Chainring wobble- bent crank or?

[pixeltaker]

Hi CABERS- I have a chainring on 52 Hornet that I thought was bent because there was a pronounced wobble when spinning. After pulling the chainring off I see it undamaged. I found that the problem was the drive pin on the crank was not allowing the chainring to bolt flat on the drive side of the crank. I bolted up a crank off a newer bike and it did not wobble. In the mean time I added a 1mm chainline spacer to the drive side of the original crank and it does not wobble. So, my question is, looking at the images is my crank bent or? I'm newly obsessed with Schwinns and don't have a frame of reference for a bent crank.

 

[bikemonkey]

First of all - you did a great job explaining the problem with words and pics as well as what corrects the wobble. In my opinion there are only three causes.

#1 - It left the factory with an incorrectly milled drive pin and has always been that way.

#2 - The crank arm or chain ring was replaced at some point with one that is incompatible with the other (for various reasons).

If a side load bent the crank arm it would probably have deformed the chainring and the upper crank arm as well. That portion of the arm between the drive pin and the shoulder is beefy and should have been the last place to deform under stress. I would think the crank arm would be noticeably bent more at the pedal end if it were side loading impact damage that pushed the drive pin downwards.

If it is the original crank and sprocket, I would take them to a machinist and have the drive pin slightly milled.

The third cause is the correct one that I have overlooked but will surely be pointed out as soon as I post this....

 

[pixeltaker]

First of all - you did a great job explaining the problem with words and pics as well as what corrects the wobble. In my opinion there are only three causes.

#1 - It left the factory with an incorrectly milled drive pin and has always been that way.

#2 - The crank arm or chain ring was replaced at some point with one that is incompatible with the other (for various reasons).

If a side load bent the crank arm it would probably have deformed the chainring and the upper crank arm as well. That portion of the arm between the drive pin and the shoulder is beefy and should have been the last place to deform under stress. I would think the crank arm would be noticeably bent more at the pedal end if it were side loading impact damage that pushed the drive pin downwards.

If it is the original crank and sprocket, I would take them to a machinist and have the drive pin slightly milled.

The third cause is the correct one that I have overlooked but will surely be pointed out as soon as I post this....

Thanks for the reply! I'm going to find a shop that can mill it a millimeter. Reason #1 seems plausible. The bike rode fine before disassembly, and with the chainguard one you couldn't see it wobble. I didn't notice it until it was up on the stand ready for new bearings and grease.
Or the third cause is the correct one that has been overlooked but will surely be pointed out as soon as I post this....