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Old 03-15-13, 05:55 PM   #1
twocicle
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Eccentricity: da Vinci / Bushnell discussion

I had posted this info in another build thread of mine, but Ritterview requested this to be a topic of it's own for clarity, so creating this new thread.

During my quest to outfit a new frame, I called Mel @ Tandems East to ask about the Bushnell and da Vinci EBBs (eccentrics).

Here is Mel's EBB lineup with #2 - Bushnell, and #7 - da Vinci:



Mark (tandemgeek on this forum) has the following background information discussing the 3rd gen Bushnell (#2 above) and da Vinci's involvement in its development. http://www.thetandemlink.com/article...eccentric.html

While I do not have both EBBs on hand to compare, mechanically they both seem identical. The most obvious visual differences of the da Vinci are the serrated "teeth" and hole cutout pattern. I took Mel's recommendation and went with the da Vinci which is posted on his website at a very reasonable $120. Other than Tandems East and da Vinci direct, I'm not sure who else is selling this EBB version.

My Feedback:

So far, usage of the da Vinci EBB has been very easy and surprising how little effort is needed to tighten the EBB sufficiently to keep it from slipping. Likely the teeth on this model provide more bite/grip in the EBB shell than a smooth surface (ie: Bushnell) would. I' am only guessing because no instructions were provided with the EBB and so a recommended "nm" torque setting is unknown. Perhaps this model would be the same as Bushnell, but I do not have that info. For now I'm using my "sort of firm" setting. After a few rides everything remained just as it was installed and no creaks or other pesky issues that sometimes can occur.

I am still a little concerned with all those drilled out holes letting in gunk and grime around the outside of the EBB shell, but at only 144gm and great grip without much apparent need for cranking on the expansion bolt, it seems like a keeper.

This is a photo of the installed da Vinci EBB:

Last edited by twocicle; 03-15-13 at 05:59 PM.
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Old 03-15-13, 06:46 PM   #2
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Go to http://www.bushnelltandems.com/ and click on the F.A.Qs link. There you will find a link to download installation instructions.
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Old 03-15-13, 08:48 PM   #3
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After 10K miles on our daVinci I don't find the spanner holes to have any great tendency to collect grit. Of course, the dark color of the eccentric makes the grit hard to see.
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Old 03-15-13, 09:01 PM   #4
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Go to http://www.bushnelltandems.com/ and click on the F.A.Qs link. There you will find a link to download installation instructions.
Egad! Point #7: "cinch the 4mm hex wedge bolt to 75-90 inch lbs (8.5-10 Nm)". I've only been doing the da Vinci to maybe 4-5Nm tops and no slip or creak. Good to know there is a lot more headroom to tighten if needed. Thanks.

BTW, the DV EBB is so easy to back off and turn, I don't bother to use any pin spanner to tighten the Gate CenterTrack belt. Just a quick twist with both hands on the Ultegra's external HTII cups and that is sufficient to get the belt tension set to the pluck tone range needed. The EBB also let me cheat the front cranks to the timing side by a millimeter or so without needing to use spacers on that side. Nice.
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Old 03-16-13, 05:09 PM   #5
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Mark (tandemgeek on this forum) has the following background information discussing the 3rd gen Bushnell (#2 above) and da Vinci's involvement in its development. http://www.thetandemlink.com/article...eccentric.html

While I do not have both EBBs on hand to compare, mechanically they both seem identical. The most obvious visual differences of the da Vinci are the serrated "teeth" and hole cutout pattern.
When I read that link, I'm inclined to think that daVinci provided engineering input to a Bushnell product, which in turn was made available to daVinci for their bikes.

Last September, our stoker eccentric decided to fail with 25-30 miles left on a weekend event ride, leaving the stoker to ride with a chain tensioned by her pedaling efforts. Some googling led me to the (mistaken) notion that our daVinci used Bushnell eccentrics, and that Bushnell was part of R&E cycles near UW in Seattle. The following Tuesday, I was wheeling our tandem in, hoping they could cure the endless ticking we'd been having.

The next day, I was told that I'd received a Bushnell eccentric free of charge, as the daVinci eccentric wasn't making proper contact with our frame, and that Bushnell was investigating the daVinci eccentric for patent infringement. I know nothing further regarding the state of those matters, but I'm certainly unhappy that the daVinci eccentric has less (and insufficient) gripping area in a daVinci frame than the Bushnell product it perhaps copied.
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Old 03-16-13, 09:58 PM   #6
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Originally Posted by twocicle View Post

During my quest to outfit a new frame, I called Mel @ Tandems East to ask about the Bushnell and da Vinci EBBs (eccentrics).

Here is Mel's EBB lineup with #2 - Bushnell, and #7 - da Vinci:
I took a screenshot from Tandems East's site, which includes the explanatory table.

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Old 03-17-13, 05:08 AM   #7
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Originally Posted by p2templin View Post
The next day, I was told that I'd received a Bushnell eccentric free of charge, as the daVinci eccentric wasn't making proper contact with our frame, and that Bushnell was investigating the daVinci eccentric for patent infringement. I know nothing further regarding the state of those matters, but I'm certainly unhappy that the daVinci eccentric has less (and insufficient) gripping area in a daVinci frame than the Bushnell product it perhaps copied.
Here's a thought, before making too many assumptions and assertions based on those assumptions, give Todd a call at daVinci and (a) see if you can learn why your eccentric may have been creaking, (b) what may have caused it to "fail", (c) understand more about the design of your original eccentric, and (d) gain some insight to balance what you were told at R&E about the design history & rights. It is true that R&E now owns all of Bushnell's former intellectual property and brand... and that you can usually find Dennis & Jenny Bushnell at R&E.

FWIW, the Bushnell eccentrics are also prone to creaking if they're not properly prepped and torqued, and then re-torqued now and again... noting we own/have owned tandems that have used four different models of the Bushnell eccentrics. BTW, how did your eccentric fail, i.e., what actually happened and what caused it? I only know of one failure mode for a Bushnell eccentric that I would assume is true for the daVinci and it requires the user to over-torque the tension screw.

Good on the folks at R&E (Dan?) for sending you on your way with a new Bushnell eccentric. R&E is an awesome shop.
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Old 03-18-13, 04:14 PM   #8
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Here's a thought, before making too many assumptions and assertions based on those assumptions, give Todd a call at daVinci and (a) see if you can learn why your eccentric may have been creaking, (b) what may have caused it to "fail", (c) understand more about the design of your original eccentric, and (d) gain some insight to balance what you were told at R&E about the design history & rights. It is true that R&E now owns all of Bushnell's former intellectual property and brand... and that you can usually find Dennis & Jenny Bushnell at R&E.

FWIW, the Bushnell eccentrics are also prone to creaking if they're not properly prepped and torqued, and then re-torqued now and again... noting we own/have owned tandems that have used four different models of the Bushnell eccentrics. BTW, how did your eccentric fail, i.e., what actually happened and what caused it? I only know of one failure mode for a Bushnell eccentric that I would assume is true for the daVinci and it requires the user to over-torque the tension screw.

Good on the folks at R&E (Dan?) for sending you on your way with a new Bushnell eccentric. R&E is an awesome shop.
FWIW; I did a lot of reading on ECC's before buying my last batch. Ended up buying the Bushnell (both the regular one and the lightened on). All have been rock solid and have experienced no creaking or slipping. Recommend using a torque wrench to install them to spec. If your bike has an outsized shell, you can get the shim from Rodbikes also.
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Old 03-19-13, 12:31 AM   #9
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On Sunday we waited until the afternoon for the temperatures to rise above 40F, but then rain squalls came in with wind and hail. After jumping in the car and driving to three separate locations to avoid as much rain as possible, we ended up 40 miles away in the Spokane Falls area to do a loop of 9-mile Falls. The roads were still very wet in many parts and with all the winter grit & gravel still on the roads, by the end of the ride our shiny new tandem looked more like we had ridden a roubaix tour. The drive chain was squeeking, our Speedplay cleats were squeeking and gritty, muck had built up between the chainstay and belt (luckily I had put framesaver there) and everything was caked with a sticky grime.

I disassembled much of the tandem today to give a thorough cleanse and sure enough the DV eccentric had let plenty of grit inside the shell area. The eccentric itself seemed clean enough in the internal parts so I didn't bother disassembling that at this point and just had to wipe down the exterior of it plus the EBB shell in the tandem.

I have the feeling this dirt penetration into the EBB will be an ongoing thorn I'll have to deal with. Thinking over of ways to plug up the gaps left open by the teeth on the edges and the so-called spanner holes which I have not needed to use for tightening the eccentric (hand rotation has been easy and sufficient).

Last edited by twocicle; 03-19-13 at 03:44 PM.
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Old 03-19-13, 03:58 AM   #10
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I am a bit confused by the concept of a serrated outer surface on the eccentric.

Is the intent to have the serrations "bite" into the frame to allow more holding power?

If so, wouldn't this make the frame almost a wear item?

Is the serrated EBB better for use with a belt drive that is preloaded? I had not heard of chronic issues of EBB slipping with a timing chain or timing belt.

What am I missing here, when comparing a smooth vs serrated EBB?

PK
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Old 03-19-13, 06:10 AM   #11
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Thinking over of ways to plug up the gaps left open by the teeth on the edges and the so-called spanner holes which I have not needed to use for tightening the eccentric (hand rotation has been easy and sufficient).
Silicone caulk for the spanner holes? Perhaps grease for the edge teeth?
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Old 03-19-13, 08:52 AM   #12
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I am a bit confused by the concept of a serrated outer surface on the eccentric.

Is the intent to have the serrations "bite" into the frame to allow more holding power?

If so, wouldn't this make the frame almost a wear item?

Is the serrated EBB better for use with a belt drive that is preloaded? I had not heard of chronic issues of EBB slipping with a timing chain or timing belt.

What am I missing here, when comparing a smooth vs serrated EBB?

PK
There are 2 physical principals at play here. 1) the friction force. someone made the following comment above

Quote:
I'm certainly unhappy that the daVinci eccentric has less (and insufficient) gripping area
Well, with regards to friction force, surface area has absolutely nothing to do with it. A wider doorstop is no more effective than one which is an inch wide.

2) Converting stress into force. So yes, the the serrated edge can "bite," but it will apply a greater localized normal force than a design like the Bushnell assuming same geometries and stress on the "wing." And since friction force isn't dependent on surface area contact, the greater normal force creates more friction force. Whether it "bites" into the bottom bracket shell depends on a number of factors - force at the tip of the edge and the material properties of the shell. My guess is, the shell is made of some type of stainless steel which has a similar hardness, or "harder" than the eccentric itself.

The weakness can then become the serrations themselves, but that is another topic for another day. You'll just have to trust the engineering was done.
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Old 03-19-13, 09:08 AM   #13
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There are 2 physical principals at play here. 1) the friction force. someone made the following comment above



Well, with regards to friction force, surface area has absolutely nothing to do with it. A wider doorstop is no more effective than one which is an inch wide.

2) Converting stress into force. So yes, the the serrated edge can "bite," but it will apply a greater localized normal force than a design like the Bushnell assuming same geometries and stress on the "wing." And since friction force isn't dependent on surface area contact, the greater normal force creates more friction force. Whether it "bites" into the bottom bracket shell depends on a number of factors - force at the tip of the edge and the material properties of the shell. My guess is, the shell is made of some type of stainless steel which has a similar hardness, or "harder" than the eccentric itself.

The weakness can then become the serrations themselves, but that is another topic for another day. You'll just have to trust the engineering was done.
Oh good, another forum member trashing my post. So thrilling.

Look: we own a davinci bike. It had a davinci eccentric. Based on what a very reputable shop told me (which has on staff/management the designer of the part), the eccentric wasn't making full and proper contact with the frame. Right about now, I don't give a darn about friction: the eccentric and frame were from the same company, and they couldn't figure out how to make them meet in the middle! Explain to me why I should call them to find out why, and explain to me why I should stop for a moment to consider the friction forces and such.

Oh, and by the way, you have a typo in the beginning of your post. There are no principals at play here, we aren't in school. In school, I learned that these were principles. And before you flame me for being anal-retentive, consider that accuracy in word choice is essential to any sort of technical explanation, which you were trying to do.
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Old 03-19-13, 09:20 AM   #14
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p2templin, since your clarification indicates that you apparently meant the middle of the EBB did not grip... take a look at the 7 EBBs pictured. Only #5 - Trek would have any significant grip in the middle and all the rest are apparently bad designs according to your report. At least, that appears to be what you are trying to indicate.

Your preference is confusing, because you apparently moved to the Bushnell (#2) and seem to like that, but it is otherwise identical to the da Vinci (#7) sans serrations on the shell interface surfaces.

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Old 03-19-13, 10:30 AM   #15
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Originally Posted by PMK View Post
I am a bit confused by the concept of a serrated outer surface on the eccentric.

Is the intent to have the serrations "bite" into the frame to allow more holding power?

If so, wouldn't this make the frame almost a wear item?

Is the serrated EBB better for use with a belt drive that is preloaded? I had not heard of chronic issues of EBB slipping with a timing chain or timing belt.

What am I missing here, when comparing a smooth vs serrated EBB?

PK
I am not qualified to address the technical aspects of friction such as localized force and swept area but I suppose the serrations would have the effect of making it look like it grips better and therefore have a happy customer.
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Old 03-19-13, 10:58 AM   #16
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I am not qualified to address the technical aspects of friction such as localized force and swept area but I suppose the serrations would have the effect of making it look like it grips better and therefore have a happy customer.
Todd would not bother in that regard. I can say that with very little tightness, the DV EBB gripped very well and did not slip during our rides. So in my experience, it does seem to work. Perhaps this info is of some value.
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Old 03-19-13, 10:58 AM   #17
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Oh good, another forum member trashing my post. So thrilling.

Look: we own a davinci bike. It had a davinci eccentric. Based on what a very reputable shop told me (which has on staff/management the designer of the part), the eccentric wasn't making full and proper contact with the frame. Right about now, I don't give a darn about friction: the eccentric and frame were from the same company, and they couldn't figure out how to make them meet in the middle! Explain to me why I should call them to find out why, and explain to me why I should stop for a moment to consider the friction forces and such.

Oh, and by the way, you have a typo in the beginning of your post. There are no principals at play here, we aren't in school. In school, I learned that these were principles. And before you flame me for being anal-retentive, consider that accuracy in word choice is essential to any sort of technical explanation, which you were trying to do.
please forgive the grammatical heirs. I was just trying to help. We're all not perfect, and I especially am not two particular about my righting when posting to online forums. The point was clear and communicated affectively. In school, I learned to play nice with others.

to address why you should call davinci when you have a problem with a davinci bike. you paid good money for the bike, and if something isn't working, perhaps they can help you sort it out instead of "trashing" them.

Good luck, hope all works out for you in the end.
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Old 03-19-13, 12:09 PM   #18
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Eccentrics are being used on fixed gear bikes. The mountain bike company Niner has [applied for] patented, developed and refined its own eccentric, the Niner Biocentric II. At 129 grams it is lighter than the Bushnell. It is specific for the Niner frame BB shell, and is sized and shaped somewhat differently. A tandem version of the Biocentric would be the easiest way to get a different eccentric into the game.



Niner ad copy:

Reliable Function - Traditional EBB units are held in place with set screws that can become difficult to finely adjust over time, or expansion wedges that can deform the bottom bracket shell of the frame. Split BB shells that clamp an EBB can stretch or ovalize. The BioCentric II avoids these troubles by using two bolts to apply a clamping force on the outside edges of the BB shell, eliminating the possibility of ovalizing or indexing the shell itself. Secure, quiet, easy to install and adjust, the BioCentric II will change your ideas about singlespeed drivetrain setup and maintenance.



Here's a video touting the Biocentric EBB (the earlier version with one screw)
[video=youtube;8FE1o-gs1qc]http://www.youtube.com/watch?v=8FE1o-gs1qc&feature=share&list=PL33F0AF449B3FBC0B[/video]
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Old 03-19-13, 12:54 PM   #19
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^^^ Calfee also has a two piece EBB, but there are issues with that design that the Bushnell style resolves.

1. The two piece can twist an misalign as you rotate it, so you have to be careful with that.
2. Adjusting BB cups and/or crankarm preload can be tricky, especially if using a belt which requires more tension than a chain. This is due to the two piece not having a fixed width of its own.. it needs to be tightened before you adjust the BB. Then you can't rotate the eccentric if you have a lot of preload or a BB than squeezes the eccentric.
3. The two piece has no lateral adjustment capability.
4. The only way the two piece stays in place is by squeezing the ends of the EBB shell. There is not a lot of surface area there, so the EBB slipping can be a problem. The thin green areas highlighted in the images above show just how little contact area there is with that design.
5. The two piece ends are not press fit, so they may move inside the shell when under load.

Last edited by twocicle; 03-19-13 at 01:00 PM.
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Old 03-19-13, 02:20 PM   #20
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^^^ Calfee also has a two piece EBB, but there are issues with that design that the Bushnell style resolves.
I had a Calfee eccentric, the inadequacy of which I believe led to the seizing of my bearings while climbing Ebbett's Pass on the Death Ride. No problems since switching to a Bushnell.

I had thought the Niner had some sort of secret mechanism for expanding outward against the inner sleeve, but in looking over the patent, no, it is apparently mainly the clamping force of bolts inward from the flange. That is consistent with the Biocentric being specific for the Niner shell, which has been designed to accomodate these forces. The Calfee appears to be a less refined example of this, and weighs the same, too.





It might be that Niner has figured out how to get a two-piece, external-clamping eccentric system to work, and if so, this of potential benefit for tandems.
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Old 03-19-13, 02:32 PM   #21
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^^^ The only obvious difference between the Calfee and Niner is that the latter has a fixed sleeve for each short bolt. While this may help somewhat with the twist issue I mentioned above, I doubt (FWIW) that would be sufficient to completely resolve that one point, and does nothing to help solve the others.

These two are so similar looking that I wouldn't be surprised if the Niner is encroaching on a Calfee patent (if they have one).

Using the Bushnell or DV at 144g seems to be the solid choice, though my DV may soon be adding a couple addnl grams of silicone chalk, and I expect the Bushnell would also let in grime through the spanner holes in their version too. If you are lucky enough to never ride in the conditions we did this last weekend, then this may be a non-factor for you. Otherwise, I am confident it would reproduce 100% of the time on everyone's tandem in the same conditions. I certainly do not enjoy or intend on riding in slop like that, but fate has its own plans.

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Old 03-19-13, 03:27 PM   #22
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I hate the Calfee EBB design...

I really need to take my bike apart and bring it to Calfee for the Bushnell.

I tried carbon grit paste, applied plenty of torque.. the thing still manages to creak/click/slip.
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Old 03-19-13, 03:46 PM   #23
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It is my experience that improvements in components specific to tandems are most likely to occur first in other cycling categories, and then be adopted by tandems, as almost all of these categories dwarf tandems in volume and no one is interested in developing components for tandems' miniscule numbers.

An example is the search for long length, hi-rise stems needed for stokers, which are found not for tandems, but for trial bikes, a category I'd not even known existed!

So, if eccentrics are to be improved, it will probably be for singlespeeds. See, here FSA has made a new eccentric, but certainly with no thought to tandems.

Quote:
Originally Posted by Bike Radar
Spurred on by some of its OEM customers[i.e. not tandems] , FSA has developed a new eccentric bottom bracket adapter that allows the use of singlespeed, belt, and internally geared hub drivetrains on frames with vertical dropouts and PressFit 30 bottom bracket shells.

The new eccentric adapter is very straightforward in design: the two adapter cups slip into the bottom bracket shell, two bolts tighten them down [looks like same concept as Niner and Calfee], and conventional external-type threaded bearing cups are then threaded in. Loosening the bolts allows for easy rotation in the shell to adjust the tension of the belt or chain.

FSA's new eccentric adapter will allow singlespeed, belt and internally geared hub drivetrains to be used on frames with vertical dropouts and PressFit 30 bottom bracket shells.

If FSA is developing a new eccentric, and using the Calfee/Niner two-bolts-squeezing-the-flange-inward method of purchase, then to some extent that constitutes an endorsement of the concept.

FSA's wont is to make components for niches, such as its tandem crankset with OEM customers. Might FSA be amenable to modifying its PF30 eccentric for tandems?
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Old 03-19-13, 04:55 PM   #24
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^^^ FSA's implementation is deliberate for a different and obvious reason... compatibility with a standard BB30 shell. Of particular uniqueness is how the offset of the eccentric is external to the shell. Still, the fact that it exists does not eliminate the existence of the problems listed above... no matter how many pretty rings they throw into the marketing mix.
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Old 03-19-13, 06:27 PM   #25
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Quote:
Originally Posted by p2templin View Post
Explain to me why I should call them to find out why...
You might learn something...
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