chainring vs chainstay (clearance!!!)
 

i just changed out the crankset on my fixed gear bike. as it is, the teeth of the chainring are very very very close to the chainstay. less than a mm between. the chainring is a 43 tooth and i doubt a 44 would even fit. i am wondering if this is going to cause any problems. obviously the easiest way to find out is to find the steapest hill in town and charge up it with all my might -- to see if there is any flex thatll cause the teeth of the ring to dig into the chainstay. but unfortunately i dislocated my shoulder last week and need to take it easy for a month. BUT when i do get back to it i want my bike to be all ready for me. so- to those who know or those wanting to speculate, i ask: is this a cause for concern?

You may need a different bottom bracket. http://www.sheldonbrown.com/chainline/ for chainline. Is the chain straight with the rear sprocket? Is it a fixed gear conversion? Sight down the chain from the rear of the bike and see if the sprocket/chainwheel are on the same plane. Sounds like the chainwheel needs to go further out.

Mark

indeed, a mm of clearance might cuase issues, it would suck if a tooth was bent, though with the force hitting the frame its probably going to bent the tooth and not the frame. What size is your BB?

You should have changed the BB spindle length to match the new crank. 1mm isn't enough.

the frame is a 1940s era french track frame and the chainstays have been spread to accomodate a contemporary rear track hub (from 110mm to 120mm). as far as i can guess, the odd lack of clearance is caused by this. the chainline is about 2mm off but i have reason to deal with it (if you know the headache of old french bikes and also the particular predicament of my bb shell -- lets just say that for now i can put up with a slightly off chainline).

please just assume this is the best possible situation, since all i really want to know is: will the frame flex under load and cause the chainring teeth to rub the chainstay? maybe i will just have to wait out my convalescence and try it myself, but id like to hear some educated guesses from you bike mech gurus out there... oh and save a bit of touch-up paint.
:)

ehhh. ok. on to plan 'b' i guess. yeah i am avoiding changing the bb (which for the record is a 113mm) because of threading issues. actually when i remove the shimano english threaded bb, i dont know what threads will be left of the french shell. as it is, the bb is tight and problem-free. i am somewhat at a loss as to why that is..

plan 'b':

right now i have a road crankset on there and the chainring is on the back of the spider. this gives me a chainline that is off by -2.5mm. moving it to the front adds 7mm, so it is off +4.5mm. the solution, as i see it would be to get a 109mm bb (or a phil wood 111mm) and put the chainring on the front (which looks nicer anyway). that would fix my chainline and add at least another mm clearance.

anyway i am planning on taking the bb out today and trying to assess if plan 'b' will be that simple or if i will have to resort to plan 'c'.

plan 'c':

if the threads are totally ruined then i guess my only options are, either: 1) tap the shell to italian -- assuming i can find someone who i trust to do it for me (not anyone in town). or: 2) get one of those threadless bbs?? i dunno.

A guess is all it would be. Why not just flip a coin?

i probably will. why is that not enough? incipit neurosis.