What is going on here?


This ad disappears when logged in

ballooney

Wore out three sets of tires already!
Dec 5, 2010
520
1,048
Santa Rosa, United States
#1
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
 

Dan Shabel

Finally riding a big boys bike
Jun 17, 2017
139
240
St. Louis
#5
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.
 

rollfaster

Riding a '38 Autocycle Deluxe
Dec 28, 2012
7,522
6,404
52
Ol' st. Lou
#6
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.
 
Likes: pdmccool

ballooney

Wore out three sets of tires already!
Dec 5, 2010
520
1,048
Santa Rosa, United States
#7
String test shows rear triangle to be evenly spaced in relation to the seat tube...if I did this correctly?
e257a2ed6db11d8dd35fb6807e9c95ae.jpg


40e08c42853d3808988ee8047595f569.jpg


bdf05f3a651d66b18ead2cee80e9ca77.jpg




Sent from my iPhone using Tapatalk
 

Dan Shabel

Finally riding a big boys bike
Jun 17, 2017
139
240
St. Louis
#8
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
DSC_0588.JPG
DSC_0589.JPG
 
Likes: WetDogGraphix

ballooney

Wore out three sets of tires already!
Dec 5, 2010
520
1,048
Santa Rosa, United States
#10
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?
The crank is completely blocked by the guard.
 

buickmike

Wore out three sets of tires already!
May 26, 2014
926
670
Indianapolis, United States
#11
i.d. like to add . The chainguard can be mounted in inside of frametab or outside. Depending on clearance requirements.. I thought I saw maybe fender didn't have relief for chainguard to tuck in. Been a long time since I built this 48. Barely clearing on non drive side. The bearing cone - all diff size so I had to choose a good 1 And cups were worn etc. I hope you have plenty of spare parts for this build.

uploadfromtaptalk1513547506646.jpg


uploadfromtaptalk1513547529606.jpg


uploadfromtaptalk1513547743529.jpg
 

ballooney

Wore out three sets of tires already!
Dec 5, 2010
520
1,048
Santa Rosa, United States
#16
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.
Thanks for your input. The chain guard is original. I have mounted the guard on the inside of mounting tab and outside...no luck with clearance.
 

ballooney

Wore out three sets of tires already!
Dec 5, 2010
520
1,048
Santa Rosa, United States
#17
i.d. like to add . The chainguard can be mounted in inside of frametab or outside. Depending on clearance requirements.. I thought I saw maybe fender didn't have relief for chainguard to tuck in. Been a long time since I built this 48. Barely clearing on non drive side. The bearing cone - all diff size so I had to choose a good 1 And cups were worn etc. I hope you have plenty of spare parts for this build.

View attachment 726079

View attachment 726080

View attachment 726081
I have just the opposite for clearances...plenty of clearance on the non-drive side but barely clears on the drive side. Yet, with the string test, the rear triangle appears true. Strange.
 

ballooney

Wore out three sets of tires already!
Dec 5, 2010
520
1,048
Santa Rosa, United States
#18
Theres a jig to check the trueness of the frame
I used a string from rear-drop outs, around head tube and back around. Measuring seat tube to string appears to be the same for both sides concluding the rear triangle is in alignment. Could the bottom bracket be off? Puzzling!
 

buickmike

Wore out three sets of tires already!
May 26, 2014
926
670
Indianapolis, United States
#19
Just looked at pic showing "straight. crank in frame. .Definitely too many threads exposed on non sprocket side. So lets move it (crank) over with intent of clearing frame. When I work on bikes lately I'm limited to parts that are usable. Schwinn stuff is common but older parts from 10 spd. would work? What I would look for are adj. Cones of diff. Thicknesses. All I have left now are repro anniversary BB cups. threw all worn out cups+cones away. Looking at BB on mine you see thicker cups.
 

ballooney

Wore out three sets of tires already!
Dec 5, 2010
520
1,048
Santa Rosa, United States
#20
Just looked at pic showing "straight. crank in frame. .Definitely too many threads exposed on non sprocket side. So lets move it (crank) over with intent of clearing frame. When I work on bikes lately I'm limited to parts that are usable. Schwinn stuff is common but older parts from 10 spd. would work? What I would look for are adj. Cones of diff. Thicknesses. All I have left now are repro anniversary BB cups. threw all worn out cups+cones away. Looking at BB on mine you see thicker cups.
Great suggestions. I’ll check the cups and compare with another B6 and try to work the crank threads over giving more clearance on the drive side. I will also expirement with mounting the guard on different sides of the mounting bracket one more time.
 

This ad disappears when logged in
Most Recent BUY IT NOW Items Listed on eBay
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture
eBay Auction Picture