Bicycle Mechanics - New Bottom Bracket, now I have chain clearance issues.

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2k2S4
09-04-03, 12:30 AM
I'm still rebuilding my old Schwinn 564 road bike. I purchased a new Shimano BB-UN53 cartridge BB to replace the old Shimano unit that came on the bike 15 years ago. The old BB was a 68x117.5 unit so I purchased the UN53 in the next closest size, 68x118, thinking that it would fit. Well, I finally got around to installing it and the crank arms tonight, and I found that there is no way this is the correct size. After torqueing down the crank bolts, there is only a few mm of clearance between the small chainring and the chainstay, definitely not enough for a chain to fit on the chainring.

The strange thing is that there is plenty of room on the opposite (left) side of the bike. It looks almost like in installed the bb backwards, but I've checked and rechecked, I didn't. Things are threaded correctly. Does anyone have any idea what's going on? What could I be doing wrong?

NZLcyclist
09-04-03, 12:38 AM
have you got the same chainrings as before?

I have minimal clearance on my bike too, but the chain never goes on that part of the chain ring? yes? no? it's only an issue when you get some chain suck where it carries tyhe chain up the ring instead of chucking it across to other ring.

Brendon
roadfix
09-04-03, 01:03 AM
Originally posted by 2k2S4
.....there is only a few mm of clearance between the small chainring and the chainstay.......
Nothing wrong with that......although long B/B spindles are for triple chainrings, I believe. Is your crankset a double or triple? Check to see if your crank ends are evenly spaced on both sides against the chainstays. If they are, you should be fine.