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What is going on here?

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ballooney

I live for the CABE
Bike: '49 B6

Problem: crank arm will not clear the chain guard.

Outer Measurements between chain stays taken at the drop out (5") and just after the kickstand housing (4 1/4") are the same as another B6. So there doesn't appear to be a bend in the frame after the bottom bracket.

Crank that came on the bike appeared bent so I replaced it with the crank that works fine on another B6. Here is the crank that came on the bike...looks to be a 1" flare when using two straight edges:
bb6671bd58d2121da90e4fe3cff48b33.jpg


Here is a crank that is straight for comparison. Looks to have a 3/4" flare:
ad9b18c175242c82c15f4b59456a01dc.jpg


With a straight crank on the bike in question, here are my clearances:
d6e62779f5f09345295b667805652313.jpg

e091884a4c496b53b65b95f00f60b0e0.jpg


Compared to a B6 with no issues:
9b7b26a2bdfb8d8bd60086619bb59215.jpg

849ab4f6ae8cbfacf46693229af82392.jpg


The B6 with the clearance issue seems shifted in that there is plenty of clearance on the non-drive side but almost no clearance in the drive side. Just the opposite of the good B6.

What got me here? The bike rode oddly under feet like a bent shaft on a pedal. So I started pulling it apart...pedal shaft was straight. Pulled the crank and noticed it was bent...ah ha! Picked up a straight crank and boom, clearance issues. Must be a bent frame in which the original crank was bent out to accommodate the clearance issue but the measurements on the chain stats match a good bike. So what gives?


Sent from my iPhone using Tapatalk
 
Install your peddles. If the crank arm/arms are bent you should be able to tell by the angle of the peddles. Is it the original chain guard? Maybe the chain guard is tweaked? Try moving the guard as far forward as possible. If that doesn't work, try going aft. Position it where the interference is the least. Then gently persuade the guard away from the arm.
 
What did you end up doing to resolve your issue?


Sent from my iPhone using Tapatalk
Sure did. I was able to correct it by doing the 2x4 trick. Somewhere there’s a thread on re-aligning the rear triangle. Mine was out of alignment on the drive side causing the crank arm to hit the frame. I’ll see if I can find the thread.
 
String test shows rear triangle to be evenly spaced in relation to the seat tube...if I did this correctly?
e257a2ed6db11d8dd35fb6807e9c95ae.jpg


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Sent from my iPhone using Tapatalk
 
Here are a few pictures of my 48 DX. As you can see there is not much clearance between the crank arm and the chainguard. How hard is your crank hitting your guard?
DSC_0586.JPG
DSC_0587.JPG
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DSC_0589.JPG
 
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