SS Build - Help Needed - PLEASE

[gb155]

Your not using a 3/32 chain with an 1/8 freewheel are you????

most freewheels are 1/8

had similar problem with a fixed sprocket that was supposed to be 3/32

On changing to an 1/8 th chain worked fine

Erm, would the chain give a size ?

 

[Pennine-Paul]

just measure the gap between the plates (on the narrowest links) should be 1/8

 

[gb155]

Yup it's 1/8

This is my chain line

 

[gaz]

Your chain line doesn't look straight, look just after your freewheel and you will see a kink in the chain line.
It looks like your wheel isn't straight, i would suggest putting the wheel in properly and getting some decent tension in the chain.

 

[fossyant]

That's miles off Gaz (Chain line). Where have you put the front chain ring - If it's on the outside of the spider, move it to the inside.

If you can't then how much space is there between the chain ring and frame. Because, you may need another BB with a shorter Axel.

Eg. if the BB has a 120mm axel, you may need 110 or less.

What hub is on there -is that a standard 130mm ?

Correct chain line:-

 

[gb155]

That's miles off Gaz (Chain line). Where have you put the front chain ring - If it's on the outside of the spider, move it to the inside.

If you can't then how much space is there between the chain ring and frame. Because, you may need another BB with a shorter Axel.

Eg. if the BB has a 120mm axel, you may need 110 or less.

What hub is on there -is that a standard 130mm ?

Correct chain line:-

This is how the front is set up

Can I put it to the outside ? ( would that even help ?

 

[Rohloff_Brompton_Rider]

won't do any good. you need to measure from the centre of the rear stays to the cog, and then from the centre of the bb to the same edge of the sprocket, they should be identical.

chainlines are easy with a single speed hub conversion kit (moving spacers around to get chainline correct, i.e, putting a kit onto a standard block carrier like shimano 8 speed for example) but with a ss specific hub, you need to buy a matching hub for the bb or vice versa.

it needs to be right or the chain will throw, usually at speed and may lock up the rear wheel, just when you don't want it to.



www.sheldonbrown.com


i think you may need to change the bb or use some spacers on the bb (too move chainline around).

 

[Rohloff_Brompton_Rider]

No from what we can see in the photos the chain leaves the cog and bends outwards so your chainring needs to be further in. As your chainring is on the inside of the spider this suggests a shorter bottom bracket is called for.

You do need a bit more chain to get the axle further back so it is more securely in the drop outs.

Have you looked at that link to see whether it is the right size?

he could put spacers on the non drive side of the bb, but i agree a shorter bb is the best option.

 

[gb155]

I have a sinking feeling im outta my league here and I thought SS would be a more simple build than a full geared carbon !

 

[Red Light]

Its not too difficult to get from where you are. Your chainline is definitely off but the fix is simple. Measure the rear cog position (measure the spacing between the insides of the drop outs and the distance from the inside of the drop out to the middle of the cog. The measure you need is half the first measurement minus the second to give you the distance from the mid line of the bike. Similarly measure the width of your bottom bracket and the distance from the edge of the bottom bracket to the middle of the chainring. The chainring distance is half the first measurement plus the second.

Now take the difference between those two measurements, subtract it from the current bottom bracket width and buy a new bottom bracket of the correct size. Worth doing a few checks on the current clearance between the cranks and the bottom bracket and cranks & chainring and chainstays to make sure the shorter bottom bracket will not cause problems there.

You may not be able to get exactly the right size BB in which case you may need to play around with spacers on the rear axle to move the hub and cog relative to the dropouts to fine tune it.

Good luck - it'll be worth it and you'll have a few more bike building skills in your kitbag when you're done. Most of us with fixed/SS have been through this ourselves.

 

[PpPete]

That video looks to me like a 3/16" chain on a 1/8" sprocket (which is a mistake I've made myself in the past).

Do not lose heart Gaz, getting chainline right on a fixed or SS conversion is always the biggest challenge - and we know you can deal with challenges.

On my fixed (which used an old 126 mm threaded hub) I got most of the way there by swopping spacers from one side of the axle to the other, and then re-dishing the wheel.

The problem with a shorter BB is that if you are not careful you end up with chainring (or even the crank) fouling the chainstay, so figure out what your current spindle is and what clearance you have to spare before you buy a new BB.

_____

EDIT - Cross posted with Redlight - who explains it better !

 

[Rohloff_Brompton_Rider]

I have a sinking feeling im outta my league here and I thought SS would be a more simple build than a full geared carbon !

it is once you get your head around chainlines. all you gotta think of is that the chain and sprocket are on a straight line.

the easiest way to check and see for yourself, get a long straight edge, like a straight piece of wood, put against the chainring, then put against the sprocket teeth, everything should be touching the piece of wood (i.e., the front and rear of the chainring and sprocket teeth).

yours won't at the mo, but at least it will give you a visual idea to get your head around.

i hope i explained that ok.

shaun

 

[gb155]

it is once you get your head around chainlines. all you gotta think of is that the chain and sprocket are on a straight line.

the easiest way to check and see for yourself, get a long straight edge, like a straight piece of wood, put against the chainring, then put against the sprocket teeth, everything should be touching the piece of wood (i.e., the front and rear of the chainring and sprocket teeth).

yours won't at the mo, but at least it will give you a visual idea to get your head around.

i hope i explained that ok.

shaun

Thank I'll use that tip to try and get my head around it tonigh

Gaz

 

[PpPete]

That video looks to me like a 3/16" chain on a 1/8" sprocket (which is a mistake I've made myself in the past).

Having looked again at the video it could be an old (very stretched) chain on a new sprocket ? Combined with the sub-optimal chainline that will throw chain off like that.

My experience of fixed conversions is that, on the workstand, if everything else is right even a poor chainline won't throw the chain off the sprocket like that, so I think there may be something else to it as well as the chainline.

 

[PpPete]

Thank I'll use that tip to try and get my head around it tonigh

Gaz

I completely mis-read that the first time.
Thinks - head, long lengths of wood, etc etc