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Discussion Starter · #1 ·
So I started assembling my Mach4C. I put enduro bearings in the bottom bracket. Then I tried to put the crank shaft (Race Face Next SL) into the bottom bracket. It slid easily through the first bearing but when it got to the second it stopped. I had to hammer it a bit to get it through that bearing. It left me a bit uneasy. I checked both bearings and their flanges were making full contact with the bb shell. I was suspicious that something was out of allignment. With micrometer I measured the width of the shell including the flanges at two opposing positions and and found it to be different by about 0.8mm. Which meant that the ends/faces of the bb shell were not parallel! I pushed out the drive side bearing and with the crank still sitting in the bb held by non drive side bearing I tapped it back in. I used the shaft of the crank as a guide. I tapped it in such a way that on the "narrower" side of the bb there was about 0.8mm gap between the bearing flange and the bb shell. Sure enough the shaft of the crankset was sliding with ease now through both bearings. I find it rather incredible that pivot would screw up so much and make the two faces of bb shell not parallel. The manual of any bb says to press the flanges firmly untill there is no visible gap against the bb shell. I guess it does not work on my frame. I am planning to contact Pivot and mail them photos of my findings. Problem is that I got the frame on Ebay as new from a stripped bike. I wonder if Pivot will honor the warranty.

IMG_4577.jpg
The gap between the flange and the shell can be seen on the top. Without the gap the bearing is not squared and the shaft does not slide easily. WFT?
 

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LBS Manager
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I wish the industry would go back to threaded bb shells I absolutely hate press fit particularly bb 92. To me pressing a cheap piece of plastic into an expensive frame in not a good solution.
 

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Here, diagonally!
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I don't get it either. If it is to save on production costs, that is sad when frame + shock is > $2000.

To the OP: Agree having the gap is wrong, and I would check with Pivot to see what their position is on an Ebay frame. That being said, if it was mine I'm sure I could figure out how to enjoy a long and happy life with it. Might involve surfacing the shell and/or epoxy.

I am glad you are sharing. It is a data point for buying things off Ebay, and also for PF BBs. Doesn't mean either are deal breakers, but something folks should be aware of.
 

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Discussion Starter · #5 ·
It is all carbon.
 

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Elitest thrill junkie
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I wish the industry would go back to threaded bb shells I absolutely hate press fit particularly bb 92. To me pressing a cheap piece of plastic into an expensive frame in not a good solution.
One reason is your stiffness to strength is much better for a 30mm axle, which allows the stupid-light Next cranks. PF30 is fine, just all the stupid plastic POS SRAM BBs were not. Put a decent BB in there and it's fine.
 

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LBS Manager
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The race face BB is better but the whole BB 92 standard is flawed. I can live with BB30 (not pf30) but then the race face BSA 30 threaded BB is even better
 

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Are you talkin to me?
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Why don't you just have the BB shell faced? Sounds like that would solve all your problems.
A good bike shop can help you with that.
Just say-in!
 

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Are you talkin to me?
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You can face and ream carbon just as you can alloy. I had a local bike shop install a Chris King headset into my carbon bike frame and they used a reamer and facing tool before installation of the cups.
The carbon is real durable.
 

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Discussion Starter · #11 ·
You can face and ream carbon just as you can alloy. I had a local bike shop install a Chris King headset into my carbon bike frame and they used a reamer and facing tool before installation of the cups.
The carbon is real durable.
Wow! I would never suspect that. Thx!
 

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I've been following the thread for a few days and wanted to clarify a few questions/concerns. For starters, please contact Pivot and we can get this resolved for you. An email or phone call is all you need to do to get things resolved. Actually, contacting Pivot is always the 1st recommended step as we can generally resolve issues like this a lot faster than through MTBR or any other online forums or social media. We are always here to help and although we go through great steps to make sure that every frame is 100% perfect, we are still human beings and thus capable of the occasional missed detail.
That said, the facing operation is handled by a CNC machine so this should not happen. Please contact us and we will make it right. 1-877-85-PIVOT (74868) or [email protected].

Whether the BB is faced correctly or not has zero to do with a press fit or threaded BB. Facing is a separate operation and every type of BB should have parallel faces. This is normally a non-issue for Pivot but is something that many manufacturers fight with threaded BB shells as the machinery for facing threaded BB shells is not as precise and bonded in threaded shells on carbon frames are not normally faced at all after bonding.

Regarding press fit in general, we take a strong engineering based stance on why we use press fit. This design has served us well as it continues to give us more space to work with and allows for wider pivot placement, and larger down tube cross sections for a stiffer, stronger, and lighter frame. Executed properly, it also offers better control over the chain line, improved bearing alignment and supports the bearings better. Of course the design also allows us to mold a full carbon frame without bonding in an aluminum BB shell. This is one of the main reasons why it has become the industry standard for carbon frames. From a carbon frame design standpoint, it is superior. However, it does require very tight tolerances which Pivot is able to hold. Unfortunately, not all companies and factories are as precise and it can lead to problems. It’s interesting, however, as a threaded shell that is not done correctly has its own issues that lead to creaking BB's, bearings that are not well aligned, drivelines that are not straight and chain-lines that are out of spec. Both threaded and press fit BB's are excellent designs if executed properly and installed properly as well. In the case of Pivot, we run tighter tolerances than most in the industry and the press fit design allows us to build a better bike overall. From a purely engineering design standpoint, a threaded BB on a carbon frame requires the frame to basically have an open through hole with about the same amount of carbon supporting it and tolerance as the press fit design. Then the manufacturer needs to bond in a threaded BB shell. This machined shell usually has a separate left and right side and the parts mate with each other. These parts can be mis-aligned with each other, and the bond can creak and come loose over time. It’s a round shell inside a round hole so there is no mechanical lock between the two, other than the bonding area. It works fine most of the time, but (in general) it is still the highest warranty failure area for manufacturers running threaded shells in their frames. Even if that was perfect, the frame is now heavier and it has a narrower threaded shell bonded inside your frame so that you can now have bearing cups. The bearing is pressed inside the cup with threads hanging off the cups that screw into the bonded shell inside the frame. (even reading it sounds strange) These cups hang outside the frame and are leveraged outside the frame which leads to higher stress loads on the cups, bearing, and threads, plus its heavier. If your car or motorcycle were made this way, it would be heavier and less reliable.
It’s ok to put bearings directly inside the linkage, inside your hubs and even in your headset, so why doesn’t it make sense to do it inside your BB? Well, it does make sense. It just needs to be done correctly, with the right tolerance, the right installation procedure and the right BB design as well.
Hopefully this answers any questions regarding the press fit BB design and we look forward to resolving your issue.
Ken B (Pivot)
 

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Discussion Starter · #14 ·
THANK YOU PIVOT !! I will contact you.
 

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Elitest thrill junkie
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Ok, but BB92 is still retarded.
 

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LDC is ded,deth by trollz
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Ok, but BB92 is still retarded.
Actually as Ken stated its the premier BB standard. Scott, Pivot, BMC, Trek, Giant and many others know what works and thankfully they dont listen to internet forums. Pf92 is the gold standard of BB shells. Wider, stronger, more power to the rear wheel. He gave you the engineering reasons.


Sent from my SM-G360P using Tapatalk
 
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That detailed response from Pivot above is why my last two bikes have been Pivots as well the others in the future. As you can read they went to customer satisfaction first then explained the reasoning on why they do what they do.
Thank you :thumbsup:
 
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That detailed response from Pivot above is why my last two bikes have been Pivots as well the others in the future. As you can read they went to customer satisfaction first then explained the reasoning on why they do what they do.
Thank you :thumbsup:
Ditto. I have found the same attitude at my dealer as well. It's a main reason I am getting a new vault in the next couple of weeks.
 
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