Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

b-screw ineffective on Sora RD-3300

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

b-screw ineffective on Sora RD-3300

Old 12-26-07, 12:00 PM
  #1  
Junior Member
Thread Starter
 
Join Date: Dec 2007
Location: UK
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
b-screw ineffective on Sora RD-3300

I hope someone can help me with this problem. A wheel change necessitated a new cassette because my old one refused to come off (cassette lock sheared off! - it was old). The old cassette was 6 gears and the new one is 8 gears Shimano.

Since only 6 gears were being indexed I put new shifters and a rear derailleur on my christmas list. I put them on yesterday but have run into a problem with the rear derailleur (Shimano Sora RD-3300 8 speed).

The pulley is rubbing against the cog. I've adjusted the b-screw from one extreme to the other but it has made no difference whatsoever. It is positioned correctly (against that bit on the frame - sorry I don't know the technical word for it). I've tried shifting up and down as well as observing as I adjust and there's absolutely no difference.

Temporarily I've 'solved' the problem by pulling the cable housing that goes into the derailleur up over a bolt that holds the mud guards in place. This has the effect of moving the derailleur so that the pulley positions a bit further away and no longer rubs. However, this is obviously a bit of a bodge.

This is the first derailleur I've installed so I assume I've done something wrong. Could chain length be an issue?

Thanks for any help you can give,
Joe
JoeWright is offline  
Old 12-26-07, 12:29 PM
  #2  
Senior Member
 
Sci-Fi's Avatar
 
Join Date: Sep 2006
Posts: 1,329
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 16 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Chain sounds like it's too short.

Chain length sizing:
https://www.parktool.com/repair/readhowto.asp?id=26

Then the "B" screw will work for proper adjustment/clearance on the largest cog:
https://www.parktool.com/repair/readhowto.asp?id=64
Sci-Fi is offline  
Old 12-26-07, 02:16 PM
  #3  
Junior Member
Thread Starter
 
Join Date: Dec 2007
Location: UK
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Thanks for the chain length link.

I have the values C=17.5", F=48, R=26, L=54.5" (or 54.6748 if using complex formular).

I've measured the chain I've got at 56.6". It's quite old and I think its stretched a bit - hence the 0.6"

So if anything my chain is too long. Does this make sense?


Thanks, Joe
JoeWright is offline  
Old 12-26-07, 03:41 PM
  #4  
Senior Member
 
royalflash's Avatar
 
Join Date: Mar 2004
Location: Munich
Posts: 1,372

Bikes: Lemond Alpe d´Huez, Scott Sub 10, homemade mtb, Radlbauer adler (old city bike), Dahon impulse (folder with 20 inch wheels), haibike eq xduro

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
It is not very helpful but the B-screw can be a bit like that- you adjust it and not much seems to happen-it is not a good idea though to leave the pulley rubbing against the cog as I found from painful experience that it can cause your chain to be torn apart if you try and shift under extreme load at the wrong time and also it will eventually damage the derailleur.

Is the biggest ring of the new cassette bigger than the old one - could it be that the new cassette is too big for the derailleur-not every cassette works with every derailleur.
__________________
only the dead have seen the end of mass motorized stupidity

Plato

(well if he was alive today he would have written it)
royalflash is offline  
Old 12-26-07, 05:54 PM
  #5  
Junior Member
Thread Starter
 
Join Date: Dec 2007
Location: UK
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
The cassette is also new - HG50 8 speed (if I remember correctly). Its the right cassette/derailleur combo according to Shimano. The old components are the chain and the whole crankset.

Cheers, Joe
JoeWright is offline  
Old 12-26-07, 09:35 PM
  #6  
Cat 6
 
Ex Pres's Avatar
 
Join Date: Dec 2007
Location: Mountain Brook, AL
Posts: 7,519
Mentioned: 27 Post(s)
Tagged: 0 Thread(s)
Quoted: 500 Post(s)
Liked 183 Times in 118 Posts
You can move the wheel forward in the dropout (assuming horizontal) to help alleviate this a little, too.

Chain length might be an issue as noted. Instead of all that fancy figurin', use Sheldon's method
__________________
72 Frejus (for sale), Holdsworth Record (for sale), special CNC & Gitane Interclub / 74 Italvega NR (for sale) / c80 French / 82 Raleigh Intl MkII f&f (for sale)/ 83 Trek 620 (for sale)/ 84 Bruce Gordon Chinook (for sale)/ 85 Ron Cooper / 87 Centurion IM MV (for sale) / 03 Casati Dardo / 08 BF IRO / 09 Dogma FPX / 09 Giant TCX0 / 10 Vassago Fisticuff








Ex Pres is offline  
Old 12-26-07, 09:58 PM
  #7  
use your best eye
 
kenhill3's Avatar
 
Join Date: Mar 2006
Location: Olympia, Washington
Posts: 3,050

Bikes: '75 Bertin, '93 Parkpre Team 925, '04 Kona King Kikapu, '05 Bianchi Vigorelli

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 1 Time in 1 Post
+1 0n Sheldon's method, which is also the method Shimano specifies.
__________________
"I tell you, We are here on earth to fart around, and don't let anybody tell you any different." - Kurt Vonnegut jr.
kenhill3 is offline  
Old 12-27-07, 06:25 AM
  #8  
Junior Member
Thread Starter
 
Join Date: Dec 2007
Location: UK
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Thanks for the feedback everyone. However, now I'm more confused than ever.

I spotted a diagram for recommended chain length in the instructions for the rear derailleur. In that they have the chain feeding through both derailleurs and around the largest sprocket at the front and the smallest at the rear. The diagram suggests the bottom side of the chain should slant slightly down towards the crank but mine is either horizontal or slightly upwards. This to me would suggest the chain is too short like everyone is saying.

However, I've done the Sheldon method (also re-iterated on the Park Tool site) and by that method my chain is far too long. It hangs very loose. The only thing is, if it isn't fed through the rear derailleur then surely its going to hang very loose as it doesn't have to feed round the two extra cogs?

Am I misunderstanding the Sheldon method or is my chain really way too long?

Thanks, Joe


Last edited by JoeWright; 12-27-07 at 06:39 AM.
JoeWright is offline  
Old 12-27-07, 08:24 AM
  #9  
Senior Member
 
royalflash's Avatar
 
Join Date: Mar 2004
Location: Munich
Posts: 1,372

Bikes: Lemond Alpe d´Huez, Scott Sub 10, homemade mtb, Radlbauer adler (old city bike), Dahon impulse (folder with 20 inch wheels), haibike eq xduro

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
bearing in mind I am just a wally on the internet and not a qualified bike mechanic- my understanding of the chain length thing is that the chain should be long enough so that you can shift to the largest sprocket at the front and the largest at the back (not that this a recommended combination) with a little bit of extra chain length spare but this should be a minimum. The big/big combination is what ultimately determines the chain length. If you shift to this combination and the chain is not long enough then the drive train will sieze up with possibly disastrous consequences. Thus, when you shift to other smaller sprockets (front or back) and the chain doesn´t need to be as long, the derailleur takes up the slack with its spring action and effectivley shortens the chain. You shouldn´t have too much slack or the derailluer won´t be able to take up the slack. So you can basically see how much chain you need just by wrapping the chain round the big/big sprockets (edit: i meant while the chain is routed normally through the derailleur of course) and adding a little bit.
__________________
only the dead have seen the end of mass motorized stupidity

Plato

(well if he was alive today he would have written it)

Last edited by royalflash; 12-27-07 at 11:18 AM.
royalflash is offline  
Old 12-27-07, 08:39 AM
  #10  
Senior Member
 
Join Date: Apr 2007
Location: Central Florida
Posts: 59

Bikes: Raleigh Passage 3.5

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I can't really tell in the picture, but is the chain routed through the derailler correctly? For the chain to that much difference in length from the old set up, there would have to be a major change in the size of the cassette.

John
Rumblejohn is offline  
Old 12-27-07, 09:17 AM
  #11  
use your best eye
 
kenhill3's Avatar
 
Join Date: Mar 2006
Location: Olympia, Washington
Posts: 3,050

Bikes: '75 Bertin, '93 Parkpre Team 925, '04 Kona King Kikapu, '05 Bianchi Vigorelli

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Joe-

In your picture it appears that your chain is NOT routed through the rear derailleur, that is proper for the Sheldon/Shimano method to determine chain length. Also, the chain looks to be going around the biggest rear cog and the biggest front chainring- that is also correct for this method. Now, figure out how long the chain would need to be to be to be TIGHT in this position, then add 1 inch (two links/two pins) to the length. Break the chain there, thread the chain properly through the rear derailleur and the front derailleur cage and join the chain. Make sure that the place where you cut (break) the chain for length is the right inner or outer set of side plates to connect properly to the other end of the chain- if it is not, just add 1/2 inch (one link/one pin) to get the right combo.

Go back to Sheldon and Park to double check.

Hope this helps.
__________________
"I tell you, We are here on earth to fart around, and don't let anybody tell you any different." - Kurt Vonnegut jr.
kenhill3 is offline  
Old 12-27-07, 11:20 AM
  #12  
Senior Member
 
royalflash's Avatar
 
Join Date: Mar 2004
Location: Munich
Posts: 1,372

Bikes: Lemond Alpe d´Huez, Scott Sub 10, homemade mtb, Radlbauer adler (old city bike), Dahon impulse (folder with 20 inch wheels), haibike eq xduro

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by Bob Barker
I concur with ken that you're doing it right so far, just finish it up, and I also agree with you that it appears that this means your current chain is too long.

I hope you will buy a new chain for this for 2 reasons:
1. Your chain has stretched and will not shift well with a new cassette, plus
2. You may have had a 6s Uniglide cassette, and you now have an 8s Hyperglide. The Uniglide teeth were wider and had their own Uniglide chain to work with these.
plus a stretched chain will wear out your new cassette and your chainwheels more quickly
__________________
only the dead have seen the end of mass motorized stupidity

Plato

(well if he was alive today he would have written it)
royalflash is offline  
Old 12-29-07, 05:12 AM
  #13  
Junior Member
Thread Starter
 
Join Date: Dec 2007
Location: UK
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Very strange thing: I reconnected the derailleur and it was happy! No more rubbing - good position. Its now running pretty smoothly.

The only thing I can think of is that in partially dismantling the derailleur to get it round the chain I mucked something up first time round. Anyone - the original problem is solved (although I haven't tried the b-screw but since its happy I'm not going to touch it).

Thanks for the chain recommendation - that's my next upgrade.

Thanks to everyone for your help, Joe
JoeWright is offline  
Old 12-29-07, 08:15 AM
  #14  
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 33,656

Bikes: '96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '20 Surly Midnight Special, All are 3x10. It is hilly around here!

Mentioned: 39 Post(s)
Tagged: 0 Thread(s)
Quoted: 2026 Post(s)
Likes: 0
Liked 1,095 Times in 741 Posts
Originally Posted by SST
Going from a 6 speed cassette to an 8 will make your old chain to short.
Why? Please explain. If the overall tooth range, particularly the largest cog, is the same why would the number of cogs make any difference?
HillRider is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.