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Old 08-26-12, 05:24 PM   #1
JonathanGennick 
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help identify bottom bracket

A friend gave me the following bottom-bracket. What exactly do I have? The labeling says 73E, but the threaded section is easily a centimeter wider than one of my 73mm bottom bracket shells. The entire unit is 130mm wide. What sort of bike is this thing for?
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Old 08-26-12, 07:13 PM   #2
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I think it is for a 73mm wide bottom shell for e-type derailleur for a isis splined MTB-crankset. I f you account for the 2 mm ring of the etype derailleur on the drive side and push in the non drive side the roughly 8mm adjustable (the golden part in your picture) then you have the 10mm difference you measured. (If you don't know what an e type front derailleur is look under google pictures). This is a bottom bracket for a special MTB set up, the chance you will need this is small.
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Old 08-26-12, 07:43 PM   #3
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It's an 73mm, E type, FSA Platinum DH ISIS bottom bracket. The right cup is modified for an E-type front derailleur where a derailleur bracket connects to the right side with a ring between the right cup and shell, spacing the BB cup further out and the spindle is spaced back 2.5 mm on the drive side. As far as the BB cup width, it appears the left cup has not been pushed all the way on the cartridge.

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Old 08-26-12, 08:46 PM   #4
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Ok. I do know what an e-type derailleur is. But I held that thing up against a frame today having a 73mm shell, and there is no way that thing could be tightened down without a good centimeter of spacers.

I'll take a second look tomorrow though. Maybe I there is something I missed seeing earlier today.
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Old 08-26-12, 09:09 PM   #5
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Ok. I do know what an e-type derailleur is. But I held that thing up against a frame today having a 73mm shell, and there is no way that thing could be tightened down without a good centimeter of spacers.

I'll take a second look tomorrow though. Maybe I there is something I missed seeing earlier today.
Your photo shows the left cup not bottomed out on the cartridge; it should be covering the shinny ring, which is a cartridge bearing and is pressed in when you tighten the left cup.
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Old 08-26-12, 09:16 PM   #6
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Your photo shows the left cup not bottomed out on the cartridge; it should be covering the shinny ring, which is a cartridge bearing and is pressed in when you tighten the left cup.
I thought I had pushed it all the way on when I held the thing against the frame. The cup slides back and forth easily enough. There's a bit of air trapped in there though, and it pops back out like in the photo when I'm not holding it.
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Old 08-26-12, 09:36 PM   #7
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I thought I had pushed it all the way on when I held the thing against the frame. The cup slides back and forth easily enough. There's a bit of air trapped in there though, and it pops back out like in the photo when I'm not holding it.
The last 8-9mm is taken up when the cup is press over the exposed cartridge bearing during installation. Don't try and do this outside the BB shell or it will be hell trying to get it apart again. If you look at the Bottom Bracket you can see how much of the cartridge the right cup covers; this is how much the left side will cover once installed and the cup is pressed over the bearing.

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Old 08-26-12, 09:40 PM   #8
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The last 8-9mm actually press the exposed cartridge bearing into the cup. Don't try and do this outside the BB shell or it will be hell trying to get it apart again.
Really? That's interesting. What an odd design. Normal bottom-brackets don't press their bearings when you tighten them down.

I might pop it into the frame tomorrow and tighten 'er down just to see what happens.
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Old 08-26-12, 10:58 PM   #9
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Really? That's interesting. What an odd design. Normal bottom-brackets don't press their bearings when you tighten them down.

I might pop it into the frame tomorrow and tighten 'er down just to see what happens.
Not as abnormal as you would think. When ISIS was being developed there was a need to somehow make up the difference in the bearing size because of the enlarged spindle. The answer was to use cartridge bearings that didn't stop at the inside of cartridge, but extended out to the cups; if you pull off the left cup you will see two cartridge bearings being held on by a thick aluminum ring (the standard is 3 bearings, one on the left and two on the right or drive side). With one bearing on the left side the cup will seemingly stop about 2mm short of bottoming out because the bearing runs up against small lip on the inside of the cup so the bearing has to be pressed in to that lip during installation. Yours has two bearing on the left side, so the need to press the bearings into the cup is simply more obvious.

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Old 08-27-12, 05:45 AM   #10
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might be for an 83mm or 100mm bb width of some DH bikes
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Old 08-27-12, 06:44 AM   #11
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Carved out some time to install this bottom-bracket to see how things played out. Image #1 (below) shows the shell width at 73mm. (Actually, it's a bit less. Maybe it was faced once upon a time).

Image #2 shows the installed unit. I've bottomed out the left cup. You can see more spindle showing on the left. The spindle measures to between 129mm and 130mm using my calipers. With the calipers spread across the spindle ends, the center-point of my shell falls at about the 160mm mark. So the thing is off-center.

I did install a single, 2.5mm spacer driveside to simulate an e-type derailleur.

Image #3 shows that about 3mm of threads protrude on the non-drive side.

The bottom-bracket is marked 73E MM. The shell is 73mm. Yet the bottom-bracket does not fit well.

Enlightenment is welcome. I've learned a few things already from digging into this.

Image #1: Shell is 73mm


Image #2: More spindle on non-drive side


Image #3: About 3mm extra threading on non-drive side
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File Type: jpg bb01.jpg (97.1 KB, 13 views)
File Type: jpg bb02.jpg (94.1 KB, 14 views)
File Type: jpg bb03.jpg (99.2 KB, 12 views)
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Old 08-27-12, 10:50 AM   #12
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Carved out some time to install this bottom-bracket to see how things played out. Image #1 (below) shows the shell width at 73mm. (Actually, it's a bit less. Maybe it was faced once upon a time).

Image #2 shows the installed unit. I've bottomed out the left cup. You can see more spindle showing on the left. The spindle measures to between 129mm and 130mm using my calipers. With the calipers spread across the spindle ends, the center-point of my shell falls at about the 160mm mark. So the thing is off-center.

I did install a single, 2.5mm spacer driveside to simulate an e-type derailleur.

Image #3 shows that about 3mm of threads protrude on the non-drive side.

The bottom-bracket is marked 73E MM. The shell is 73mm. Yet the bottom-bracket does not fit well.

Enlightenment is welcome. I've learned a few things already from digging into this.



Image #2: More spindle on non-drive side
The primary issue here is your BB shell is not just a bit less, it is 1.5mm too narrow. If you look at the wide aluminum ring on the left side, you can see that when it was last installed about 1.5 mm more of the ring was covered, which would have been the case had the shell been the proper width; it would also make up some of the threads that are protrude on the non-drive side. The fact that the spindle is not symmetrical is not uncommon; since this BB is for a DH crank, usually these cranks use a straight (not curved) left arm for more strength and the stays are wider, so the left side needs to extend out more than usual.
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Old 08-27-12, 11:29 AM   #13
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The primary issue here is your BB shell is not just a bit less, it is 1.5mm too narrow.
No, it's not that bad. I just checked w/a caliper. The caliper reads 73mm, maybe just a touch under in spots. I guess you have to choose whether to trust the tape or the caliper in this case.

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The fact that the spindle is not symmetrical is not uncommon; since this BB is for a DH crank, usually these cranks use a straight (not curved) left arm for more strength and the stays are wider, so the left side needs to extend out more than usual.
Ok. That's interesting to know.

If I put two spacers drive-side, it looks like I can get the spindle centered. Since I have nothing much better to do while awaiting the correct bottom-bracket in the mail, I might play around with this one, center it, slap on the cranks, and see how it looks.

I've no idea what the frame was designed around, but I've been running a 113mm spindle. Going to 130mm is a big jump. Chainline will probably be a disaster.
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Old 08-27-12, 12:15 PM   #14
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No, it's not that bad. I just checked w/a caliper. The caliper reads 73mm, maybe just a touch under in spots. I guess you have to choose whether to trust the tape or the caliper in this case.



Ok. That's interesting to know.

If I put two spacers drive-side, it looks like I can get the spindle centered. Since I have nothing much better to do while awaiting the correct bottom-bracket in the mail, I might play around with this one, center it, slap on the cranks, and see how it looks.

I've no idea what the frame was designed around, but I've been running a 113mm spindle. Going to 130mm is a big jump. Chainline will probably be a disaster.
I just had another idea that skipped my mind because I don't have a downhill bike. Most of the downhill bikes have chainguides which require either a special chain guide rated BB or an E-type. I don't have the time to look into it right now but my guess is this bottom bracket was previously set up with a chain guide attached to the BB and an additional spacer to widen the chainline to 50mm.
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Old 08-27-12, 12:53 PM   #15
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I just had another idea that skipped my mind because I don't have a downhill bike. Most of the downhill bikes have chainguides which require either a special chain guide rated BB or an E-type. I don't have the time to look into it right now but my guess is this bottom bracket was previously set up with a chain guide attached to the BB and an additional spacer to widen the chainline to 50mm.
I feel like I'm doing forensic bike science here, or maybe bike archaeology.

The guy who gave me the part -- and it was a year or more ago -- is a BMX parent who somehow ordered the wrong bottom-bracket by mistake. He held onto it for a couple years, never did anything with it, and threw it a me.
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Old 08-27-12, 03:31 PM   #16
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The fact that the spindle is not symmetrical is not uncommon; since this BB is for a DH crank, usually these cranks use a straight (not curved) left arm for more strength and the stays are wider, so the left side needs to extend out more than usual.
All ISIS BBs are symetrical.
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Old 08-27-12, 04:39 PM   #17
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All ISIS BBs are symetrical.
When I said The fact that the spindle is not symmetrical is not uncommon, I was referring to the fact that with an adjustable chainline (in this case adding or subtracting spacers behind the fixed cup) the spindle may not be equal on both sides; the spindle is symmetrical in the cartridge but the cups and spacers can change it's orientation in the shell. However you are right to say I didn't explain it very well..
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