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Single Speed Junkie
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Types of Eccentric bottom brackets?

Have seen a few types of bottom brackets over the years and curious why the set screw type seems to distort the frame (where the set screws are pressing against the bottom bracket it self) when torqued down to spec.? And does this damage the frame?
 

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Good question. I'm not sure because I have a pinch bolt EBB but I'll speculate nonetheless...

I wonder if the frame's BB shell has more to do with the distortion than the EBB insert per se. Various frame materials (that is, BB shell material) might allow for variance in the likelyhood of distortion. Plus the individual framebuilder's choice of shell thickness, regardless of material, may be a factor.

Finally, I imagine it's easy for some of us riders to get a bit hamfisted when tightening things like set screws, causing us to over-torque them. (I know how easy this is to do as I over-torqued my pinch bolt EBB once and snapped one of the brazed-on fittings off the shell.) With a set screw type EBB, it seems like this factor might cause a BB shell to distort (especially over time) when perhaps it would not have distorted if properly torqued throughout the frame's lifetime.

--Sparty

crux said:
Types of Eccentric bottom brackets?

Have seen a few types of bottom brackets over the years and curious why the set screw type seems to distort the frame (where the set screws are pressing against the bottom bracket it self) when torqued down to spec.? And does this damage the frame?
 

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Just curious Crux, how many of these distorted shells have you seen? Judging from the wall thickness of "normal" BB shells, this occurrence seems unlikely. However, I haven't actually surveyed wall thickness of EBB shells. It makes sense that they could be thinner than a wall that needs to support threads ("normal" BB shells). I have only had my SS bike for 3-4 months and have had to readjust BB just once so far, so your post raises some flags for future consideration.

One possibility may be what Sparty mentioned in the hamfisted department.
I know that most people and even a lot of bike shops haven't made the investment in torque wrenches. Having had a shop in the past, I feel that this is one of the best tools to get new mechanics to develop a feel for the correct amount of force to use when fastening things down. In my experience, most new mechs use either an excess of force, or nowhere enough. They don't cost alll that much and when properly cared for will last a lifetime; while saving a lot of broken parts.
 

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Mine distorted enough that it started to slip regularly. (And yes I use a torque wrench.) The Ti BB shell was to soft and the location of the set screws didn't help either. If the set screws wouild have been placed at 12 o'clock, it may not have been a problem. The shell is currently being replaced under warranty with a Bushnell setup.

jw

crux said:
Types of Eccentric bottom brackets?

Have seen a few types of bottom brackets over the years and curious why the set screw type seems to distort the frame (where the set screws are pressing against the bottom bracket it self) when torqued down to spec.? And does this damage the frame?
 

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My steel problem solvers shell used for my Marlin conversion is plenty beefy and I had no problems until one of the nuts fell off due to poor brazing. I rode the bike for a few miles on the road and managed to deform the shell a bit (though not visibly) enough that the eccentric no longer moves freely in the shell. 15 minutes in a mill should solve the problem, but for now, I'm just going to ride it as is because the RIG is my main squeeze.

YO MAMA
 

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Agree with the hamfisted scenario. Just went through the process of helping a friend with building a custom SS.
The frame builder was quick to point out that too many people get over zealous and over tighten BB and etc feeling it's necessary to torq them down. This often leads to damaged parts/frames down the road.

Mudflaps said:
Just curious Crux, how many of these distorted shells have you seen? Judging from the wall thickness of "normal" BB shells, this occurrence seems unlikely. However, I haven't actually surveyed wall thickness of EBB shells. It makes sense that they could be thinner than a wall that needs to support threads ("normal" BB shells). I have only had my SS bike for 3-4 months and have had to readjust BB just once so far, so your post raises some flags for future consideration.

One possibility may be what Sparty mentioned in the hamfisted department.
I know that most people and even a lot of bike shops haven't made the investment in torque wrenches. Having had a shop in the past, I feel that this is one of the best tools to get new mechanics to develop a feel for the correct amount of force to use when fastening things down. In my experience, most new mechs use either an excess of force, or nowhere enough. They don't cost alll that much and when properly cared for will last a lifetime; while saving a lot of broken parts.
 

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The fact is, all eBB types distort the shell a bit when tighten, since they all rely on friction to hold them in place. With pinch and setscrew types, the distortion depends on how close the ID of the shell is to the eBB insert diameter. I have 2 set-screw frames, one shows virtually no gap, the other shows a large gap - because the ID tolerances were poorer on one. I ended up converting the poor fitting one over to a Bushnell (I personally like the Bushnell eBB design better).
 

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Agreed

itsdoable said:
The fact is, all eBB types distort the shell ....
I like the idea of an expanding insert like the Bushnell or a contracting shell a la pinch bolts for the same reason you cite. These EBB systems are designed to bring the surfaces into closer contact with one another around the entire perimeter of their interface. The pinch bolt design does so in the same way a stem clamps onto a fork's steer tube, which forms a close-tolerance grip that actually conforms the surfaces to one another rather than distort them.

That said, I believe that there is nothing wrong with the set screw type EBB so long as insert and shell are machined to be very close-tolerance.

--Sparty
 

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Based on builders recommendation...this is what we went with on my gerls new SS.

FYI - The builder added the personalized security system, a la "Tink". :)

Sparticus said:
I like the idea of an expanding insert like the Bushnell or a contracting shell a la pinch bolts for the same reason you cite. These EBB systems are designed to bring the surfaces into closer contact with one another around the entire perimeter of their interface. The pinch bolt design does so in the same way a stem clamps onto a fork's steer tube, which forms a close-tolerance grip that actually conforms the surfaces to one another rather than distort them.

That said, I believe that there is nothing wrong with the set screw type EBB so long as insert and shell are machined to be very close-tolerance.

--Sparty
 

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The 12:00 solution?

GrumpyOne said:
Mine distorted enough that it started to slip regularly. (And yes I use a torque wrench.) The Ti BB shell was to soft and the location of the set screws didn't help either. If the set screws wouild have been placed at 12 o'clock, it may not have been a problem. The shell is currently being replaced under warranty with a Bushnell setup.

jw
Here's a photo of the EBB on my Burley tandem; probably doesn't take the abuse of a SS, but it is certainly well made and the set screws are at the 12 o'clock (OK, maybe 1:00) position. Also my Rocklobster with a split shell variety; it has never been a problem and I'm sure the quality of the welding is a big factor. I can't imagine anyone with disc brakes going with anything else.

1G1G, Brad
 

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Wow

That looks stout! And cool...

I've seen your gerl's recent post of her bike as well as your recent post of your gerl (along with her bike)... way nice on all accounts.

Coincidentally, I happen to call my Baby Tinkerbell as well, or even more often I just call her "Pixie." She can fly. (And I ain't sayin' nuthin' else. :eek:)

--Sparty

Burdman said:
Based on builders recommendation...this is what we went with on my gerls new SS.

FYI - The builder added the personalized security system, a la "Tink". :)
 

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tks. yeah, it's pretty cool and was a very nice touch and surprise that the builder added.

appreciate the comments; i took a risk by posting the pics of my gerl and her new ride, but i couldn't help it....i'm a happy and proud guy...and feel very fortunate to have a gerl that loves to go riding and wants MTB parts and etc for Christmas! :D

Sparticus said:
That looks stout! And cool...

I've seen your gerl's recent post of her bike as well as your recent post of your gerl (along with her bike)... way nice on all accounts.

Coincidentally, I happen to call my Baby Tinkerbell as well, or even more often I just call her "Pixie." She can fly. (And I ain't sayin' nuthin' else. :eek:)

--Sparty
 

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Ain't it great? Pixie got a new custom Vulture this summer after riding gears for years. She's taken to riding SS like nobody's biz. I've gotta take some pix of her bike and put 'em up here. Her bike's got custom haze-blue 'wavy water' theme paint that glows in the dark (no shite, she does plenty o' night riding up here in Oregon's winter darkness) plus her sled's loaded with nuthin' but the best parts... all silver from stem to rims, including a "white" carpet fiber seatpost.

The thing's dang near too pretty to get dirty.

Talkin' 'bout the bike right now. :eek:

I better get outta here. Gettin' distracted.

Oh boy.

--Sparty

Burdman said:
tks. yeah, it's pretty cool and was a very nice touch and surprise that the builder added.

appreciate the comments; i took a risk by posting the pics of my gerl and her new ride, but i couldn't help it....i'm a happy and proud guy...and feel very fortunate to have a gerl that loves to go riding and wants MTB parts and etc for Christmas! :D
 

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Sparty...get some pics of your pixies ride for us to see...it sounds awesome! Tink wanted to come over to the dark side of SS and I think she's really going to hammer too. Although, the too dang pretty to ride thought has grabbed her as well and she said there's some trails she doesn't want to take her new "duty beauty" for fear of scratching it!
We'll see about that.... ;)

Sparticus said:
Ain't it great? Pixie got a new custom Vulture this summer after riding gears for years. She's taken to riding SS like nobody's biz. I've gotta take some pix of her bike and put 'em up here. Her bike's got custom haze-blue 'wavy water' theme paint that glows in the dark (no shite, she does plenty o' night riding up here in Oregon's winter darkness) plus her sled's loaded with nuthin' but the best parts... all silver from stem to rims, including a "white" carpet fiber seatpost.

The thing's dang near too pretty to get dirty.

Talkin' 'bout the bike right now. :eek:

I better get outta here. Gettin' distracted.

Oh boy.

--Sparty
 

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Sparticus said:
Her bike's got custom haze-blue 'wavy water' theme paint that glows in the dark (no shite, she does plenty o' night riding up here in Oregon's winter darkness)

take night shots, if you can!! got a black light? i'd love to see the thing glow!! i LOVE glow & the dark stuff!!!

The thing's dang near too pretty to get dirty.

I hear that. I feel the same way about my new ride. hope she has fun!! `
 
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