so i found a thread where dustinlikewhat was having a problem that's basically the same problem i'm having now...installed some cheapie bmx cranks (a little holdover till i get the profile ones i was talking about in another thread). from the center of the seattube to the center of the teeth on the chainring is 52mm, instead of 42. i'm not sure they're on all the way, so i'm going to try a 107mm bb and chainring spacers to bring them in closer...

now, from dustin's old thread, it seems i need to find a bb with an iso taper spindle to go with bmx cranks. but that they could also maybe be jis.

so i guess what i'm looking for here is a little input on whether it seems like i'm going about this right.

edit: also, i'm only really trying to get this within 5mm of chainline. perfect is, of course, ideal, but if it's 2 or 3mm off, meh, whatever.

what's the current bb? Also, how big of a chainring (clearance issues)?

44t...there doesn't seem like there'd be any clearance issue there. the bb, i'm sorry to say, is a length i don't know. it's whatever was in the bike when i got it. i have, however, read several places that 107mm is a good size, so i'm going to start there.

What size BB are you using now?

Wait, if you've installed them now on some random BB and know you got a 52 mm chainline, you should be able to measure the current BB, no?

finding out what size bb you have and buying based on that would probably be a better solution than randomly getting a 107.

i wish i knew. i may have to take it to the lbs tomorrow and borrow calipers or somesuch tool.

hmmm, hey, how would i do that? i'm not that great at mathy stuff. so bmx cranks are typically set up for about 43mm chainline with a 107mm bb, correct? if i'm at 52mm, then i'm 9mm off. so i'd have a 116mm bb spindle now?

thing is, i'm not sure they're on all the way. i'm not sure if i need to tighten them on there to get them on all the way...it looks like the tapers aren't matched.

Take the BB out. You're going to need to do it to put the new one in anyway, and it's not like you can ride the bike now. Then you can measure it with any old ruler. Also see if it's symmetrical.

assuming both old and new BB are symmetrical, your new one would need to be 20mm less, because they are sized by overall width, so you have to double the change to figure the movement of one side. However, you need to torque it down to accurately figure out the current chainline, though you could just knock off a mm or 2

If your BMX cranks are anything other than JIS taper I would be VERY surprised (maybe some old campy BMX cranks aren't). Get a SHORT spindle, as short as you can, a lot of folks have to put that chainring on the inside of the spider to get a good chainline with BMX cranks.

i think i must need a different taper, then, to get my cranks on all the way...and i probably will need a much, much shorter spindle.

but, the current bb is coming out tomorrow (i'm not going home tonight...hello, booze!)...but i'll measure it tomorrow...i think tomorrow i'll be riding the bus with the bike (****, i hate riding on transit) to the lbs with borrowable tools to **** around with thigns a little, and be back with an update.

i love how every time i think i have a good idea, i check with you cats, and you have details and suggestions i should have, but haven't, thought about.

so i haven't been able to spend a lot of time on this the last couple of days, and i haven't gotten the bottom bracket out (lack of proper toolage)...but all the little tricks i've tried for measuring it all say the same thing: 145mm. that is ****ing insane. i'm still not sure i'm measuring right.

Does it have threaded bolt looking things on the end? Some older BB's have threads on the BB and use crank nuts rather than crank bolts. Measuring with those included would give you something like 145 mm. And for real, get yourself a $3 plastic vernier caliper and measure from the ends of the taper. You can also measure the actual chainline much more accurately with this tool -- measure the diameter of the seat or down tube, divide my 2, and then measure the distance from the outside of the tube to the chainring and add that on. Trying to eyeball the center of the tube is a recipe for crap measurements.

Is there possibly somebody in portland who can loan this cat a crank puller and a set of BB tools for like an hour and get this mess straightened out? This has gone on far too long.

I think portland has the best crank-pullers owned per capita numbers in the country.

here's how I solved my chainline problem:

Step 1.) Get drunk
Step 2.) Get out your 14mm socket wrench, or 10mm allen wrench, depending upon bolt
Step 3.) Crank to hell
Step 4.) Explain to your roommate, who doesn't care about bikes, in great detail how you solved your problem

so yeah, it seemed that I just didn't have mine tightenned down as far as I could, which may be a solution for you. But if it appears that your out of spindle to tighten on to, then I wouldn't go farther than step 1.

wow, I can't beleive I've been refrenced in a post, I feel all squishy...

ha, was that your solution?

as far as borrowing tools...i just have to suck it up and take the frame on a bus or something and i'm good. i just hate knowing i have to go across town to borrow tools and i can't ride. i mean...i can ride and carry the frame, but it'd rather not, and i can't ride the frame now.

yep, because when i first put the cranks on the bike was on a stand, which wouldn't let me get enough leverage. So with the bike on the ground and me leaning over it cranking on the bolt, I could put more force on the bolt, which ended up pulling the crank arm in about 5mm, which was what I needed.

yeah, it got mine close...i just need to change it so instead of just having single stack bolts on there, i'll have longer bolts and use washers to push it in as though it were the inner chainring on a double.