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-   -   Modern BB question. Chain rings seem too close? (https://www.bikeforums.net/classic-vintage/317926-modern-bb-question-chain-rings-seem-too-close.html)

Bikedued 07-06-07 07:00 PM

Modern BB question. Chain rings seem too close?
 
I took my Voyageur frame in to get a nice cartridge BB installed. I guess there are no threaded spindles left out there, but no biggy I had some crank bolts around that fit. Anyways, I got the arms all tightened up, and the left side sticks out further than the right, like the spindle is backwards. The small ring is about 1/8" or possibly a tiny bit less from the chain stay. Can one of these newer style spindles be installed backwards, so that the longer side is on the wrong side? Should I not sweat it? The crank arm end to chainstay clearance is about the same as other bikes I have, just the center seems too close. Both ends of the crank arms are the same distance from the stays as well. For what's worth, the bike is an 81 Voyageur with stock Super Maxy cranks. It's going to bother the crap out of me, unless someone can tell me different. This is the second time it's been in this shop. The first time I didn't bring the crank with me, and the ends of the spindle were too short to keep the chainring off the frame.,,,,BD

Bikedued 07-06-07 07:08 PM

I will upload a pic or two in a while, the battery in the cam is too low to snap one right now.,,,,BD

vpiuva 07-06-07 07:18 PM

What length spindle did you end up with?

Bikedued 07-06-07 07:21 PM

Not sure, my wife had to take it in. I sent the old spindle in with it, along with the chainring side of the cranks. The first time they put a 113 in, this time I didn't get the box with the swap.,,,,BD

Bikedued 07-06-07 07:28 PM

2 Attachment(s)
Here's a pic, the cam just got enough charge. Second pic is an idea that hit me earlier today. Using an old steel handlebar plug to keep mud and water out of the steerer tube, hehe. Not sure if it's been done before, but I thought it was pretty neat.:D ,,,,BD

John E 07-06-07 09:26 PM

That left crank doesn't look very far seated onto the spindle, almost as though it's an old ISO on a JIS.

Bikedued 07-06-07 09:29 PM

Well, the drive side sunk down farther than I thought it should, which led me to believe the spindle was flipped.,,,,BD

repechage 07-06-07 10:09 PM

first, check the chainline, a STRAIGHT section of stock placed against the inside of the large chainring with chain and cage out of the way should land at the center
of the freewheel cog range, you will have to make a guesstimate of the thickness of your straightedge to locate "center" but if it is good, then be happy. if not then you will have to think it through, and not have a significant other take it in for service.

jgedwa 07-06-07 11:06 PM

yes, the spindle can be installed reversed. We fixed people do it all the time intentionally to help bring the chainline in. (And, by the way, on several of mine I would kill to have the chainline you ended up with.)

Leaving aside any chainline issues it may have created for you, there is no problem whatsoever to installing them that way.

Are your rings too close to the stays? Most definitely not. Rings can flex quite a bit, but not in that direction at that point in their rotation. If it clears at all, then you will never have trouble with it.

So, about chainline. I would not be surprised if this did significantly alter your chainline from ideal. There are two solutions if it did. The easiest would be to simply take out the spindle and reverse it. Or, what I think is the better solution would be to make lemonade out of lemons. Keep the spindle as is, and then re-space and re-dish the rear wheel to bring it back in line. The closer your chainline is to the center of the bike, the more evenly the rear axle is weighted. If you are heavy or if you have a rear freewheel with a huge off-set, this is a worthwhile modification to make.

jim

cuda2k 07-06-07 11:16 PM

Looks like the built in cup is on the drive side and the plastic second cup is on the non-drive side, which is the correct arrangement. Now could the spindle have been installed at the factory backwards... possibly. However aren't most modern BB's symetrical lengths? In any case, my best suggestion is to get a 1 or maybe 2mm spacer for the BB to put on the drive side.

JoeRivBob 07-06-07 11:37 PM

I have a Campy Centaur triple crank on its appropriate AC-H BB and it does the same thing. The crank-arm ends are equidistant from the chainstays, the chainline is good and the small wring is an appropriate distance from the frame. Works for me, but it freaked me out when I first noticed it.

vpiuva 07-07-07 08:45 AM

FYI: your fork plug doesn't only keep crud out - it keeps whatever water gets in, in. I'd drill a weep hole.

jgedwa 07-07-07 09:28 AM

Whoops, for some reason I had it in my head that you were talking about a non-cartridge BB.

I am not sure if it is reasonably possible to take the spindle out of a cartridge and reverse it. I do know that some of them can sort of be pried open and serviced, and so I presume the spindle could be switched around, but I have never do it.

jim

Bikedued 07-07-07 01:18 PM

Well, it was mostly for dressup. This bike will never see pavement if there's even a gray cloud in the sky, much less mud or water. It's too nice for that.;). I guess I'll wait for it to cause a real problem, and avert my eyes from the extra spindle on the left side.,,,,BD

DMF 07-07-07 02:09 PM

Modern cartridge BBs are (nearly?) all symmetrical, meaning that the length of each side is determined by the requirements of the crank. It may look weird, but it does keep the tread symmetrical.

If you want an asymmetrical spindle, you have to specify more than the length:
http://harriscyclery.net/merchant/37...ge/spindle.jpg

Harris Cyclery should have some asymmetrical spindles available.

cudak888 07-07-07 03:11 PM

Looks to me as if he could use a spindle about 2/3mm wider - when anyone starts pedaling down hard on that crankset, either the frame flex or the crankset flex will send that inner ring gnawing into the chainstay.

-Kurt

Bikedued 07-07-07 03:23 PM

That's it, it's going to the shop tomorrow, and it's getting changed again. I can't believe they had the crank and the spindle to look at, and didn't think that was too close. Thanks for weighing in, Kurt.,,,,BD

cudak888 07-07-07 03:41 PM


Originally Posted by Bikedued
That's it, it's going to the shop tomorrow, and it's getting changed again. I can't believe they had the crank and the spindle to look at, and didn't think that was too close. Thanks for weighing in, Kurt.,,,,BD

Ehhh! Shops will always do it to you - send you off with the wrong part for the sake of making a buck. They put the spindle in, found out that it just barely cleared, and instead of replacing it with a longer one, they figured they'd just send you off with this one, figuring that if you came to the shop to have the BB put in, you'll be too stupid to realize that the crankset is too close (and heck, if it worked their way, they wouldn't have to re-do the whole BB all over again - possibly even order another BB cause they don't have the longer one in stock).

Take care,

-Kurt

jgedwa 07-07-07 04:40 PM

I hesitate to disagree with Cuda, and I am not so much trying to get the OP to not get the BB replaced, but still on principle, I have to say that the ring will not flex at that point in its rotation, so it will never hit the stay.

I put together and sell a small number of fixed gear conversion bikes, and I always try to get as close to the stay as possible to keep the dish on the rear wheel to a minimum. Ideally, I want the wheel to have no dish whatsoever. In several cases, I have gotten the ring to within 1mm of the stay. The bike I ride every day is this close to the stay and I have never hit it. And I am a fairly big and strong rider, so if anyone could flex the ring, I could.

jim

cudak888 07-07-07 04:44 PM


Originally Posted by jgedwa
I hesitate to disagree with Cuda, and I am not so much trying to get the OP to not get the BB replaced, but still on principle, I have to say that the ring will not flex at that point in its rotation, so it will never hit the stay.

I agree that it is unlikely that the crankset will flex, but it is not impossible that the frame will flex enough to cause the chainstay to run into the ring. Has happened to me with 2mm to spare when not being ridden.

Take care,

-Kurt

USAZorro 07-07-07 06:35 PM


Originally Posted by cudak888
I agree that it is unlikely that the crankset will flex, but it is not impossible that the frame will flex enough to cause the chainstay to run into the ring. Has happened to me with 2mm to spare when not being ridden.

Take care,

-Kurt

Kurt, Jim, Bikedued,

Frame flex seems to get me too at times, and I'm not that big. 1/8" clearance isn't going to rub very often, but if you have to jump out of your saddle to get away from a dog or something, there's a fair chance some grinding will occur.

Hope the LBS doesn't give you crap when you get this worked out.

Bikedued 07-07-07 06:47 PM

They shouldn't really. They swapped out the first one they put in without too much hassle. I'm in there a lot, so once they see the clearance they'll probably see what I mean. 1/4" would be acceptable, but this is just a bit too close for comfort.,,,,BD

A year ago I flexed a full Crmo Team Mongoose enough to throw the chain. If a 20 inch frame would flex that much, imagine these longer non CrMo stays whipping around if I get on it, hehe.

jgedwa 07-07-07 07:04 PM

Far be it from me to beat a dead horse, but I stand on the following claim:

-if a ring under no force can make it all the way through its rotation without rubbing, then it will always make it around without rubbing. Sure rings and spiders can flex, but they will not flex at that point in the rotation. Sure rings and spiders can be bent, but then the antecendent clause of my claim would not be met.

-So that leaves frame flex. Okay, I will admit that different frames will bend in different ways, so I should not make absolute claims here. But since the ring would intersect the right stay just inches from the BB shell, I highly doubt that even a gorrilla could hammer the pedals hard enough to get a couple of mm's of flex only 3 cm from the BB shell.

jim

John E 07-07-07 07:09 PM

With Campa. Veloce cranks and my admittedly soft Capo frame, I was able to get the inner ring to rub the chainstay under torque. That frame definitely needs a bit of flex clearance. :)

jgedwa 07-07-07 08:36 PM

I stand corrected then.

Tomorrow's project for me will be to try to muscle up a hill so hard I can do it too!


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