's Forum Archives - Fixed Gear

Archive Home >> Fixed Gear

Chainline problems are killing me - any suggestions?(7 posts)

Chainline problems are killing me - any suggestions?Steve Young
Jan 13, 2004 4:57 PM
O.K. Here's the story. I started with a very nice perfectly functional Fuji Track 2003. You'd have thought I would have been happy with that but oh no - I had to go and mess with it.

I have now changed out the wheels for Open Pro's on Phil Hubs and swapped out the chainset for a Campy Pista which is now mounted on a Phil BB giving me flexibility to move the chainline up front +/- 5mm

I measure the chainline at the back as follows:
The distance between the dropout and the centre of the cog at the rear is 18mm
The rear dropout spacing is 120mm and the overlocknut dimension on the (Phil Track) hub is also 120mm.
Thus I figure chainline should be (120/2)-18=42mm

I measure the chainline of the front as follows:
The distance between the middle of the chainring teeth and the seat tube is a shade under 28mm (say 27.6mm) and I can adjust a bit more closely.
The diameter of the seat tube is 29mm so half this (14.5) plus the distance to the chainring (27.6) gives a chainline of 42.1mm
My understanding is that chainline is the distance between the midline of the cog/chainring teeth and the centreline of the bike.
Thus is they are both 42mm shouldn't the chainline be perfect ?
Apparently not, because even with this set-up the chain is noisy and actually skips if I back pedal (Bike still on the workstand at this point).
It looks as if the inner sideplates of the chain are hitting (as opposed to meshing with the outside of BOTH the chainring and the cog).
I've measured the chainline loads of times on different days with digital calipers (and also with a steel ruler). I always get the same measurement (in the former case to within 0.1 of a mm).
What am I missing here - the only thing I haven't replaced is the chain but with only 500 miles on it should be fresh shouldn't it? The only possible cause of a problem is that when I sight along it rom the back of the bike it does appear to curve laterally slightly. However I can't believe I have damaged it as it was fine before I started on this upgrading exercise and has never been subject to any abuse (I've never thrown it). Only possible suggestion is that I did ride 20 miles on it with a less than perfect chainline when testing first out.

The wheel is perfectly aligned in the dropouts (I measured the spacing with a digital calliper and it's within 1mm at all points around the rim/stay spacing - that's the limit of the truelness of the wheel I think).

Tonight I am going to check the wheel alignment one more time and then tear it all apart and put it back together as original (I need to ride it!!!) and if the problem is still there I will replace the chain.

Does anyone PLEASE have any suggestions - I'm getting a bit desparate here.

I know I could take it to the LBS - I'm sure they would sort it our really quickly but I want to work this out myself.

Thanks for reading all this !

re: Chainline problems are killing me - any suggestions?ukiahb
Jan 13, 2004 6:10 PM
something wierd is happening there...that is the right way to measure chainline, and I doubt riding with the chainline off for awhile is causing your problems. It might be a good idea to do a quick check your frame alignment (since the chain appers to curve), could do this by stretching a string from the center of the seat tube to the center of a rod or old hub bolted in the dropouts and sighting to see if it is line with the main frame tubes. If you put a long rod through the dropouts and sight from the front it will will be easy to see if the frame is twisted. I'd try a different chain too since they are cheap and you'll need one eventually anyway....
ouch, I'd also say the frame checkclimbo
Jan 14, 2004 7:10 AM
would be the next thing, maybe it is twisted just enough. I can't imagine your hub is the problem, it's a new Phil hub so it should be perfect.

That or you may need a witch doctor to clear out the bad voodoo ?
Thanks - I just oredered a new chain so we'll see (nm)Steve Young
Jan 14, 2004 7:59 AM
It's simple to tell using a direct method...rcmann
Jan 14, 2004 8:47 AM
...if your chainline is aligned-just lay the edge of a straightedge (like a metal carpenter's square) along the chainring and the cog. Do this under the chainstay with the chain off and make sure the straightedge isn't laying on any chainring bolts. If the edge is laying dead flat on both cog/ring the chainline is perfect. If not, move the BB spindle in/out (since you have a Phil it's easy) until they're aligned. This completely removes all measuring error because you're not measuring. It does, however, assume your cog and chainrings/cranks aren't warped or something.
The hub may not be aligned in the dropouts...TFerguson
Jan 14, 2004 10:32 AM
If I get your measurement of wheel alignment, you just measured the trueness of the wheel itself. If the hub itself is not aligned, the cog will be out of line. Get a measurement from center of BB to center of axle on both sides. (Thinking about it, maybe you did check the wheel/hub alignment, but this will still give you some more information.)

Also, with the chain off, sight along the cog to the chainring. You can quite easily see if they are not pointed at each other.

I checked the chainline on my steel Bianchi (which has seen abuse and cold setting) by your method, by sighting, and by using the Park alignment tool. Got three different answers. I reasoned that (unless I want to actually take it to a frame jig for alignment) the sighting method is the best since the objective really is to prevent the chain from being at an angle to the cog or ring.

Is the bottom bracket shell centered w/r/t the seattube?Roundabout
Jan 14, 2004 2:52 PM
Measure the width of the bottom bracket shell and then add one half of that to the distance from the drive side of the bottom bracket shell to the centerline of the chainring. See what you come up with and compare that to the 42 mm rear cog chainline.