A question about bottom bracket R&R.
09-04-21, 11:08 PM
#1
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A question about bottom bracket R&R.
Hello All,
I'm slowly moving through cleaning, servicing, lubing, etc. on my '77 Motobecane Grand Jubile. It came to me in almost perfect shape and I don't want to screw anything up. I'm a novice and I'm buying tools as I need them, and watching videos. So far, I've done the front and rear axles and the freewheel (clean, replace bearings, re-lube). Now I'm on the bottom bracket. I've pulled the cranks (with the correct classic SR Sakai puller that I bought used from a bike repair guy who was closing his shop), and ordered a couple of Park Tools, the HCW-4 and HCW-5, in order to remove the fixed and adjustable cups, so no problems so far.
Here's my conundrum: I've seen a couple of videos of this operation and in one the mechanic says that that the square tapered spindle and the female crank opening should be cleaned of all lubricant when re-fitted or the crank may be drawn up too far on the spindle and crack at the corners. I have a problem with this theory. I've lived on boats for many years and I know that dis-similar metals tend to destroy one another in the absence of any lubricant/sealant, so I instinctively want to lightly grease the spindle contact surface. Also, I would think that there is a standard torque setting for the bolts that would correct this issue (although I haven't seen it yet).
Here's my question for the experts: Should I leave an aluminum/steel interface clean of all protection in the interest of friction or not?
Here's my second question: Does anyone know the torque setting for drawing up the crank arms to the spindle?
I know these might seem like small matters in today's world, but I'm taking the Hippocratic approach to this beautiful machine – First, do no harm.
Thanks,
Brian
I'm slowly moving through cleaning, servicing, lubing, etc. on my '77 Motobecane Grand Jubile. It came to me in almost perfect shape and I don't want to screw anything up. I'm a novice and I'm buying tools as I need them, and watching videos. So far, I've done the front and rear axles and the freewheel (clean, replace bearings, re-lube). Now I'm on the bottom bracket. I've pulled the cranks (with the correct classic SR Sakai puller that I bought used from a bike repair guy who was closing his shop), and ordered a couple of Park Tools, the HCW-4 and HCW-5, in order to remove the fixed and adjustable cups, so no problems so far.
Here's my conundrum: I've seen a couple of videos of this operation and in one the mechanic says that that the square tapered spindle and the female crank opening should be cleaned of all lubricant when re-fitted or the crank may be drawn up too far on the spindle and crack at the corners. I have a problem with this theory. I've lived on boats for many years and I know that dis-similar metals tend to destroy one another in the absence of any lubricant/sealant, so I instinctively want to lightly grease the spindle contact surface. Also, I would think that there is a standard torque setting for the bolts that would correct this issue (although I haven't seen it yet).
Here's my question for the experts: Should I leave an aluminum/steel interface clean of all protection in the interest of friction or not?
Here's my second question: Does anyone know the torque setting for drawing up the crank arms to the spindle?
I know these might seem like small matters in today's world, but I'm taking the Hippocratic approach to this beautiful machine – First, do no harm.
Thanks,
Brian
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09-04-21, 11:42 PM
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I will guess that most of us very, very very lightly lubricate the spindle taper with grease.
I don't use a torque wrench. I just know when to say when, which is hard to describe.
I don't use a torque wrench. I just know when to say when, which is hard to describe.
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09-05-21, 12:14 AM
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Hello All,
I'm slowly moving through cleaning, servicing, lubing, etc. on my '77 Motobecane Grand Jubile. It came to me in almost perfect shape and I don't want to screw anything up. I'm a novice and I'm buying tools as I need them, and watching videos. So far, I've done the front and rear axles and the freewheel (clean, replace bearings, re-lube). Now I'm on the bottom bracket. I've pulled the cranks (with the correct classic SR Sakai puller that I bought used from a bike repair guy who was closing his shop), and ordered a couple of Park Tools, the HCW-4 and HCW-5, in order to remove the fixed and adjustable cups, so no problems so far.
Here's my conundrum: I've seen a couple of videos of this operation and in one the mechanic says that that the square tapered spindle and the female crank opening should be cleaned of all lubricant when re-fitted or the crank may be drawn up too far on the spindle and crack at the corners. I have a problem with this theory. I've lived on boats for many years and I know that dis-similar metals tend to destroy one another in the absence of any lubricant/sealant, so I instinctively want to lightly grease the spindle contact surface. Also, I would think that there is a standard torque setting for the bolts that would correct this issue (although I haven't seen it yet).
Here's my question for the experts: Should I leave an aluminum/steel interface clean of all protection in the interest of friction or not?
Here's my second question: Does anyone know the torque setting for drawing up the crank arms to the spindle?
I know these might seem like small matters in today's world, but I'm taking the Hippocratic approach to this beautiful machine – First, do no harm.
Thanks,
Brian
I'm slowly moving through cleaning, servicing, lubing, etc. on my '77 Motobecane Grand Jubile. It came to me in almost perfect shape and I don't want to screw anything up. I'm a novice and I'm buying tools as I need them, and watching videos. So far, I've done the front and rear axles and the freewheel (clean, replace bearings, re-lube). Now I'm on the bottom bracket. I've pulled the cranks (with the correct classic SR Sakai puller that I bought used from a bike repair guy who was closing his shop), and ordered a couple of Park Tools, the HCW-4 and HCW-5, in order to remove the fixed and adjustable cups, so no problems so far.
Here's my conundrum: I've seen a couple of videos of this operation and in one the mechanic says that that the square tapered spindle and the female crank opening should be cleaned of all lubricant when re-fitted or the crank may be drawn up too far on the spindle and crack at the corners. I have a problem with this theory. I've lived on boats for many years and I know that dis-similar metals tend to destroy one another in the absence of any lubricant/sealant, so I instinctively want to lightly grease the spindle contact surface. Also, I would think that there is a standard torque setting for the bolts that would correct this issue (although I haven't seen it yet).
Here's my question for the experts: Should I leave an aluminum/steel interface clean of all protection in the interest of friction or not?
Here's my second question: Does anyone know the torque setting for drawing up the crank arms to the spindle?
I know these might seem like small matters in today's world, but I'm taking the Hippocratic approach to this beautiful machine – First, do no harm.
Thanks,
Brian
The boat analogy is apples and oranges, they suffer from electrolysis, hence the anodes and sacrificial plates used for that.
Most/all vintage cranks and axles now have been in service long enough and are sound enough that they rarely crack at the square taper hole, I've never seen one do so but I have seen a few that have stretched so the bolt bottoms out on the axle before it is tight enough.
The torque specs are easy enough to find but I suspect many here do it by feel with experience over many years of servicing.
The grease question is an age old conundrum and while I see many that seem to not have had any grease, it may not hurt.
On the other hand however I have often thought it possible that the grease may facilitate the stretching by helping the arm seat on further than it should.
The stiction of the interface may be the balance of tight enough without overtightening and stretching, maybe.
The really fun part is yet to come, removing the fixed cup if it is very tight can be one of the greatest cycling adventures you will encounter, many here will advocate for leaving it alone, cleaning as best you can from the other side.
I remove every single one for proper service and inspection, period.
09-05-21, 12:30 AM
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I’m in the “lightly grease the tapers” camp.
I use 30 ft-lbs for the crank arm bolts, and 40 ft-lbs for the DS of a sealed BB, confirmed as good middle of the range numbers for each location by Zinn’s manual. They’re the only places on a C&V bike where I use a torque wrench. I do use a small one on threadless stem bolts (typically @ 6 ft-lbs) of my wife’s modern-ish bike despite the steel steerer, since manufacturers seem picky about those bolts and they seem easy to over-tighten. I use Permatex silver anti-seize on all fastener threads, unless the component manufacturer has pre-applied blue Locktite.
BTW, on my own bikes, or those that I wrench upon frequently, I will re-torque those crank arm bolts to the same spec after about 50 miles. Then leave them alone!
I use 30 ft-lbs for the crank arm bolts, and 40 ft-lbs for the DS of a sealed BB, confirmed as good middle of the range numbers for each location by Zinn’s manual. They’re the only places on a C&V bike where I use a torque wrench. I do use a small one on threadless stem bolts (typically @ 6 ft-lbs) of my wife’s modern-ish bike despite the steel steerer, since manufacturers seem picky about those bolts and they seem easy to over-tighten. I use Permatex silver anti-seize on all fastener threads, unless the component manufacturer has pre-applied blue Locktite.
BTW, on my own bikes, or those that I wrench upon frequently, I will re-torque those crank arm bolts to the same spec after about 50 miles. Then leave them alone!
Last edited by Dfrost; 09-05-21 at 12:37 AM.
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09-05-21, 10:16 AM
#6
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I'm not sure how to interpret "very light" greasing, as in this case any lubricant at all will change the press fit value achieved with any given level of torque.
May as well grease it heavily, it should make no difference imo, but different formulations of lube introduce yet another variable that isn't a factor with a dry installation.
But dry installation requires more torque.
If there is a torque spec to be found for a particular set of crankarms, then the spec is valid only for the prescribed "dry" or "lubed" installation method that the torque spec is intended for.
Using LocTite on the crank bolt threads is one way to lessen any concerns of the bolt possibly loosening, without possibly over-torquing or repeat-tightening.
But in general, crank bolts should be tightened "pretty heavily". Often this is more than some people would expect, commonly it's around 30 ft-lbs!
May as well grease it heavily, it should make no difference imo, but different formulations of lube introduce yet another variable that isn't a factor with a dry installation.
But dry installation requires more torque.
If there is a torque spec to be found for a particular set of crankarms, then the spec is valid only for the prescribed "dry" or "lubed" installation method that the torque spec is intended for.
Using LocTite on the crank bolt threads is one way to lessen any concerns of the bolt possibly loosening, without possibly over-torquing or repeat-tightening.
But in general, crank bolts should be tightened "pretty heavily". Often this is more than some people would expect, commonly it's around 30 ft-lbs!
09-05-21, 10:42 AM
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There are folks out there who will emit blood curdling screams if you grease a Campy 10 speed square taper, but in general I think opinions are fairly evenly mixed. Me? I usually grease a little. As far as tightening the fixing bolt, I usually stop right before I want to say "oomph!"
If the BB was working fine, you don't necessarily need to remove the fixed cup. It can be overhauled in place. That being said I often remove it because I have a nice tool and it's one more thing for me to tinker on.
If the BB was working fine, you don't necessarily need to remove the fixed cup. It can be overhauled in place. That being said I often remove it because I have a nice tool and it's one more thing for me to tinker on.
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09-05-21, 11:08 AM
#8
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yes and no
I can see how drawing it up too far may cause them to crack but.... "too far would require some crazy amount of torque. I do not know the correct torque setting but I have overhauled hundreds of bikes new and old and never gave it a second thought about adding light grease to pretty much all metal on metal contact. Even without some lubricant I'm thinking one could find a way to over-tighten. Then again, I could have been doing it wrong all these years.
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09-05-21, 11:19 AM
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...this topic has engendered spirited discussion on bicycle forums ever since I started reading them, long ago.
I used to install them dry, and attempt to torque them to specs, then retorque after riding some miles.
Now, I grease lightly, and tighten them down as hard as I can with a Campy BB wrench, which by it's short handle arm, limits the torque you can apply. I've not noticed a difference.
Here's a link to the page discussion over on the Sheldon Brown website: https://www.sheldonbrown.com/brandt/...ng-cranks.html
A lot of the Jobst Brandt quotes come from his old discussion board , where there was a long back and forth on this. It's another example of bicycle mythology, like much of the chain lube discussion hereabouts.
You really ought to read the whole thing, over on the website, because it's interesting on this topic.
...this topic has engendered spirited discussion on bicycle forums ever since I started reading them, long ago.
I used to install them dry, and attempt to torque them to specs, then retorque after riding some miles.
Now, I grease lightly, and tighten them down as hard as I can with a Campy BB wrench, which by it's short handle arm, limits the torque you can apply. I've not noticed a difference.
Here's a link to the page discussion over on the Sheldon Brown website: https://www.sheldonbrown.com/brandt/...ng-cranks.html
A lot of the Jobst Brandt quotes come from his old discussion board , where there was a long back and forth on this. It's another example of bicycle mythology, like much of the chain lube discussion hereabouts.
Because friction plays no role in torque transmission, preload in the press fit must be great enough to prevent elastic separation between the crank and spindle under torque and bending. This means that no gap should open between crank and spindle facets under forceful pedaling. Crank bore failure occurs when the press fit is loose enough that a gap opens between spindle and crank. Torque is transmitted by both the leading and the trailing half of each facet, contact pressure increasing and decreasing respectively. In the event of lift-off, the entire force bears only on the leading edge of facets and causes plastic deformation, causing the bore to take on a "pincushion" shape (loose crank syndrome). Subsequent tightening of the retaining screw cannot correct this because neither the retaining bolt nor crank is strong enough to re-establish the square bore.
The claim that a greased spindle will enlarge the bore of a crank and ultimately reduce chainwheel clearance is also specious, because the crank cannot operate in a plastic stress level that would soon split the crank in use. However, increased engagement depth (hole enlargement) may occur without lubricant, because installation friction could ream the hole.
With or without lubricant, in use, cranks will make metal-to-metal contact with the spindle, causing fretting erosion of the steel spindle for all but the lightest riders. Lubricating the spindle for assembly assures a predictable press fit for a given torque. Without lubrication, the press is unknown, and galling (aluminum transfer to the steel spindle) may occur during assembly. After substantial use, spindle facets may show rouge and erosion from aluminum oxide from the crank, showing that lubricant was displaced.
The claim that a greased spindle will enlarge the bore of a crank and ultimately reduce chainwheel clearance is also specious, because the crank cannot operate in a plastic stress level that would soon split the crank in use. However, increased engagement depth (hole enlargement) may occur without lubricant, because installation friction could ream the hole.
With or without lubricant, in use, cranks will make metal-to-metal contact with the spindle, causing fretting erosion of the steel spindle for all but the lightest riders. Lubricating the spindle for assembly assures a predictable press fit for a given torque. Without lubrication, the press is unknown, and galling (aluminum transfer to the steel spindle) may occur during assembly. After substantial use, spindle facets may show rouge and erosion from aluminum oxide from the crank, showing that lubricant was displaced.
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09-05-21, 11:35 AM
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Hello All,
I'm slowly moving through cleaning, servicing, lubing, etc. on my '77 Motobecane Grand Jubile. It came to me in almost perfect shape and I don't want to screw anything up. I'm a novice and I'm buying tools as I need them, and watching videos. So far, I've done the front and rear axles and the freewheel (clean, replace bearings, re-lube). Now I'm on the bottom bracket. I've pulled the cranks (with the correct classic SR Sakai puller that I bought used from a bike repair guy who was closing his shop), and ordered a couple of Park Tools, the HCW-4 and HCW-5, in order to remove the fixed and adjustable cups, so no problems so far.
Here's my conundrum: I've seen a couple of videos of this operation and in one the mechanic says that that the square tapered spindle and the female crank opening should be cleaned of all lubricant when re-fitted or the crank may be drawn up too far on the spindle and crack at the corners. I have a problem with this theory. I've lived on boats for many years and I know that dis-similar metals tend to destroy one another in the absence of any lubricant/sealant, so I instinctively want to lightly grease the spindle contact surface. Also, I would think that there is a standard torque setting for the bolts that would correct this issue (although I haven't seen it yet).
Here's my question for the experts: Should I leave an aluminum/steel interface clean of all protection in the interest of friction or not?
Here's my second question: Does anyone know the torque setting for drawing up the crank arms to the spindle?
I know these might seem like small matters in today's world, but I'm taking the Hippocratic approach to this beautiful machine – First, do no harm.
Thanks,
Brian
I'm slowly moving through cleaning, servicing, lubing, etc. on my '77 Motobecane Grand Jubile. It came to me in almost perfect shape and I don't want to screw anything up. I'm a novice and I'm buying tools as I need them, and watching videos. So far, I've done the front and rear axles and the freewheel (clean, replace bearings, re-lube). Now I'm on the bottom bracket. I've pulled the cranks (with the correct classic SR Sakai puller that I bought used from a bike repair guy who was closing his shop), and ordered a couple of Park Tools, the HCW-4 and HCW-5, in order to remove the fixed and adjustable cups, so no problems so far.
Here's my conundrum: I've seen a couple of videos of this operation and in one the mechanic says that that the square tapered spindle and the female crank opening should be cleaned of all lubricant when re-fitted or the crank may be drawn up too far on the spindle and crack at the corners. I have a problem with this theory. I've lived on boats for many years and I know that dis-similar metals tend to destroy one another in the absence of any lubricant/sealant, so I instinctively want to lightly grease the spindle contact surface. Also, I would think that there is a standard torque setting for the bolts that would correct this issue (although I haven't seen it yet).
Here's my question for the experts: Should I leave an aluminum/steel interface clean of all protection in the interest of friction or not?
Here's my second question: Does anyone know the torque setting for drawing up the crank arms to the spindle?
I know these might seem like small matters in today's world, but I'm taking the Hippocratic approach to this beautiful machine – First, do no harm.
Thanks,
Brian
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09-05-21, 12:59 PM
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Thanks for the great info everyone!
"Correct" is what the manufacturer tells you to do. If Brand C tells you to clean and degrease the parts, then use a peanut butter wrench to install the cranks, do that. If Brand R tells you to use grease and a peanut butter wrench, do that. Most of my stuff is Brand S who provides a torque spec and ships bottom brackets with a light greasy coating on the bottom bracket tapers but no instructions to degrease them, so I don't.
I went all over the web before I asked this question of the group. I've downloaded probably about a dozen vintage Motobecane catalogs and a couple of owner's manuals. Actually, you'd think that there would be a few shop manuals floating around out there but I couldn't find any. The closest thing to manufacturer's instructions I can find is, "The crank assembly should be cleaned, inspected and lubricated by your Motobecane Dealer every 1000 miles, assuming average conditions". Great for drumming up business for the dealers, but not very informative for the owner.
Thanks for your info!
09-05-21, 01:20 PM
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Hi Scott,
I went all over the web before I asked this question of the group. I've downloaded probably about a dozen vintage Motobecane catalogs and a couple of owner's manuals. Actually, you'd think that there would be a few shop manuals floating around out there but I couldn't find any. The closest thing to manufacturer's instructions I can find is, "The crank assembly should be cleaned, inspected and lubricated by your Motobecane Dealer every 1000 miles, assuming average conditions". Great for drumming up business for the dealers, but not very informative for the owner.
Thanks for your info!
I went all over the web before I asked this question of the group. I've downloaded probably about a dozen vintage Motobecane catalogs and a couple of owner's manuals. Actually, you'd think that there would be a few shop manuals floating around out there but I couldn't find any. The closest thing to manufacturer's instructions I can find is, "The crank assembly should be cleaned, inspected and lubricated by your Motobecane Dealer every 1000 miles, assuming average conditions". Great for drumming up business for the dealers, but not very informative for the owner.
Thanks for your info!
When I don't know about a particular crank, I tend to "shoot for the middle" -- I'll use a light coating of oil on the spindle and torque to 25 ft-lbs, then see if it stays put after some riding. When re-checking the torque, I use a beam-type wrench that lets me see the torque level where I start meeting resistance. If it resists right away and indicates about 10-15 ft-lbs, then I figure the crank is seated pretty well, and I might only pull up to 20 ft-lbs or so. If the bolt hardly resists at all, then I might pull it all the way back up to 25 ft-lbs and make a note to check it again soon. It should stabilize and not need any more attention after that; higher torque may be needed if it doesn't.
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09-05-21, 04:42 PM
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Death fork? Naaaah!!
FWIW, I assemble crank sets dry.
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09-05-21, 04:53 PM
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Sounds like you've done your due diligence, then! I honor that and your "first do no harm" attitude.
When I don't know about a particular crank, I tend to "shoot for the middle" -- I'll use a light coating of oil on the spindle and torque to 25 ft-lbs, then see if it stays put after some riding. When re-checking the torque, I use a beam-type wrench that lets me see the torque level where I start meeting resistance. If it resists right away and indicates about 10-15 ft-lbs, then I figure the crank is seated pretty well, and I might only pull up to 20 ft-lbs or so. If the bolt hardly resists at all, then I might pull it all the way back up to 25 ft-lbs and make a note to check it again soon. It should stabilize and not need any more attention after that; higher torque may be needed if it doesn't.
When I don't know about a particular crank, I tend to "shoot for the middle" -- I'll use a light coating of oil on the spindle and torque to 25 ft-lbs, then see if it stays put after some riding. When re-checking the torque, I use a beam-type wrench that lets me see the torque level where I start meeting resistance. If it resists right away and indicates about 10-15 ft-lbs, then I figure the crank is seated pretty well, and I might only pull up to 20 ft-lbs or so. If the bolt hardly resists at all, then I might pull it all the way back up to 25 ft-lbs and make a note to check it again soon. It should stabilize and not need any more attention after that; higher torque may be needed if it doesn't.
09-06-21, 05:46 AM
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I'm not convinced that many of the "dry taper" are actually degreasing the metal surfaces before assembly. Interference fits have a "less than zero" tolerance, any extra lubricant needs to hydraulic out of the joint, and I'm going to make a guess here, but the energy/torque needed to move the grease out adds a variable to the creation of an interference fit that relies on "stiction" Myself I make sure to wipe all the grease off the spindle before assembly, and will lightly grease and wipe clean a spindle that has been degreased.
Only data point I can realy add is that I while trying to free something up I got Triflow on the the left spindle of my assemble bike and then went for a ride. The left crank arm worked loose with in a couple miles. It had been a while since I had checked the bolts, but it had held fine with just the stiction.
Only data point I can realy add is that I while trying to free something up I got Triflow on the the left spindle of my assemble bike and then went for a ride. The left crank arm worked loose with in a couple miles. It had been a while since I had checked the bolts, but it had held fine with just the stiction.
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09-06-21, 11:20 AM
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Slap on a thin coat of anti-seize then wipe it off. It gives me reassurance that I will be able to get it off without damage latter. I use a torque wrench when tightening down my cranks. Its not that I could not do without it but it gives me reassurance that the crank is in fact installed correctly. Also, there is not a need to buy a special torque wrench.
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No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)
No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)
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09-06-21, 08:25 PM
#20
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