Is This Right?

[1FJEF]

Specialized MTB 3x7 speed from about 1997-98.

The JIS square taper sealed cartridge bottom bracket is a Tange. It's marked BC 1.37x24T. Also 68 & a little sticker with an E. It measures 111mm wide. The right (drive side) has a flange, or lip that snugs up when you tighten. The left side does not, just outside threads, an inner shoulder snugs up to the cartridge as you tighten.

The bottom bracket on the bike measures 68mm if I remember correctly. But there is this additional funky silver plate, 3mm thick, that holds up the front derailleur & looks like it has two unused threaded holes. So in effect, the bottom bracket dimension is 71mm.

So (finally) here's my questions:

1) Does that funky silver plate that holds the FD look stock to you guys? Is it some kind of combo chain gaurd/FD mount that someone added?

2) Can I replace the Tange with a Shimano UN-55? Since the Shimano seems to have a lip on the left non-drive side adapter, wont the UN-55 end up with a 3mm gap between the end of the BB cartidge & the fastner (Shimano calls it "adapter") that retains it?

The left side has no lip & is flush when tightened:


I know you guys have all seen this, but here's the left side adapter:



Here's that funky silver plate, retained by the BB cartridge:

[DaveM]

1) Probably. The extra holes were probably either for chainguard or a chainkeeper device to keep the chain from falling off. It may be that they were never "intended" to be used for anything. The bike manufacturer just spec'd the derailleur because it was cheap and available at the time.

2) Are you sure the left side cup on the new BB has a lip on it? There shouldn't be one. These are pretty standard in that the right side has a lip and goes tight against the frame and the left side just snugs up against the BB cartridge. Shouldn't be any problem replacing with a UN55 BB as long as it has the same dimensions.

[1FJEF]

(06-15-2012, 02:50 PM)DaveM Wrote:  2) Are you sure the left side cup on the new BB has a lip on it?

Yes I believe so. The pictures I've seen of the Shimano UN-55 seem to show one.

[DaveM]

(06-15-2012, 08:10 PM)1FJEF Wrote:  Yes I believe so. The pictures I've seen of the Shimano UN-55 seem to show one.

Ah, I see what you mean. That lip probably isn't designed to snug up against the frame. Probably more intended to add some extra material around the tool fitting. The spacing on the BB is made so there will be a little bit of space in a 68 mm BB shell. However, with that front der. you have pushing the right side over a few mm, it could shift it enough that the left cup hits the frame before hitting the cartridge of the BB itself.

Couple options
- Just try it, there may be enough clearance even with the front der.
- Get a BB for a 73mm shell instead of 68. You may end up with a little weird offset on the cranks, but will definitely be wide enough.
- Use a 68 but use the left side cup from the old BB. This may work, but hard to know until you have the shimano BB in hand to test.
- File the lip off the left side cup before installing if it does bottom out.

Tough to recommend any particular option because there's a lot of little factors that could go one way or another.

[1FJEF]

(06-15-2012, 08:47 PM)DaveM Wrote:  Couple options
- Just try it, there may be enough clearance even with the front der.
- Get a BB for a 73mm shell instead of 68. You may end up with a little weird offset on the cranks, but will definitely be wide enough.
- Use a 68 but use the left side cup from the old BB. This may work, but hard to know until you have the shimano BB in hand to test.
- File the lip off the left side cup before installing if it does bottom out.

Tough to recommend any particular option because there's a lot of little factors that could go one way or another.

I thought about removing the lip. The diameter of the Tange & Shimano cartridges are slightly different I believe. I guess I could just get another Tange but I'd like to try the UN-55. They make it in 68 x 110mm.

[RobAR]

Hi 1F. That drlr is called an 'E-type' and the reason for its use is on non-traditional frames (oval seat-tube, etc) where a band-type (round clamp) will not work. That plate is how it is mounted - between the shell and the BB cup.
The holes that you are questioning are additional mounting locations for bikes that have something there to reinforce the drlr. Not all bikes will have that.
You're going to need an E-type BB. That's why the little 'E' sticker on your Tange. A Shimano BB will have the E designation after the model number (UN-40 E for example). On these, the right side cup is extended and has a flat between the threads and the flange. This is to fit the drlr to.

[1FJEF]

(06-16-2012, 09:30 AM)RobAR Wrote:  You're going to need an E-type BB. That's why the little 'E' sticker on your Tange. A Shimano BB will have the E designation after the model number (UN-40 E for example). On these, the right side cup is extended and has a flat between the threads and the flange. This is to fit the drlr to.

You are a veritable wealth of information. I didn't even see that information on Sheldon Browns site.
I have also not seen BB cartridges with an "E" designation listed on line either, most of my LBS aren't real helpful, they just want to sell bikes. They want $40-$50 for a UN-55 that's $19 delivered online. I have 30 years in retail, I don't mind spending 5, 10, or 15 percent more + tax to go local, but double to triple + tax chaps my hide.

[RobAR]

Yep, E-type BBs are getting to be rare as most bike mfrs are incorporating Direct Mount systems into frames that can't have a band-type FD mounted. You'll probably have to search for a NOS one somewhere.
Question - your seat-tube looks round in the pic. Is it?
If so, why not just upgrade the FD? They're pretty inexpensive.

[KC-Steve]

RobAr, . . . a wealth of information! I've often thought that but wasn't real sure.

Steve

[1FJEF]

(06-16-2012, 11:07 AM)RobAR Wrote:  Question - your seat-tube looks round in the pic. Is it?
If so, why not just upgrade the FD? They're pretty inexpensive.

The seat tube measures 35.2 to 35.6mm (measured at 3 or 4 different spots). The FD would have to be low enough to clear the water bottle area as I have something mounted there.
I would need to find one that would work with the bottom pull cable too, right?

[RobAR]

A 'Top Swing' drlr should clear the bottle bosses. Top Swing Bottom Pull is common.
I would consider your measurements as round. Heck, paint can make it vary that much!

[RobAR]

Well Steve, thx for the vote of confidence, buddy! I wish I had a wealth of something ($$ Hint). All I have is 30 yrs worth of bike info rattling around in a brain bucket. lol

JEF - honestly bro, I detested E types when they came out in the 1990s. No adjustment possible. It was a patch-fix that has since been resolved. Do yourself a favor and get a real FD. Those E part get scarcer every year.