Chain ring hitting frame

Hi,
just got a singlespeed crankset for the fixed-gear conversion I'm working on, and the chain ring is hitting off the frame. I didn't expect that, hasn't happened to me before. The other crankset i was using didn't have this problem. Can anyone enlighten me as to what's going on? Are certain cranks incompatible with certain bottom brackets or something?

thanks.

it does indeed seem it's the wrong b/b for the crank...

What was the frame in it's old life? Some mbts struggle with a 42 mm chainline (with large rings).

Did you buy the b.b and crank set to give you a 42 mm chainline or have you just got the crank set and are tring it on the b.b that was on the bike?

Was the crankset new, if so the documentation should tell you what length b.b will give you what ever chainline. You may have to alter the length off b.b you buy to obtain the decired chainline.

yes, if you run a really narrow 102mm BB with something design for 111mm. can you put the chainring on the outside of the crank? without screwing up chainline.

most BB are around 107mm ish so something designed for 111 isn't an issue.

The frame was a Raleigh Record Sprint road bike. I'm using the bottom bracket that came with it. I also have the original crank, but was planning to use a nicer looking singlespeed one I picked up cheap 2nd hand.
I've also been having chainline problems, so maybe I should try to sort out a combination of BB/crank that will give me the right chainline? Or maybe just go back to the original crank. (The ss crank won't allow for mounting the chainring on the outside).
So I guess I'm trying to use a crank that's designed for a longer BB. bugger.
I've done a couple of ss conversions without any chainline/bb problems, this is my first fixed gear, seems to be a much trickier proposition.

I'm using a 103mm BB to give a 42mm chain line, I had to crimp the drive side chainstay further than it was to give clearance for the chainring. bear in mind being a MTB frame I have clearance for about 52mm rubber!

where is it hitting the chainstay and what is the frame made of.

just buy a new wider BB from wiggle, can get cheapo for £10-15 ;)

be warded that diffrent cranks require diffrent b.b to get the correct chainline but dogsballs in right work out the b.b you need and get a new one.

i assume he can work a tape measure/verniers to measure shell width and current spindle width

I had to crimp the drive side chainstay further than it was ......
I must confess that I don't know what this means. (The frame is cro-moly by the way).

yes, if you run a really narrow 102mm BB with something design for 111mm

I haven't measured it yet, but it does look very narrow. That probably explains it then.
Been reading what Sheldon Brown has to say about bottom brackets/cranks (http://www.sheldonbrown.com/bbsize.html). I'm planning to bust out the vernier calipers tonight (yes, he can work them, my years teaching university physics students how to use them will stand me in good stead here), and see what my required chainline is.
If I understand correctly, by measuring the current spindle length, and the front chainline I get with the different cranks I have, I should be able to work out what length BB will work with which crank to give the required chainline (assuming the bugger doesn't bang off the chainstay).
thanks for enlightening me on the esoteric world of bottom bracket/crank compatabilities.

In laymans terms, crush the tubing of the chainstay until there was clearance for the chainring!

there was already an area that had been crimped/dented to clear the 32 tooth chainring, I extended this crush along the chainstay until I had enough clearance for the 42tooth ring. I used a combination of vice (to do the crushing), small piece of steel round bar to act as a dolly to crush against, pliers to hold the dolly and a piece of softwood to prevent crushing the back of the chainstay. paint flaked a bit but other than that I'm very happy with the job, I brazed in new track ends so the paint needed doing anyway.

Also: If you put a JIS crank on an ISO BB, it'll go further down the spindle than intended.

mr_tom Also: If you put a JIS crank on an ISO BB, it'll go further down the spindle than intended.

i'm somehow quite sure this is the case here... but then if you put a JIS crank on ISO BB the spindle will stick out too much you won't really be able to tighten the cranks properly.

and if the BB is the original that came with the bike since it rolled out of the factory 20+ years ago it must be ISO.

what cranks you using? it's definitely worth swapping out the BB for one that'll fit properly.

Ok, I've made some measurements, and it's starting to look like my inexperience has caused me to acquire a selection of parts that don't go well together. Here's what I've got:

• back wheel built on a flip-flop hub with 120mm axle spacing
  
• frame with 127 mm dropout spacing
  
• BB spindle 117mm
  
  

the hub gives a rear chainline (using 120mm locknut spacing) of about 37mm. the shortest front chainline I can get (using the original cranks) is 39mm. seems close, but it looks noticeably off, and is noisy as hell. currently stumped, and grateful for any advice that may be forthcoming.
(chainline aside, I assume I'm also going to have to do something about that 7mm difference between the dropout spacing and the hub spacing. note to self: do homework before buying parts)

Can you space the front chain wheel in, I had my first setup with a shimano MTB crank, with the 44t chainwheel on the inside of the spider where the 32t one normally goes, then spaced it in further on some washers gave me quite a decent chain line (providing the chainwheel doesn't hit the chainstay). you could also fit a spacer behind the rear sprocket to bring it out a mm or so.

Are you sure it is a 37 mm industry standard is 42 mm Goldtech are 45 mm 37 seem very strange. How are you measuring the chainline? Is there any documentation that tells you what the chainline should be approx.

No documentation I'm afraid. The hub is a TX Quando (like the flipflop hubs on this page http://www.ktgroup.net/pro_bmx.htm#). Here's how I measured the chainline:
locknut-locknut = 120mm
locknut-center of sprocket = 23
chainline = ((120)/2) - 23 = 37
Assuming I'm doing this right (which is a big assumption), for the chainline to be 42mm, then the locknut-sprocket would have to be 18mm, and it definitely isn't.

I already have the chainring on the inside of the spider, and it's only a mm or 2 from hitting the chainstay as it is. Fitting a spacer behind the rear sprocket is a good idea, assuming there's enough thread there to play with I suppose?

Just checking you are mesuring the correct distance, the locknut i.e the nut which the inside of the dropout butts up against to the center of the cog. Can't find any thing in google to say that TX Quando should be that far off.

Poorly done pic here but the distance marked is ment to come from the inside of the drop out.

Yep, that's what I'm measuring alright (cheers for going to such trouble to illustrate the point!).

hmm I can't offer any more advice than BillB I am afraid, I was just suprised to see such a strange chainline.

I would suggest trying to get a 1mm spacer for your rear sprocket with the lockring on it should hold in place plenty well enough, then if you have 2mm of space between the front ring and chainstay shim it in a mm with some spacers, HubJub do some .6, and 1.2mm spacers, I got some spring washers from my local fastenings place and filed a flat onto one edge, they worked a treat.

Ok, I'll give that a go. Thanks for the tips. I was stumped, now I've got something to try.