Chainline...the (Mc)bane of my life

Alright, so when I was building my McBain, I had a few issues with the chainline. The main problem was the drive side crank ran super close to the chainstay (query here), anyway I thought I had that licked with an ISO/ISO spindle/bottom bracket combo.

Now that it’s up and running, the drivetrain is really noisy. I couldn’t figure out why, then with a closer inspection I noticed the chain wasn’t engaging with the sprocket very well. So I took the chain off and I could see the sprocket and chainring were not aligned.

So I clamped a steel rod to the face of the chainring to see how far out the sprocket was. The result - 9mm…whaaaat?! See below:

So how did this get so far out? Admittedly most of my calculations were quite theoretical prior to getting the desired parts, but 9mm? It was meant to be 1.5!

So there are three areas that may have contributed to the problem.

  1. There are three spacers on the non drive side of the hub - 2mm/1.5mm/2mm (see pic below). Is this a normal installation for a track hub? It made sense to me as it made up the 120mm dropout spacing, as well as taking up the space that the sprocket took on the drive side, allowing for a minimally dished wheel. I could put the spacers on the drive side, but I’d only be 5.5mm better off, and my wheel would need to be re-dished.

  1. The bike originally came with a Suntour sprocket, which is only 7.5mm wide compared with the Dura-Ace sprocket I installed which is 9mm. So I could put a narrower sprocket back on, but I’m only 1.5mm better off.

  2. The original bottom bracket spindle was 109mm, so when it came to replace it I got the same size. I could simply buy a 118mm spindle (do they exist?), but I feel like it’s the wrong solution - aren’t spindles that size made for triple chainrings? The original cranks were JIS square taper, and Sheldon told me an ISO crank on an ISO spindle would send the chainring out 4.5mm - which it seemed to do (plenty of clearance to chainstay), but how accurate is this?

Errrgh…sorry for the essay, maybe I should just take it to my LBS. Any help would be appreciated.

from sheldon brown

If you install an ISO crank on a J.I.S. spindle, it will sit about 4.5 mm farther out than it would on an ISO spindle of the same length.

not sure if you misread sb or just mistyped?

edit: just read your older post and realised what you meant

Single sided track hubs are supposed to be built with some dish - a sufficient amount to centre the rim.

Then installation in different size rear ends would require symmetric spacing on either side of the hub. It looks like the dishing may be the problem.

The most common chainline is 42mm (i.e. generally manufacturers make their BBs and Cranks, and their hubs and sprockets such that they are 42mm). Check SB for peculiarities.

After reading your other post, your initial bb/crank combo looks about right at 41mm.
When you say the crank is really close to the chainstay, how close is really close? I’ve had a clearance there of about 2mm with no problems.
Then, what is the clearance on the other side - they should be the same.

It was so close there are scratches on the paint where they have hit. See below:

That image was with the original 130BCD JIS cranks on an ISO BB spindle. Now I have 151BCD ISO cranks on an ISO BB spindle - there is a comfortable clearance now. (According to Sheldon they would have come out 4.5mm.)

It’s so frustrating as I thought I was making it better but it has seemed to have got worse.

That is one way to know for sure that they are too close :).

What is your from chainline now? Is the BB 68mm?

p.s. Looks like that frame will need a blast/repaint if you want to keep it for a while… have you sprayed the inside of the tubes with fishoilene or similar?

I’d have to check the chainline measurement again, I really just used the chainring as a starting point as I’m pretty confident that is where it should be. Yes, the BB shell is 68mm.

You don’t like my patina? :smiley: Yes, the inside has received a healthy dose of fish oil. I would like to strip and respray it one day (much to the horror of patina lovers), but the budget didn’t extend that far this time around.

True, if you match the chainline at the wheel to the chainline at the cranks, it will be fine. But then you might have issues if you ever want to change the wheels or cranks to another bike. Set them both up for 42mm and you can swap parts around willy nilly.

Hahaha, that’s a little beyond patina! I live beside the ocean so even a patina is verboten in my house. I didn’t ride my road bike for about 3 months and the road grime on the chain rusted, seizing a few links and rendering the chain useless.

At the least, I’d get at that with a wire brush and then spray some fish oil on the outside too.

^ Good point. I’ll check where the chainline is at - sounds like a re-dishing is in order.

I just checked Velobase to see if those hubs were made for a narrower spacing, and noticed the spacer is on the sprocket side:

I don’t want to get the wire brush on it - the paint comes off pretty easy. I did hit it with fish oil after that photo was taken and it’s a lot better.

+1 thats the last place you want rust, eliminate it before it gets worse

So they are for 120 rear then?

Don’t know if you’ve seen this sheldon page but its got plenty of good info.

Last thing I’ll say because it’s your bike and you can do want you want with it, but the paint coming off easily is a sign that it needs work, IMO.

Yeah 120. I did read that SB page earlier on in the works, probably a good time for a refresher!

Fair call re: paint. Perhaps I’ll clean up the underside of the BB shell and just do a touch up job. I’m just worried if I start it won’t stop!

Thanks for all your help.