Proper frame for my 1957 Sportster

[imcranco]

Can anyone tell me the proper frame for my 1957 motor (57xl1729) I've been told it should us a 1956 K frame by some and others say a 1957 XL frame. Supposedly the very '57s used the late K frames. I would love some in-put. I have a 56 and 57 frame

[EKHKHK56]

What are the date codes on frames? Your Vin # is near middle of the mfg run. Not positive, but I would say a frame dated around early 57 would be appropriate. Erik

[hennesse]

Can anyone tell me the proper frame for my 1957 motor (57xl1729) I've been told it should us a 1956 K frame by some and others say a 1957 XL frame. Supposedly the very '57s used the late K frames. I would love some in-put. I have a 56 and 57 frame

Over in the Technical section, there's an article called "Serial and Other Numbers" - it has info about frame date codes. Your bike was #729 of 1988 produced. Some guesswork about monthly production puts it around January 1957. The frame was probably made 1-2 months earlier, maybe November or December 1956. So your frame date code might be K6 or L6.

We don't know how many bikes the factory rolled out each month, nor do we know exactly how far in advance the frames were made. So maybe the bike shipped in February, the frame made in January (A7). It's all guesswork. What's important is that it is reasonable - obviously the frame could not have been made after the bike shipped. Nor should the frame have been made 9 months prior.

What are the date codes on your frame?

[strong56KH]

Over in the Technical section, there's an article called "Serial and Other Numbers" - it has info about frame date codes. Your bike was #729 of 1988 produced. Some guesswork about monthly production puts it around January 1957. The frame was probably made 1-2 months earlier, maybe November or December 1956. So your frame date code might be K6 or L6

What are the date codes on your frame?

[/quote]

I think you mean 6K or 6L

[JerrryR]

Hi All, as far as 57XLs go we do have some documentation that helps us get a sense for approximate delivery dates to dealerships. The following pictures are of dealer invoices for 3 different 57XLs. The pictures show the VINs, when ordered and when delivered. Working backwards from that we can make a pretty good guess at what months an appropriate frame would be date coded.

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From these invoices I think it would be reasonable to guess that your 57XL 1729 was delivered to the dealership in late November or early December. Backing up a few months from that would put your frame date somewhere around July, August or September?

As far as the frame date codes go it is just legend that in the 1950s versus the 1960s that in one decade the letter (month) we first and in the other the number (year) was first. I have seen and photographed both decades coded both ways. In fact I have seen a number of frames where one of the stamps was done upside down or where one of the stamps is above the other not next to it. Since I can only do three pictures at a time I will post another with the pictures. Hope to see a bunch of you at Davenport. JerryR

[JerrryR]

Here are the frame date pictures. The A above the 6 is a 56K frame, the A7 and the 6K are both 57XL frames.

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[MTaylor]

I've been told that the frames weren't used consecutively. In other words, there was a line of frame for production, and then they might bring in more frames and put them in front of the frames that were already there and they would get used first. This is anecdotal, of course, and we would have to look at the date codes on a lot of known original bikes to be certain, but it seems quite likely.

[Hammie13]

I may be wrong,but it's my understanding that most 1956 K frames were "dimpled" behind the motor mount to clear the rocker boxes on the '57 sportsters motor,as they were not sure how many K's were to be sold/built. They wanted to be ahead of the curve on the motor transition. Again,I may be wrong,but I have a '56 frame with the dimpled top back bone.

[JerrryR]

From the research the OSKRG group did on frames I believe the transition to the "smashed underside" of the backbone took place about in December of 55 or January of 56. My A6 K frame has a smashed backbone underside. If my recollection serves me correctly one of the group has an L5 K frame without the smashed backbone underside. There is a Table on page 10 of the OSKRG Bulletin on frames at Dave's website that has a lot of this information. Everybody have a great day. JerryR

[EKHKHK56]

10-4 on that, my 3 1956s are all flattened under the back bone. When I finally found my first one I thought great, somebody has modified it, but came to find they were factory done. Erik