Looking for a crank arm that is 118mm for single chainring setup

[XE007]

I am a bit frustrated and I think I give up looking. I am wasting countless hours
searching for parts (crank arms) that are compatible for a bike utilizing
a 68mm-118mm without making huge sacrifices. I have a Schwinn Loop that I am trying to upgrade/downgrade
into a single speed setup utilizing the current wheelset with a cassette hub.

I was advised on another forum to just grab the a 110mm BB and use whatever crank arm is designed for
to work with those crank arms. I wanted a nice pair of Andel crank arms but it seems that most track
crank arms utilize at least a 110mm to my dismay.

I would love to do this but the problem is that if I go 110mm my chainline will get smaller and then
my chain which is just at the 1st cog will misalign.

Any suggestion?

 

[rogerzilla]

Is your chainline straight at the moment? You can only check it properly with a 2' steel rule or similar straight edge. Don't bother measuring it af the chainring and sprocket, as few frames are millimetre-straight.

If so, tell us exactly what crank and BB you're running at the moment, including the taper.

 

[fossyant]

110mm is the standard for a fixed/singlespeed track chainset, but you can go with a longer axel for a geared set up.

 

[rogerzilla]

110mm is the standard for a fixed/singlespeed track chainset, but you can go with a longer axel for a geared set up.

There is no standard - 110mm works for some old-style straight cranks.

There's not even a real standard for track chainline. Campag stuff is 42.5mm, I think Dura-Ace is 42mm, but TA is about 46mm. If you're using road-derived cranks, 46mm is usually where you end up even with a 103mm BB.

 

[Ajax Bay]

Title: "Looking for a crank arm that is 118mm for single chainring setup"
Don't think you mean this. Those would be real short cranks and made of unobtainium.
The length of the bottom bracket COMBINED with a chainset determines the chain line.
Work out the chain line for your frame/wheel/single sprocket by measurement (?~44mm) of the rear hub (centre to middle sprocket). Consider if you have any flexibility in positioning the sprocket on (as I understand) a 'normal cassette' freehub.
Put your desired Andel crank on (on the 118mm BB) and see what chain line that gives you - if it is designed for 110mm, then putting on a 118mm BB (existing?) will place the chainring 4mm further out. Then if necessary replace the BB with a UN-55 of spindle length to get the chain line right.
Bear in mind that the spacing between adjacent sprockets on a cassette is 5+mm so having the chainline out by 4mm at the front is not, mechanically, an issue: it'd be the same as using a sprocket adjacent to the single one you plan to run (on the ?8-10sp freehub).

 

[rogerzilla]

Also bear in mind that many cranks will bottom out on the cups of a short BB, like a 103mm (made by Tange, Token etc). The limit for Andel track cranks is 107mm. Some cranks have a chamfer to allow them to slip inside the cup a little.

 

[XE007]

Also bear in mind that many cranks will bottom out on the cups of a short BB, like a 103mm (made by Tange, Token etc). The limit for Andel track cranks is 107mm. Some cranks have a chamfer to allow them to slip inside the cup a little.

Thanks for your reply. The Andel cranks available need a 110mm BB.

 

[XE007]

Title: "Looking for a crank arm that is 118mm for single chainring setup"
Don't think you mean this. Those would be real short cranks and made of unobtainium.
The length of the bottom bracket COMBINED with a chainset determines the chain line.
Work out the chain line for your frame/wheel/single sprocket by measurement (?~44mm). Consider if you have any flexibility in positioning the sprocket on (as I understand) a 'normal cassette' freehub.
Put your desired Andel crank on (on the 118mm BB) and see what chain line that gives you - if it is designed for 110mm, then putting on a 118mm BB (existing?) will place the chainring 4mm further out. Then if necessary replace the BB with a UN-55 of spindle length to get the chain line right.
Bear in mind that the spacing between adjacent sprockets on a cassette is 5+mm so having the chainline out by 4mm at the front is not, mechanically, an issue: it'd be the same as using a sprocket adjacent to the single one you plan to run (on the ?8-10sp freehub).

Thanks. I went ahead and measured the chainline by pushing in the chainring enough to give me 42mm which is what is required for these crank arms. I do not have the crank arms yet as I am afraid that they might not be compatible but I took picture last night to make sure that the chain runs across straight so i have some hope. The only problem is that by pushing in the chainring now means that my chainring size is limited but i am okay with that.

 

[XE007]

Here are new images with some details as I just ordered the UN55 68x110mm

With my daughters help, we put the chainring against the BB insert (I have no BB installed yet but using the old broken one to hold the two crank arms) and took a picture of an overview and the chain is on the sixth gear. I will add that the Schwinn loop has a cheap chainring welded unto the drive crank arm.

Here is the second image of the chainline measurement:

Again, with the chainring against the BB insert I can see that it is a few mm off which I think that once the UN55 is installed, the new BB should sit out further more from its housing and I think should sit at the fifth gear? I think that should put the chainline around the 5th gear (bike is 7 speed)?

Thank you for any clarification and thanks for your patience as this is school for me as I am a newb but I feel like I need to learn this hands on.

 

[rogerzilla]

I think you're tying yourself up in knots here. With a 7 speed (I thought it was a singlespeed from the original post) and a single ring, you ideally want the chainring to line up with the middle sprocket, i.e. the fourth one. If it is Shimano then this is a chainline of 43.5mm for a road frame. So just use the Andel cranks, which are supposed* to give a 42mm chainline with a 110mm BB, with a 113mm bottom bracket (113 = 110 + (1.5 x 2)) assuming the BB is symmetrical.

Caveat: few frames are straight so it is better to measure how far out you are and correct for that. You need twice the difference in BB length for the change in chainline.

*They are not the highest quality and some slide further onto the taper than others. I have three pairs here and none give the factory specified chainline.

 

[midlife]

Is that bottom bracket in the right way? seems like the non-drive side crank is sticking out a mile while the drive side crank is almost touching the BB..

 

[Ajax Bay]

Think BB used for images is "broken one".

 

[XE007]

Think BB used for images is "broken one".

Yes.

 

[XE007]

Is that bottom bracket in the right way? seems like the non-drive side crank is sticking out a mile while the drive side crank is almost touching the BB..

It is broken. I am just illustrating an example. i should have been more clear.

 

[XE007]

I think you're tying yourself up in knots here. With a 7 speed (I thought it was a singlespeed from the original post) and a single ring, you ideally want the chainring to line up with the middle sprocket, i.e. the fourth one. If it is Shimano then this is a chainline of 43.5mm for a road frame. So just use the Andel cranks, which are supposed* to give a 42mm chainline with a 110mm BB, with a 113mm bottom bracket (113 = 110 + (1.5 x 2)) assuming the BB is symmetrical.

Caveat: few frames are straight so it is better to measure how far out you are and correct for that. You need twice the difference in BB length for the change in chainline.

*They are not the highest quality and some slide further onto the taper than others. I have three pairs here and none give the factory specified chainline.

Sorry for the confusion. Yes, it is a 7 speed but for the first year because of the terrain I am on, I want to make this a single speed. I stumbled across a sheldon website and according to him setting up a single speed on a cassette is easier. By the way, thank you for the reply and assistance but please bear with me as I am not math savvy.

So the bicycle had originally a 118mm BB. So you are saying to go 113mm and that should help? Or will I need some sort of spacer as well? Forgive me for asking, what about the BB needs to be symmetrical? It is a square taper Shimano.

They are not the highest quality

You mean the Andels?

Thanks again Rogerzilla.