969 models do not have any VIN numbers. The frame has casting / part numbers in many places.
  But the only type of serial number for the purpose of ownership was the numbers stamped into the engine case.
• 1970 frames:
  In the 70s, Harley started putting the VIN on the right down tube (from then on the bikes were titled by the frame instead of the motor).
  If your frame has a VIN on the neck, it was made in the seventies or later.
  Reportedly some 1969 models received a blank boss on the neck but did not come with a VIN stamped there.

Seat Bracket:

• 1957-1966 XL, XLH and 1958-1969 XLC, XLCH will have the older style seat casting with the seat bracket “Leaning” forward.
• 1967-1972 XLH, 1970-1972 XLCH will have the seat casting with the “Pyramid” shaped seat bracket.
• 1973-1978 Sportsters no longer use steel casting for the seat mount.
  It was replaced with steel straps covering the each side of the frame tube with open holes to hold the support for the seat. ⁹⁾
• A steel bracket assembly is welded to the backbone.
• 1979-1981, the frame changed drastically in the area of the seat and includes a sub frame assembly in the rear behind the seat posts.
  The newly designed oil tank that doubles as a battery tray sits inside the sub frame.
  The seat bracket changed to more of a wide hook instead of a fastened connection attached facing the rear.

^{10) 11)}

^{12) 13)}

1965-1966 XLH, 1965 XLCH Coil / Regulator Casting:

• 1965 XLH frame had a special location for the spark coil.
  The right side seat casting was modded to include a flat area at 45° with two threaded holes for the coil bracket.
  The angled bracket is bent to run under the frame to the left side where the coil is attached.
• 1965 (only) XLCH used Bosch 12v regulator that was mounted between top of the horseshoe oil tank and the frame. ¹⁴⁾
  The right side seat casting was modded to include a flat area at 45° with two 1/4”-28 threaded holes to affix the regulator bracket.
  It used a 1 year only bracket that attached to the “one year only” (i have seen them on 66 ch also) under-seat frame casting.
  For 65 only, the regulator moves away from the top of the generator and is actually bolted above the tool box, left hand side hence special frame bracket and/or moded casting. ¹⁵⁾
  

Earliest known appearance according to the K Model site is April of 1964. Present through 1966 on XLH and through 1969 on XLCH.
Even though the casting began to appear on frames in late 1964 in anticipation of the new mounting locations;
The regulator wasn't mounted there until the 1965 model year when the switch was made to the 12v system. ¹⁶⁾

¹⁷⁾

Oil Tank Bracket:
1966-1969 XLCH frames have the “Lunchbox” oil tank bracket under the seat casting.

• 1966-1971, the angle bracket is welded to the seat casting with the inside angle facing the front.
• 1972-E1973, the angled bracket (62554-72) is bolted with two bolts under the seat casting and the inside angle faces the rear.

¹⁸⁾

With the introduction of the overhead valve Sportster in 57, Harley went to the letter-number format on the right side of the seat casting. ¹⁹⁾
The date code reflects when the frame was made, not when bike was assembled. ²⁰⁾
Therefore it is yet just another tool to distinguish between year models.

1970 and up frames still have casting numbers but they are not normally used to distinguish the year of the frame.
A VIN number is stamped into the neck and that is what determines the year model in the legal sense.
Of course when mods have been done to them, further discover will have to be done.

Generally on 1969 and prior models, the seat casting ear for the gas tank mount on right hand side, you'll see a letter and digit.
The letter is the month, the digit is the year. Example; C6 = March of 1966, , C7 = March 1957 or March 1967 frame.
Sometimes the code is stamped the other way around (letter/digit or digit/letter).
You can distinguish the 57-59 frames from the 67-69 by the seat castings, which are quite different.

The date code may not precisely ID the whole frame but it's a tool as are other ID methods described on this page.
The year certain models were introduced for instance;
1957 XL only model produced.
1958 XL, XLH, XLC and XLCH were the street bikes produced.
1959 XL, XLH and XLCH were the only street bikes produced.
So if you have a J7 XLCH frame (XLCH wasn't made in 1957 so) it is an October 1967 date code which dates it being made in the 1968 production year.

In the first example pic below, a J7 on an XLCH frame would indicate 1967 since XLCH wasn't made until 1958.
In the second pic, the A9 was further diagnosed to a 1969 frame.
The third pic below is of a 6B stamp which is the same as B6 - Feb. 1966.
^{21) 22) 23)}

Attachments to XL, XLH Seat Posts:

• 1957-1964 XLH frames:
  • There are 2 bosses on the left post for mounting the coil and a “Wedding Band” strap on the right post for the oil tank bracket.
• 1965-1966 XLH frames:
  • There are three bosses on the left seat post (two for mounting the coil with the third being for fastening the top voltage regulator mount.
• 1967-1969 XLH Frames:
  • There is one threaded bung welded on the upper right seat post (rear) for attaching the oil tank via a rubber mounting stud.
    The left seat post has only one threaded bung welded lower (left side) to attach the battery tray via a rubber mounting stud.
    Also on the left post is a two hole threaded plate welded up closer to the top for a two wire terminal strip for tail light wiring.
    (both +wiring with tail light grounded to frame).
• 1970-1972 XLH frames:
  • The welded boss on the left post for the two wire terminal strip was replaced by a larger one piece channel placed on the lower end for mounting the battery box.
    There are 4 square holes in center of the channel and 2 threaded holes (1-top and 1-bottom)for the battery tray.
    The top hole is not used for the XLH battery tray but is for the XLCH battery tray.
    The 4 square holes get plastic anchor nuts and screws for attaching tail and turn signal wires (all +wiring with components individually grounded to frame).

Attachments to XLC, XLCH Seat Posts:

• 1958-1965 XLC, XLCH have no bosses or brackets for coil or regulator mounts. ²⁴⁾
  
• 1966-1969 XLCH frames:
  • 1966-1969 CH left seat post has two regulator mounting tabs off the back of the post. ²⁵⁾
    
  • 1967-1969 CH also has a (two terminal) wiring block for the tail light welded below the bottom regulator mounting tab.
  • 1966 CH has no terminal block boss below the regulator mounting tabs.

^{26) 27) 28)}

Straight or Doglegged Posts:

• 1957-1966 XL/XLH and 1958-1969 XLC/XLCH models all have basically straight seat posts.
• 1967-up XLH and 1970-up XLCH models have a dogleg (or kick back).
  • In 1967, Harley introduced the first electric start Sportster (two years after the Electra Glide). ²⁹⁾ Only the XLH model got the upgrade.
    In order to accommodate it, the seat posts had to be modified to make room for the electric start motor and a much larger battery.
    So the 1967 XLH had a whole new frame with a big battery, voltage regulator behind the battery and a coil under the seat. ³⁰⁾
    
  • In 1970, the XLCH was built using a battery for the first time (smaller battery than the XLH).
    The XLH and XLCH now shared the same need for the seat posts to be kicked back to accommodate a battery.

^{31) 32)}

• 1957-1976 lower tubes (both) are straight tubes.
  
• 1977-Up lower right tube is notched to allow the (new in 77) gerotor style oil pump to be removed and installed without removing the engine.

^{33) 34)}