Bottom Bracket Length

[thefensman]

Looking for some help regarding bottom bracket, i,m currently restoring/upgrading an 18-23 Raleigh Banana replica and due to an ongoing back problem i,m changing the original down tube shifters to sti. I,ve already bought a full sora group set off ebay that has an Octalink bottom bracket but after giving everything a dry run on frame before its resprayed i,ve noted that with the 109mm bb and my 8 speed rear wheel [groupset is full 8 speed] fitted the chain line appeared miles out.The set i have is as previously stated 8 speed with double front gear. After checking various sites i note that Octalink bbs [for road bikes] come in 3 sizes :109-118-126 i think. According to what i,ve read 109 is for double chainrings and118 is triple, so will a 118 bb fix my problem. Original Raleigh bb is i think 126 but i am sure if i fit this length shaft it will put chain line out in even further again. If its any help i,ve cold set the frame as per Sheldon Browns web site with lengths of 4x2 to 130mm and am pretty sure my frame is straight.Any advice will be massively appreciated. Thanks Richie. Thefensman.

 

[Dusty Bin]

Difficult to know what you mean by 'miles out' - a pic would help...

 

[RecordAceFromNew]

Looking for some help regarding bottom bracket, i,m currently restoring/upgrading an 18-23 Raleigh Banana replica and due to an ongoing back problem i,m changing the original down tube shifters to sti. I,ve already bought a full sora group set off ebay that has an Octalink bottom bracket but after giving everything a dry run on frame before its resprayed i,ve noted that with the 109mm bb and my 8 speed rear wheel [groupset is full 8 speed] fitted the chain line appeared miles out.The set i have is as previously stated 8 speed with double front gear. After checking various sites i note that Octalink bbs [for road bikes] come in 3 sizes :109-118-126 i think. According to what i,ve read 109 is for double chainrings and118 is triple, so will a 118 bb fix my problem. Original Raleigh bb is i think 126 but i am sure if i fit this length shaft it will put chain line out in even further again. If its any help i,ve cold set the frame as per Sheldon Browns web site with lengths of 4x2 to 130mm and am pretty sure my frame is straight.Any advice will be massively appreciated. Thanks Richie. Thefensman.

All you need to do is to look up what model your chainset is, the code is FCxxxx on the inside face of the crank arm. For 8 speed octalink sora double chance is it is FC3301 if so according to this you need a 68mm shell British thread 113mm ES30 octalink v2 bb. Just make sure you don't end up getting and fitting an octalink v1 bb (which I think your 109mm might well be) or it will damage (or have damaged) your chainset because the splines are different and the steel spindle will make (or would have made) mincemeat out of your alloy crank. See pic below from Sheldon.

 

[Sterba]

When you widened the rear drop outs are you sure you moved them out 2.5cm each side of the centre line? Your misalignment sounds as if you may have set the right hand drop out too far out.

 

[thefensman]

Thanks for your responses guys.To answer your questions, yes i,m pretty sure i set both dropouts correctly and when i said chain line was a "mile out" i may have used wrong choice of words. What actually happened was front rings appeared to be to close to frame though not close enough to cause any rubbing etc,so when chain was moved to smaller cogs on rear the chain line seemed overly out of line when on small chain ring but ok on large ring, if that makes sense.I estimated that at most, chain was out of line when on little to little by around 9-10 mm hence my suggesting i needed the next size shaft. I bought groupset as a complete kit from a guy who was upgrading so i have no reason to think that anything is not compatible.As someone pointed out bb is 68mm x109.5mm octalink , marked Shimano BB-5500,BC1.37X24,cranks are marked FC-3301,175MM long.Cant decide if bb is V1orV2 but cranks appear to fit it correctly.Hope this may shed a little more light on my problem. Cheers

 

[RecordAceFromNew]

As someone pointed out bb is 68mm x109.5mm octalink , marked Shimano BB-5500,BC1.37X24,cranks are marked FC-3301,175MM long.Cant decide if bb is V1orV2 but cranks appear to fit it correctly.Hope this may shed a little more light on my problem. Cheers

According to Sheldon's link I provided earlier BB5500 is indeed v1, while your chainset requires a v2. If it has been fitted and tightened the bb would have partially chewed up and weakened the splines on your chainset. It is not quite as bad as misfitting the other way round, where it would have completely destroyed the shallow splines on the chainset, but it is still not ideal. A common mistake, unfortunately.

 

[thefensman]

According to Sheldon's link I provided earlier BB5500 is indeed v1, while your chainset requires a v2. If it has been fitted and tightened the bb would have partially chewed up and weakened the splines on your chainset. It is not quite as bad as misfitting the other way round, where it would have completely destroyed the shallow splines on the chainset, but it is still not ideal. A common mistake, unfortunately.

Thanks RecordAce,but are you telling me that i need a new bb and chainset now. This build is turning into a money pit i fear

 

[thefensman]

Just been having a look through my parts box and have found a 9 speed square taper dual chainset, may buy a new UN54/55 BB and fit them if it would work? Would someone be able to post pics of what crank sockets look like so that i can tell if or how badly damaged mine may be. I have no previous knowledge of octalink as only used square taper in the past.

 

[PpPete]

Just been having a look through my parts box and have found a 9 speed square taper dual chainset, may buy a new UN54/55 BB and fit them if it would work?

It should do. Won't hurt to try. But if the chainset is ISO taper you might still have chainline problems.
UN54/55 are the (much more common) JIS taper.

 

[RecordAceFromNew]

Just been having a look through my parts box and have found a 9 speed square taper dual chainset, may buy a new UN54/55 BB and fit them if it would work? Would someone be able to post pics of what crank sockets look like so that i can tell if or how badly damaged mine may be. I have no previous knowledge of octalink as only used square taper in the past.

All else being equal I would certainly pick a square tapered over an octalink - octalink bb's are handicapped at birth by having teeny tiny ball bearings because the "industry" woke up one morning and decided that they could cut weight by 50 grams if they made the spindle larger and hollow, which gave rise to the octalinks and isis. Actually that experiment with users' money is still ongoing with the variety of outboard and pressfit bb's today, which typically are prone to misalignment and therefore disastrous user experience in terms of bb reliability. The added joke is that increased rigidity of bb spindle is also often given as a reason for such "progress". There is no prize for guessing who benefited with each evolution of incompatible chainset/bb.

I see no reason why your 9 speed square tapered double chainset with a suitable bb won't work perfectly. It might actually work out cheaper because the supply of octalink bb's is becoming scarce. If you don't know which bb to get to deliver the correct chainline the chainset's make and model code might help.