Swing Arm Differences

[kp]

Bo recently identified a difference in the chain adjuster guide marks on early Sandcast swing arms. Early arms have notches stamped into the axle receiver section whereas the later markings are cast into that receiver section. As always, photos tell the story.
We have no knowledge of when this early type ceased so I would ask members to let us know what type they have on their machines.

[kp]

We have advice that frame 166 has an early arm fitted. Any higher bids please

[Steve Swan]

We have advice that frame 166 has an early arm fitted. Any higher bids please

232's are cast.  are these notches uniformly stamped or are they a hand operation?  i was under the understanding if i recall correctly that Bo said these graduated markings were filed.

[markb]

I have checked my swing arms. #97 did not have grooves. I did find differences in my swing arms however. The first pic shows skinny ridges.


This pic shows fat ridges. This is the way the later swing arms look. Subtle difference. I didn’t know of the grooves until this week. Steven V. had emailed me about this distinction.

[kp]

Mr Swan, to me the notches looked stamped and are very uniform in depth and spacing
Mark, the areas marked also look to be different. Is your swing arm original to 97. I know that's a "how long is a piece of string" question

[markb]

Is your swing arm original to 97.

To accurately answer your question I have the swing arm that was on 97 (with the skinny markings). I have no reason to believe that it wasn't the original. Unfortunately the one that is on 97 now is the one from 1553. It was in much better condition than the one from 97 and looked the same to me (I did not notice the difference in the markings) so I decided to use it instead. Now that I'm older and wiser  I realize I should have used the original. That will be one of my next projects. Does anyone else have examples of the skinny marks?

[markb]

Throwing in my opinion about the notches, I believe they are definitely machined.

So we have evidence that at least a few of the early swing arms had notches and that it is a very rare feature. It is a bit surprising that 97 doesn't but it is possible it was changed. Or it is possible that the skinny marks are also a rare distinction. I'm thinking about making a reproduction notched swing arm out of a later one. Which brings up two questions. Would anyone have an issue running a notched swing arm on 97? More important does anyone have an early swing arm with skinny marks?

[Steve Swan]

Throwing in my opinion about the notches, I believe they are definitely machined.

So we have evidence that at least a few of the early swing arms had notches and that it is a very rare feature. It is a bit surprising that 97 doesn't but it is possible it was changed. Or it is possible that the skinny marks are also a rare distinction. I'm thinking about making a reproduction notched swing arm out of a later one. Which brings up two questions. Would anyone have an issue running a notched swing arm on 97? More important does anyone have an early swing arm with skinny marks?

Mark, you could easily make notches!  how would you handle the date code on a modified arm?

[markb]

Hmmm. That's a good question. Doing that would seem to get into the area of being (more?) deceptive. I will have to take a closer look at the numbers on my arms. One I wasn't able to find any yet. Where should I be looking?

[markb]

What do you have for date codes on swing arms? I didn't find numbers that looked like date codes. #97 has a 6, #576 has an 8 and #1990 has a 23. I guess #97 could be a 6 or 9 but oriented the same way as #1990 it would be a 6. I'll post some pics when I get a chance.

[Wayne]

I’ve been following this thread and was going to chime in as I remember the “8” stamp on 576’s swingsrm.