th0m

Hopefully someone can help me out with this. I've mounted a brand new Phil Wood square taper BB with the ITA cartridge cups on a Colnago Master I'm restoring. Because of the way the BB and the cups are constructed, you are basically able to position the thing any way you want inside the shell, thereby changing the chain line.

This might be a stupid question, but I've never worked with this type of BB before and need some advice; what part of the frame should I use as "reference" when positioning the bottom bracket to achieve the correct chain line? I have now simply measured the distance between the ends of the square taper axle and the shell, but when I mounted the crank arms, they are of equal distance from the down tube, but not from the seat tube or the chain stays, where the difference is about 2,5-3 mm from side to side. Should I align the BB by using the shell and down tube, or by using the seat tube and chain stays?

Would really appreciate any help you could give me

Unca_Sam

You sound confused, and you confused me.

Your chain line is something that your rear hub and cassette or freewheel defines, with a range of possibilities that are acceptable for a frame and BB/crankset combo.

What is the OLN for the rear hub are you using? How many cogs? The chain line you want to aim for is the distance from the OLN center to the center of the rear cluster. Install the DS crank arm on the BB axle tightly, then measure from the centerline of the seat tube to the space between the two rings on a double, or at the center ring on a triple to find the chain line there.

It's MUCH more important on a single speed or FG bike, to keep noise and wear down, but a derailleur equipped bike has more leeway between the measurements. I don't have that number, but up to 2mm is acceptable for SS or FG applications, depending on the chainstay length.

Unca_Sam

Using 'chainline derailleur' in google delivered Park Tool's guide first, and Sheldon Brown's second. Either one will give you a better primer than I did.

3alarmer 

...first, I absolutely do not understand what this says, or how it is possible for the down tube and the seat tube to be differently spaced from what should be the same reference point in the BB shell.

But to get to the point, I have never used the frame itself as a reference in establishing the ideal chainline. There might be a way to do this, but I don't know it. When I do this, I dry fit everything, including the BB unit installed (but not Loctited in place), the rear wheel (with cog cluster or freewheel mounted on it), the drive side crankarm (with chain wheels mounted), and the chain cut to length and fitted through the rear derailleur and the front one. You also will find it easier if the shifters are installed and cabled. Basically a functioning drive train, but you don't need the front wheel or the non drive side arm installed.

The ideal chainline is whatever position for the BB unit that aligns the imaginary line from the space between the two front chain rings (or the middle ring, if you have a triple crank), with the centermost spot on your rear cog cluster. This might be a cog, or it might also be a space. I usually don't measure this, I just use a steel tape or straightedge (or a yardstick, etc.) and look at the line that it makes eyeballed from the front, and eyeballed from the back. Eyeball when looking square at the frame from about the rear wheel perspective, then moving out to about the center of the cog cluster, is usually enough to give you a pretty good idea of what's going on.

Once the spindle is in the best position, try shifting the chain through all the gears, and see what kind of angles you are getting as the chain goes farther off center, going up and down the cluster.

When you are happy with it, remove the chain, and mark somehow the position of the unit with a line on the spindle right where it is even with the BB shell outside edge.

You keep the drive side crank arm loose, so that you can pull it off to readjust the retaining ring on that side. The non drive side arm is already off. You need to use Loctite for the final installation (unless they've changed these instructions, or are now using some kind of locking compound on the retaining rings they now sell at Phil Wood.) It is true that installing the drive side arm at full torque will move it in a little bit, so you might want to allow for that, by moving the BB unit a skosh in the outward direction toward the drive arm, to compensate. It's not usually enough to worry about.

All of this sounds more complicated than it turns out to be in practice. But it's all I've ever done. these Phil Wood BB units are directional, so make sure you don't get it reversed. Something bad can happen to the bearings and internal adjustment in use if you install it backwards.

Bill Kapaun

Set it so the chain runs the straightest in the majority of the cogs you use the most.
My bikes are 3X9 where I predominately use the middle ring & outer cogs.
In that case, I set the chain line out a couple extra mm.

You don't have a lot of leeway, since the FDER still has to work properly within its range.

th0m

Thanks for your comments, very helpful. My thinking was that as long as you've positioned the BB perfectly symmetrical within the shell, the chain line would automatically be fine. Seems like that's not necessarily the case though, especially since there's obviously some variations in the frame itself. Guess I'll have to do it by sight instead then as soon as I've mounted the rest of the drive train.

Again, many thanks.

trailangel

I don't know what an ITA bottom bracket is. ... but hopefully you have mounted the BB so Phil Wood logo reads correctly looking forward.

th0m

Italian threaded. ITA is the common abbreviation as far as I know. It's mounted the right way, I assure you. Read the instructions a number of times

Mr. 66

I'm wondering, with your details of measurement, is your frame in alignment?

th0m

It's never been crashed and is in great condition overall with original paintwork, so any variations should be from manufacturing, intended or not.

Still waiting for delivery of the new wheel set, so hopefully things will be more obvious once everything is mounted.

70sSanO

I've never used a Phil Wood BB, but I've similar used ones that had lock rings to hold the cartridge bearing cups.

Once you get your new wheel, you can check to see you have a good chainline by lining up the chain to the freehub body. The crankarm distance from the chainstays does not need to be the same on both sides, but obviously it has to clear, as well as the chainrings.

If you need to remove the crank and make adjustments, you might want to consider if you want the chainline centered, or shaded in one direction or the other. I set up one of my mountain bikes to have a slightly inward tweak to the chainline. I did it so that I could run more cogs with less of a cross-chaining on the large chainring (it was a double). There are times when I would want to run a large-large, but rarely, if ever, a small-small. I'm not suggesting that you do this, but since the chainline on that BB is adjustable to some extent, it is possible.

John

JohnDThompson 

BITD, you'd take the Campagnolo straightedge "G tool," drop one end between the two chaingrings and have the other end rest on the middle sprocket of the rear cluster. If it landed elsewhere on the cluster, you put spacers behind the fixed cup or freewheel to get it to line up properly.