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Does Octalink can loosen by itself?

Old 02-05-19, 03:28 AM
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bartek. 
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Does Octalink can loosen by itself?

Hi guys,

I'm pretty sure there are many experts of Octalink system here that could give me a hint regarding my issue.
I've been using Dura-Ace BB-7710 with my SRM Track for over a year now. After about 1000km I started to hear occasional creaking under my legs during accelerations (AFAIR standing and seated) with high power (1000W+). Occasional means it was about 5 creaks in total maybe (I'm endurance, not sprinting that much) for 2 training sessions or so. I verified it my hand and while pushing crank arms by hands (obviously by using a lot of body weight) I could hear the creak, so I decided to tighten the crank arm (I'm referring here to the 8mm allen wrench) as I haven't done it since I built the bike 1000km ago. It turned out I needed about a full turn to get torque of 40Nm (SRM specs says 40-50Nm). After that I rode another 500km including few races and some massive acceleration workouts on 58x12 - no problem at all.

Well, few days ago I was doing a standing acceleration (1200W) on a low gear (52x16) and again, I heard the creak! Rechecked with a torque wrench, I could turn maybe about 1/4 on one arm and 1/3 on another to receive desired torque values this time - basically not much, but still.

I am not a mechanic and I am not really into this kind of engineering, so I did a research on the Internet and I read that Octalink basically should never loosen by itself, once it was mounted correctly. Also, most of the problems with creaking crankarms mounted on octalinks turned out to be an actual problem with the octalink bottom bracket itself and it should be remounted (with cleaning and regreasing). As the SRM is pretty expensive and I don't really want to break it, I went to my LBS that actually assembled the bike and components and I asked for a help.

The LBS claimed this cannot be a bottom bracket issue and they refused to remounted it or even retighten. They claimed this as a normal situation, especially on track as track riders generate more power and there is more forces on velodrome than any other place and there is a chance a crankarm can be loosen from time to time. They unscrewed the crank bolt self extract (I believe this is a correct English name - I am referring to this parts: https://www.bicyclehero.com/us/p-s-p...f-extract.html), put a blue loctite on the threads and tighten the bolts again.

Is it possible that the crankarms on octalink can loosen from time to time? After 500km? That would mean some elite riders would need to recheck the bolt every single session I guess as I am a small guy compared to the big guys. This is not a square taper and it does not make sense to me what they were saying. I cannot remember even one loosen on my other track bike with Sugino 75 (square taper!) that I was riding for years (also on street). In fact, I am scared if the crankarm arm interface is not smashed now or something. I know this can happen on square taper crankset. Shall I remount/tighten the bottom bracket? Or maybe this time the creak could come from a pedal this time? Unfortunately I haven't verified by hand this time but I had my pedals demounted after flying from a competition, so there is a chance I didn't tighten pedals enough (which actually never happened before!).

There is also another thing. I'm attaching a picture of my right crankarm. As you can see the self extract bolt does not fit nice into the crankarm. It looks weird but threads are fine for sure and basically it looks like the hole was made not super precisely but threads are fine. I was told this is not an issue as this bolt doesn't matter much and I shouldn't even send it to SRM under warranty as this is cosmetic. Is it? The last creak I would say was from the right side (this is actually why I also thought about pedals as I definitely felt it more under my right foot).

What do you think about it? I am a bit worried that something is really wrong and it's going to cost money, I'm not sure who is responsible for it ;/


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Old 02-05-19, 03:44 AM
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I might re-check the crank bolts once after you start riding, but not repeatedly.

If the face of the crank is curved, then a portion of the extractor might stick out.

However, your crank appears to have a face that is flat (perpendicular to the bottom bracket spindle. So, I'd expect the extractor to be flush.

If that crank face is actually perpendicular to the bottom bracket, then that extractor is not normal, and trying to use it could cause binding and/or stripping of the threads. I'm surprised the threads are "OK" as it looks cross-threaded.

I'd talk to your manufacturer, especially as that looks like a very expensive crankset.
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Old 02-05-19, 04:16 AM
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Indeed, the crank face is flat. On the left side the extractor is fully inside the crank hole and perpendicular to the crank arm and bottom bracket spindle).

Once the LBS wanted to unscrew it they were also surprised how it looked like and thought that the thread was cross-threaded. It was a bit harder to unscrew from this side too but once unscrewed we verified the threads on the extractor and it looked really OK, also it was very easy to tighten it back. So they said as it looked like the hole in the crank was drilled not super precisely but at the end it's not an issue as threads are fine and should not have any impact on how the cranks work.
As you said, this is very expensive stuff and I have to consider that maybe they just tried to hide they mistakes when they mounted it in first place.
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Old 02-05-19, 04:27 AM
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The problem is when you try to unscrew the crank bolt, it will hit the "extractor" unevenly, and could cause the threads to pop.

If you remove the "extractor", and use a normal crank remover, either it will go in crooked, or the threads will be stripped, and it won't work properly.

I have troubles imagining a company could do precision machining, and get the threads crooked. But, they could potentially have forced a cross-threaded part in at the factory.

I have a lot of tolerance, but that one would bother me for the next time you have to do maintenance on the crankset or bottom bracket. Or the second or third maintenance cycle.
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Old 02-05-19, 04:50 AM
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extractor cap is definitely not on correctly.

Check the splines of the bb and the matching splines in the crankarms, look for any rounding/damage.

In general an octalink crank should not loosen overly... but slightly working it's way back (what you describe) wouldn't immediately raise alarm bells in my mind. If there is not damage to the interface between bb/crank, then your problem is either the bb having play (check this with the crank off by trying to forcibly move the axle back/forth up/down while it's installed properly in the bike) or your extractor bolt interfering with the crank and not allowing it to properly thread onto the bb splines.

*i do think the extractor bolt is not on correctly, but i doubt it's keeping it from bolting on... if it were you definitely wouldn't have made it 500k without knowing.
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Old 02-06-19, 07:49 AM
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I own 2 track SRM's and on both the extractor bolts sit flush.

I have had the crank arms loosen a couple of times over the years. I just regreased the bolts and retightened to the correct torque. No issues with the interface.
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Old 02-07-19, 05:23 PM
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I came across a little mention on this issue and it stuck in my head as I was having a similar issue many years ago. Basically the DA cranks that came on my first track bike about 11yrs ago never loosened. Then I decided to go to 175 cranks and got new DA cranks and they were constantly coming loose such that I had to tighten about every 2 weeks or about 6 training and racing sessions. I came across a snippet from someone that said that newer bolts were ever so slightly different in dimension to older ones. So I still had the old cranks and bolts so I re-used the old bolts and never had a problem since. Until going to Vision cranks in November I was still using those original bolts and zero issues. Now I don't know just how correct that info I found was, but when I went back to the older bolts and zero issues it was enough for me to say there's definitely something there. A dab of blue locktite might do the fix for you
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Old 02-08-19, 06:19 PM
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The extractor bolts in the SRM arms are not Dura ace. I had the SRM provided bolts loosen a few times, but this was before I bought the second unit so I didn't have to be constantly swapping it between bikes (I had a spare non-driveside arm on the other bike therefore was only swapping out the SRM).

Just grease the bolt threads, torque and check every now and then.

Only thing I'd be concerned with is how the extractor bolt is sitting...
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Old 02-12-19, 10:56 AM
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After first comments I realised that I should get a knowledge base about what we are talking about to not to mess up with your valuable informations. So, here I am back

First of all, I presented 2 issues separately in my original post (the creaking crankset, the extract bolt not sitting properly). So, some comments were regarding one thing, some regarding another. I understand that there can be many independent circumstances, however after some research, I've been coming to think this both issues might be connected.

I highly doubt that manufacturer could crooked threads. I also doubt that a mechanic could tighten bolt while installing in a wrong manner and didn't say a single word. I believe I would notice it immediately and ask questions. I also need to add that once the issue was discovered it wasn't that super easy to unscrew the extractor bolt compared to the left arm. The bolt was slightly roasted. This gives me thinking that some unexpected forces were in the game.

So, what about this 2 articles I found as references in some Octalink issue related questions?
https://www.sheldonbrown.com/brandt/...ng-cranks.html
https://www.sheldonbrown.com/brandt/...ng-cranks.html

This crank attachment was apparently designed assuming that all riders lead with the left foot when standing on both pedals, typically over rough terrain. Properly tightened retaining bolts can loosen only with weight on both pedals, right foot forward, because this is the only condition under which the crank spindle torque reverses.
The left crank transmits driving torque through the spindle to the right crank and chainwheel while the right crank drives the chainwheel directly. Besides that, the right crank transmits torque to the spindle only when standing on both pedals. Doing this with the right foot forward (goofy footed) is the only time the spindle transmits reverse torque.
And more in these 2 articles. I must admit that I remember creaking from the right side (under right foot) and only while starting a massive sprint. This could mean I start the sprints in similar conditions to "standing start with right foot forward". And yes, I am goofy footed. So what about if this makes the crank spindle torque reverses and as the crank bolt unscrews with massive reverse torque it loosens (this makes creaks later) and hits the extractor bolt. As the crank arm threads are softer than extractor bolt this finishes with crooked threads in the crank arm and extractor bolt not sited perpendicular to the bottom bracket. Does it make any sense? Or I'm overthinking?
I only inspected threads on the extractor bolt (they were OK), haven't verified threads on the crank arm that could be crooked.

So, this is what I think should be done now:
- Unscrew the extractor bolt, verify threads both on the bolt and in the crank arm. I could try to tighten another bolt to see how it sits, or use a calliper. Basically, I need to find a source of not properly sited extractor bolt.
- Put the extractor bolt back into position, and try to take the crank arms off. This can be tricky as it may damage the extractor threads that @CliffordK referred to.
- Verify connector condition for roundness and strips.
- Check if spindle has no loosen in any directions. If so, remount bottom bracket.
- Remove seals from bearings to spin more smoothly
- Regrease spindle and rotate it to not match the same connectors from the crank arm (just in case some are rounded or so)
- Replace the alu crank bolt for steel crank bolt
- Tight more than alu crank bolt. Alu crank bolt torque is 40-50Nm recommended, so I guess 60Nm would be fine for steel bolt.
- How to fix the probably crooked threads for the extractor bolt? And maybe replace alu one with a steel version if anywhere available?

What do you think guys? Does it make sense? I am not experienced with engineering, so maybe there are better options? Who is responsible for eventual damage?
I also verified some videos of 1 kilo starts of elite riders and definitely I wouldn't say nobody starts from the right foot. 50/50 which makes sense as some are regular, some goofy..

Originally Posted by Dalai
I have had the crank arms loosen a couple of times over the years. I just regreased the bolts and retightened to the correct torque. No issues with the interface.
Have you experienced creaks when arms were loosen? BTW. I never felt like crank arm was loosen or wanted to fall off, just creaks mainly.

Originally Posted by brawlo
I came across a snippet from someone that said that newer bolts were ever so slightly different in dimension to older ones. So I still had the old cranks and bolts so I re-used the old bolts and never had a problem since. Until going to Vision cranks in November I was still using those original bolts and zero issues. Now I don't know just how correct that info I found was, but when I went back to the older bolts and zero issues it was enough for me to say there's definitely something there.
As @Dalai already answered this are SRM bolts, not DA. However, as long as I can imagine that your newer bolts came slightly different (like a bit shorter thread) I don't think this could be a rule of thumb. There could be some individual cases but nothing that could be in production line for years. I am pretty sure Shimano would noticed an issue with wrong bolts shorter or later. However, my optimism could be too high :-)
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Old 02-12-19, 12:01 PM
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Thanks,
I never thought about right or left foot forward.

I don't think it applies to starting off... I unclip with left, and start riding with right foot at 1:00 or 2:00.

But, rather if you are say standing on the pedals without pedaling such as going over bumps or around corners.

Putting weight on the left crank with the crank back will reverse the direction on the crank around the spindle (clockwise looking from the left side)

Left foot forward, weight on right crank puts the same stress on the joint as you would get from pedaling (counterclockwise from the left side)

One doesn't get the same reverse torque if both feet are generally moving forward.

I am a little surprised that anybody is actually making Octalink V1 cranks. I know there are a lot of 6500 and 7700 cranks out there, so cross compatibility is nice, but I'd expect the choice to go with either Octalink V2 or ISIS.
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Old 02-12-19, 12:17 PM
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Not sure if you are aware of this or not but the ďoctalinkĒ axle spline pattern is not symmetrical all the way around. There is one spline that is thinner (or maybe thicker, I would have to go look). This is important because it references the drive and non-drive arms at 180 degrees from one another. The incorrect spline engagement looks a lot like the correct spline engagement which makes for a strong possibility that incorrect installation could go ubdetected. Tightening down a crank arm that is out of position is possible but because it is not fully seated on the splines tab, it can shift later while under load.

Now i I have not worked with the track Octalink but I believe it should be the same concept as the road Octalink. The one I have is the Ultegra 6503 triple.

Now I cannot say for sure if what happened to me happened to you but it sure sounds like it. The way I positively resolved my issue and restored full confidence in the strength and reliability of the system is as follows: 1) make sure the interior threads of the hollow axle are lightly greased 2) do not use a standard 8mm Allen wrench, it is one sided and has the problem of not providing enough tactile feedback and does not apply tightening torque evenly. Instead I highly recommend a sliding ďTĒ bar that takes an 8mm Allen bit. I like 3/8 drive since it is a bit stronger than 1/4 but leads massive than the 1/2 square drive Allen socket. So long as you have you auto extract bolt fully tightened into your crank arm you can then line up the mating splines, taking care that it is on the correct axle locating pin. Start tightening the T-bar with the 8mm bit and you should be able to feel if there is any resistance. If there is you can always back it out, check everything and try again. Once you are locked on where you need to be, youíll feel that the splines are snuggling up properly. The greased axle threads help with this feel. Applying equal hand pressure on both ends of the T bar, tighten the auto extracting bolt quite tight and it will stop at some point when it is very tight so donít force it beyond that point.

when done this way, you will know without question that it is installed correctly. I feel that the Octalink USA very elegant, strong setup that gets bad press at times for what is really a mechanic issue. Loctite is not necessary or appropriate here in my opinion.

if it would make you feel better, you could also use crank bolts of the correct size and forget about the auto extractor bolts. Some of the XTR Octalink cranks connected this way Ithink.

As for whether a slight asymmetric projection of the auto extract collar is a problem - I would say donít worry about it so long as the threaded collar that holds the crank bolt is not cross threaded.

Iím curious to know if my advice is helpful or applies to your situation at all.
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Old 02-12-19, 12:29 PM
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Originally Posted by CliffordK View Post
I never thought about right or left foot forward.
I don't think it applies to starting off... I unclip with left, and start riding with right foot at 1:00 or 2:00.
Well, I am 100% goofy for sure. I had been doing skateboarding for years I my right leg is leading. However I unclip with both occasionally. I don't mean only standing starts as creaking was while simple but usually connected to standing in pedals for better acceleration. I have never thought about it but it's possible that I always start sprinting from the right foot forward. I can be simple natural. Even if I start at 1 or 2 o'clock that doesn't mean there can't be some reverse few moments later when at 12 that actually could makes creaks.

Originally Posted by CliffordK View Post
But, rather if you are say standing on the pedals without pedaling such as going over bumps or around corners.
Well, I guess you are more experienced than me here.

Originally Posted by CliffordK View Post
Putting weight on the left crank with the crank back will reverse the direction on the crank around the spindle (clockwise looking from the left side)
Left foot forward, weight on right crank puts the same stress on the joint as you would get from pedaling (counterclockwise from the left side)
One doesn't get the same reverse torque if both feet are generally moving forward.
I'm not sure if I understand your meaning here. I talked about putting weight on the right crank forward and pull the light crank. I feel lost now :-)

Originally Posted by CliffordK View Post
I am a little surprised that anybody is actually making Octalink V1 cranks. I know there are a lot of 6500 and 7700 cranks out there, so cross compatibility is nice, but I'd expect the choice to go with either Octalink V2 or ISIS.
What can I say, as 7710 and 7700 are still very popular crank arms, SRM decided to go the same way and use Octalink V1 cranks. As this is one of the most favourite standard in elite riders I was pretty sure it's super strong and reliable. I guess it would be good to ask some elite sprinters if they do any modifications to the standard set ;-)
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Old 02-12-19, 12:39 PM
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Originally Posted by masi61 View Post
Not sure if you are aware of this or not but the “octalink” axle spline pattern is not symmetrical all the way around. There is one spline that is thinner (or maybe thicker, I would have to go look). This is important because it references the drive and non-drive arms at 180 degrees from one another. The incorrect spline engagement looks a lot like the correct spline engagement which makes for a strong possibility that incorrect installation could go ubdetected. Tightening down a crank arm that is out of position is possible but because it is not fully seated on the splines tab, it can shift later while under load.


OK, this is another aspect that should be investigated. So, I cannot rotate spline to change position of slots between spline and crank arm? They are always in the same position? I already heard that it's quite easy to mount crank arms in incorrect position but that would lead in not parallel crank arms and would be visible at first glance. I believe I would notice it after 5 minutes of rides.

Originally Posted by masi61 View Post
I’m curious to know if my advice is helpful or applies to your situation at all.
Originally Posted by masi61 View Post
Thanks for the advices! I really appreciate. I will try to get the T-bar tool for tightening. However at the end I may use a torque wrench to make the last turn. I may also take a look for a crank bolt without auto extractor (you mean 1 piece bolt right?). I guess in steel would suits perfectly and safe.
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Old 02-12-19, 01:19 PM
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I haven't seen any indication of indexing of octalink V1, V2, or ISIS. If it is there, it is mighty subtle. Perhaps I'll have to try measuring one with calipers.

there was something that I ran into that was indexed like that. Car steering couplings are often indexed (but not necessarily steering wheels). I think some of the through-axle designs also have a similar indexing.

As far as the foot forward thing.

Right crank connected to chain. Bottom bracket just stabilizes it. Pedal back with right only, and it freewheels (or tensions chain on a fixie). Pedal forward, and torque taken up by the chain.

When pedaling forward with the left crank, it causes a counter clockwise rotation (from left side) at the left crank to bottom bracket, and then through the bottom bracket, and again at the right crank to bottom bracket interface.

Back pedalling with the left crank, and one gets a clockwise rotation on the bottom bracket/left crank, and at the the bottom bracket/right crank interfaces. That is probably OK if you are freewheeling, but would tend to twist the bottom bracket in relation to the cranks if braking (fixie/pedal brakes), or standing on the pedals with the left back.

Say you achieve 0.01į rotation at the crank/spindle location, then repeatedly hitting that +/- rotation could tend to wear the aluminum crank interface.

If this is an issue, then I'm surprised to hear that the Octalink is being used with fixies.

Square taper wouldn't be vulnerable to this as it is a press-fit (unless hollowed out).

The new through-axle (24/30mm) crank designs would also be less susceptible due to tightening down bolts for Shimano style cranks, and the triangular interface for Campy style cranks.
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Old 02-12-19, 02:24 PM
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Originally Posted by bartek. View Post
OK, this is another aspect that should be investigated. So, I cannot rotate spline to change position of slots between spline and crank arm? They are always in the same position? I already heard that it's quite easy to mount crank arms in incorrect position but that would lead in not parallel crank arms and would be visible at first glance. I believe I would notice it after 5 minutes of rides.



Thanks for the advices! I really appreciate. I will try to get the T-bar tool for tightening. However at the end I may use a torque wrench to make the last turn. I may also take a look for a crank bolt without auto extractor (you mean 1 piece bolt right?). I guess in steel would suits perfectly and safe.
Yes, by all means do your final tightening with a torque wrench but the preliminary & progressive tightening with the T-bar are highly recommended since you can FEEL if youíve got it right or not.

Yes, I mean a 1 piece bolt as an alternative to an auto extractor.

Octalinks for the road (V2?) are most definitely splined in a specific way. It is easy to overlook this fact. I mean if you got it really off then they would not be 180 degrees apart and you would most definitely feel that asymmetry. But it is also possible to erroneously install the drive side wrong, tighten it up wrong, then put the non drive side where you think it should be then tighten it up wrong as well. Iím at work now - when I get home Iíll post a photo demonstrating that what Iím talking about is a real thing.
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Old 02-12-19, 02:35 PM
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Originally Posted by bartek. View Post
Tight more than alu crank bolt. Alu crank bolt torque is 40-50Nm recommended, so I guess 60Nm would be fine for steel bolt.

Have you experienced creaks when arms were loosen? BTW. I never felt like crank arm was loosen or wanted to fall off, just creaks mainly.
SRM provides recommended torque values. This is for both the crank bolts and chainring bolts. Using different torque (especially the chainring bolts) will affect the accuracy and consistency of the power values. I always use a small torque wrench when changing rings and larger torque wrench for the crank bolts. It​​​ did creak a few times early on.
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Old 02-13-19, 05:12 AM
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Originally Posted by masi61 View Post


Yes, by all means do your final tightening with a torque wrench but the preliminary & progressive tightening with the T-bar are highly recommended since you can FEEL if youíve got it right or not.

Yes, I mean a 1 piece bolt as an alternative to an auto extractor.

Octalinks for the road (V2?) are most definitely splined in a specific way. It is easy to overlook this fact. I mean if you got it really off then they would not be 180 degrees apart and you would most definitely feel that asymmetry. But it is also possible to erroneously install the drive side wrong, tighten it up wrong, then put the non drive side where you think it should be then tighten it up wrong as well. Iím at work now - when I get home Iíll post a photo demonstrating that what Iím talking about is a real thing.
this seems to happen quite a bit more than you'd think.
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Old 02-13-19, 05:27 AM
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Originally Posted by Morelock View Post
this seems to happen quite a bit more than you'd think.
I may have to eat my words about the splines being indexed for one position only.... last night I checked a Dura Ace 7700 NOS bottom bracket that I had purchased for a retro road build - and I could not see any difference in the splines, they appeared all the same thickness.

This is odd odd though because I was fairly certain that the 7703 one that I used on my Ultegra 6503 triple crank wanted to be installed only one particular way. I will research this further and report back.
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Old 02-13-19, 06:58 AM
  #19  
Morelock
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^I don't believe they are splined for only one position, but it's entirely possible to thread the drive side on "tight'ish" without fully engaging. If that happens, you cannot get the nds arm to thread on and line up and tighten. I had a friend do this, took me a good few minutes to figure out what he had done.
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Old 02-13-19, 07:48 AM
  #20  
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You had me a bit worried about the splined for one position, because Iím pretty sure I just stuck mine on. Iím glad to hear others report that may not be the case.
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Old 02-13-19, 09:44 PM
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I've never seen this different spline position. Maybe it's being mistaken for free hub splines?
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Old 03-22-19, 11:39 AM
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I am back to this.
I unscrewed the extractor bolt and verified that all threads look mint. I noticed that on the crankarm there is full 4 threads and part of the 5th only when on the left arm there are full 5 threads. Interesting that the finishing thread is still black anodized.
Seems like the right extractor should be simply shorter and maybe I got 2 left arm extractor bolts by mistake. I talked to SRM Customer Service and they verified both extractor bolts are identical. They also confirm that on the right side the extractor shouldn't be fully flushed and basically everything is ok. They even sent me pictures of another crankset with the same situation.
So, is anyone can confirm that a right extractor bolt should be fully flushed? I'm talking here about the Track Science model where the spider is fully connected with the right crankarm. I know a previous version a spider and crankarm were separated.

The Octalink interface looks solid and in mint condition. It's possible to insert a printer paper between spindle and crankarm. However it's a maximum and it's exactly the same on both sides and very constant on all parts. I think this is correct. The position of the spindle also is correct.
I haven't extract the crankarm yet. I waited for a confirmation from the SRM that everything is OK and it's safe to do this. I will extract the crankarm and bottom-bracket, clean, regrease and mount back. We will see.
I'm just not sure if I should go with a grease or blue loctite on a crank bolt. I assume greasing should be all I need. The correct tighten value is 40-50Nm.





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