"Syncros" Bike. Which bottom bracket?

[vdmruss]

Hi All,

I am trying to change the BB on my MTB, but can't figure out which one to buy.

It's a "Syncros" bike from 2010 or around then. Mostly SRAM Components. The crank says "Rutkion". There are some markings on the BB, but they don't make sense.

There are plugs at both side that can be removed with an allen key. I think there is a spindle with notches inside, but haven't taken the crank arms off yet (by the way, how do they come off?).

I'm pretty skilled mechanically, can rebuild car engines etc, but surprisingly got stumped here as too much conflicting information as to how to measure it and way too many standards and variations. I ordered a tool with notches to remove it, hopefully it will get there soon - can't dismantle it further yet.

Are the brackets reverse threaded? Locktite?



Best Regards,
D

[trailgumby]

Howdy. Your image isn't displaying, unfortunately - might want to look at permissions settings.

[warthog1]

Howdy. Your image isn't displaying, unfortunately - might want to look at permissions settings.

I can see it on my android phone.
Looks like a threaded bb with external cups.

[trailgumby]

Are the brackets reverse threaded? Locktite?



Best Regards,
D

Pasting the link in my browser address bar let me see the image. Could be a Hollowtech style BB, but hard to tell from that angle.

Yes, one side is reverse threaded. Pedals, non-drive side. Threaded bottom bracket, drive side. The idea is they unwind in the direction of normal rotation, so they don't bind up with the passage of time and become impossible to remove.

[mikgit]

seems that's a Truvativ crank and has a splined bottom bracket, so probably ISIS, says Powerspline, so maybe that's their name for ISIS, or something else?
If so you would need to take the bolts off, then use a crank puller to get the cranks off (need a specific one for the type of crank/bottom bracket...so not one that fits square taper, but splined).
Then another tool to remove the bottom bracket.
Then the BB should have dimension on it.

But yeah, try to repost the picture, or see if you can figure out the full name of the bike...I'm 99.999% sure syncros didnt make bikes they are a parts company, so probably something else.

[vdmruss]

Thank you for your replies.

I will take some more pictures when the sun is out.

I did a bit of research, and it seems to be a bracket of this type:



The number markings seem similar.

However, these brackets are a bit hard to find and there are a lot of warnings that they seem to have changed the spindle from 24mm to a tapered 22mm/24mm spindle, and are quite expensive to take a punt.

I am wondering it its possible to re-use the spindle, and just get standard Shimano bottom bracket cups for a 24mm spindle?

Like this one:
https://www.ebay.com.au/itm/401949352576

I have yet to pull it apart to get final measurements, but it seems to be what I have.

[ironhanglider]

Thank you for your replies.

I will take some more pictures when the sun is out.

I did a bit of research, and it seems to be a bracket of this type:



The number markings seem similar.

However, these brackets are a bit hard to find and there are a lot of warnings that they seem to have changed the spindle from 24mm to a tapered 22mm/24mm spindle, and are quite expensive to take a punt.

I am wondering it its possible to re-use the spindle, and just get standard Shimano bottom bracket cups for a 24mm spindle?

Like this one:
https://www.ebay.com.au/itm/401949352576

I have yet to pull it apart to get final measurements, but it seems to be what I have.

I don't think that it is possible to remove the spindle from the pictured BB (without damaging it). Even if you do it is not designed to work with the BB in the ebay link. The linked BB is for cranks that have an integrated spindle.

Why do you need to replace the BB?

Cheers,

Cameron

[mikgit]

is the spline part tapered? If so, then worry. Is the axle itself tapered, as in 24 at the spline then taper down to 22, then back up to 24 on the other side, then probably less of an issue.
Was a dark time in BB's, in addition to the 2 frame with sizes (nin mtb) and all the axle widths, you then has square taper (still) and then octalink (2 of) and isis and i guess this powerspline thing... what a mess.

[vdmruss]

Well, no way to fix what I had. The bottom bracket isn't made anymore except for some ultra-wide downhill version which probably won't fit.

Couldn't get the non-drive side crank arm off the spindle either. It completely seized up, maybe it's doable with an impact wrench, but the puller had some weird non-standard socket between 1/2" and 3/8", so couldn't try that either. Bearing failed and detached from the cup.

Lucky the drive side came off easy and the non-drive side bottom bracket cup/bearing disintegrated, so ended up installing a new modern GXP bottom bracket and a used SRAM X7 crank. Working pretty well so far. The self-extracting mechanism on the X7 look pretty good too.

Buy the way, how are the X7 cranks & GXP bottom brackets for durability? The original Howitizer bottom bracket bearings are huge and have to be like 2X the size of GXP.

[Andy01]

Perhaps your puller is metric ? 3/8" = 9.5mm and 1/2" = 12.7mm, so you would have 10, 11 & 12mm in between. Or perhaps a 7/16" (which is not too uncommon) if it is imperial ?

[MattyK]

The idea is they unwind in the direction of normal rotation, so they don't bind up with the passage of time and become impossible to remove.

Actually the opposite - they're threaded so they don't unscrew themselves while you're just riding along. They will self-tighten as you pedal. (I am aware that the threading direction is counterintuitive to this)

[trailgumby]

The idea is they unwind in the direction of normal rotation, so they don't bind up with the passage of time and become impossible to remove.

Actually the opposite - they're threaded so they don't unscrew themselves while you're just riding along. They will self-tighten as you pedal. (I am aware that the threading direction is counterintuitive to this)

'
We will have to agree to disagree. Think about which direction in which the drag in your pedal bearings applies force to the pedal spindle next time you are removing them from the cranks. This is CCW (conventional thread) on the drive side - the same direction you apply the pedal spanner when you are taking them off.

Same on threaded BBs. The drag the bottom bracket bearing exerts on the frame as you pedal forward exerts force that would spin the Hollowtech bearing housing CW on the drive side. The same direction you apply the BB spanner when you are taking them off (ie reverse thread on the drive side BB). I am looking at a Shimano SM-FC6601 bottom bracket on the desk next to me as I type this to confirm.

[Duck!]

You will find it's to prevent unthreading. Case in point Italian-thread (road-only) bottom brackets; normal R/H thread both sides, the drive side is notorious for self-extracting.

[Tim]

Same on threaded BBs. The drag the bottom bracket bearing exerts on the frame as you pedal forward exerts force that would spin the Hollowtech bearing housing CW on the drive side. The same direction you apply the BB spanner when you are taking them off (ie reverse thread on the drive side BB).

I puzzled over this for some time a while back. I think you might be incorrect Trailgumby. MattyK and Duck have it right.
The force of the bottom bracket bearings are acting to tighten the BB cup on the drive side, in an anti-clockwise direction.
As MattyK stated it's counter intuitve. I'll explain.
The crank and spindle spin in a CW direction under power. The bottom bracket bearings correspondingly spin in an anti-clockwise direction. The anti-clockwise turning bearings are in effect pushing against the BB cup in an anti-clockwise direction. Tightening it against the frame.
Although the spindle is turning clockwise the force is transferred to the BB cup in the opposite direction because of the motion of the bearings.
I think.

[trailgumby]

Although the spindle is turning clockwise the force is transferred to the BB cup in the opposite direction because of the motion of the bearings.
I think.

Yeah, nah. How can the angular direction of the force being applied reverse? The section of your quote I've bolded breaks the laws of physics.

Try visualising what happens when the inner race turns clockwise against the fixed outer race in the image below. The drag from point of contact between the bearing ball surface and the inner race pulls the ball in a clockwise direction, and friction with the fixed outer race causes the ball to spin counter-clockwise while travelling in a clockwise direction (albeit at half the revolutions of the inner race). They transmit drag (force) on the outer race outer race in a clockwise direction.



Lets take an extreme example and crank the bearing drag up to 100%: superglue the bearing solid so the balls cant spin in their cages, and then superglue the bearing to the spindle, so that the crank spindle is locked solid to the threaded BB bearing housing via the bearing. Turn the drive side crank clockwise on the drive side. Does the BB tighten or loosen? It's a reverse thread on the drive side. It loosens.

By using grease instead of superglue you change (reduce) only the magnitude of the force transmitted by the bearing to its housing, not its direction.

Does that make more sense?

[trailgumby]

You will find it's to prevent unthreading. Case in point Italian-thread (road-only) bottom brackets; normal R/H thread both sides, the drive side is notorious for self-extracting.

Which part?

[Duck!]

The obvious one.... Cup/housing in the frame.....

[Tim]

Try visualising what happens when the inner race turns clockwise against the fixed outer race in the image below. The drag from point of contact between the bearing ball surface and the inner race pulls the ball in a clockwise direction, and friction with the fixed outer race causes the ball to spin counter-clockwise while travelling in a clockwise direction (albeit at half the revolutions of the inner race). They transmit drag (force) on the outer race outer race in a clockwise direction.

Image

At this point we need an engineer or physicist to step in and clear things up.

But I still stand by my uneducated opinion.
Here's where I think you are wrong:

"...friction with the fixed outer race causes the ball to spin counter-clockwise while travelling in a clockwise direction.."

It's friction from the moving inner race (crank spindle) that causes the ball to spin counter-clockwise. The inner race is "driving" the ball in a counter-clockwise rotation. The outer race is resisting the force applied to it from the "driven" ball. The friction applied to the outer race is pushing in the opposite direction to the inner race, potentially pushing the outer race in a counter-clockwise direction.
The sum total of my high school physics inattention taught me that for every action there is an equal and opposite reaction.

[MattyK]

We will have to agree to disagree. Think about which direction in which the drag in your pedal bearings applies force to the pedal spindle next time you are removing them from the cranks. This is CCW (conventional thread) on the drive side - the same direction you apply the pedal spanner when you are taking them off.

Same on threaded BBs. The drag the bottom bracket bearing exerts on the frame as you pedal forward exerts force that would spin the Hollowtech bearing housing CW on the drive side. The same direction you apply the BB spanner when you are taking them off (ie reverse thread on the drive side BB). I am looking at a Shimano SM-FC6601 bottom bracket on the desk next to me as I type this to confirm.

Yes we disagree, because you're wrong. Sorry. Not trying to be rude about it, just clarify a common misconception.
The major forces are from precession due to clearances between the mating parts. The effect of friction in the bearings is insignificant in comparison.

Feel free to argue with Sheldon and Jobst if you prefer.
https://www.sheldonbrown.com/brandt/left.html

[Tim]

Ah, so I was wrong too. Oh well.

[trailgumby]

Try visualising what happens when the inner race turns clockwise against the fixed outer race in the image below. The drag from point of contact between the bearing ball surface and the inner race pulls the ball in a clockwise direction, and friction with the fixed outer race causes the ball to spin counter-clockwise while travelling in a clockwise direction (albeit at half the revolutions of the inner race). They transmit drag (force) on the outer race outer race in a clockwise direction.

Image

At this point we need an engineer or physicist to step in and clear things up.

But I still stand by my uneducated opinion.
Here's where I think you are wrong:

"...friction with the fixed outer race causes the ball to spin counter-clockwise while travelling in a clockwise direction.."

'
The only way for your assertion about the balls reversing the direction in which torque is applied to the outer race is for the ball cage to fixed in place to act as a fulcrum for the balls to brace against.

That is not what happens. Watch this video from the six second mark, and re-read my comments.

[trailgumby]

Feel free to argue with Sheldon and Jobst if you prefer.
https://www.sheldonbrown.com/brandt/left.html

They're both dead.

I'll read up on precession, though.

[MattyK]

https://en.wikipedia.org/wiki/Precession_(mechanical)

[Duck!]

Perhaps your puller is metric ? 3/8" = 9.5mm and 1/2" = 12.7mm, so you would have 10, 11 & 12mm in between. Or perhaps a 7/16" (which is not too uncommon) if it is imperial ?

Shouldn't matter, crank pullers, and cranks that need them are a standard thread. Oversized & hollow spindles such as ISIS and Octalink need a plug for the crank tool plunger to push on, but many crank tools will include it. The only point of difference between brands of tools is that some use a 15mm spanner, while others use 16mm.

[Andy01]

Perhaps your puller is metric ? 3/8" = 9.5mm and 1/2" = 12.7mm, so you would have 10, 11 & 12mm in between. Or perhaps a 7/16" (which is not too uncommon) if it is imperial ?

Shouldn't matter, crank pullers, and cranks that need them are a standard thread. Oversized & hollow spindles such as ISIS and Octalink need a plug for the crank tool plunger to push on, but many crank tools will include it. The only point of difference between brands of tools is that some use a 15mm spanner, while others use 16mm.

I assumed that the poster was referring to the size of the socket (or spanner) required to turn the puller "shaft" and was trying a 3/8" or 1/2" socket and found that the correct size was somewhere in between - which could be a few metric sizes ? Maybe a "standard" puller tool (2 jaw or 3 jaw ? ), and not a specific crank puller ?

Perhaps I read that wrong ?