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First gen fluted Dura Ace cranks

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First gen fluted Dura Ace cranks

Old 02-23-19, 10:50 PM
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HM70
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First gen fluted Dura Ace cranks

The dura ace cranks are too far out on the bottom bracket of this used early Bottechia I just bought. Doesn't line up properly with the Dura ace 6 spd freewheel hub. Would my old campy or stronglight cranks fit?. Or would it be better to replace the BB (but what BB would work)?
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Old 02-23-19, 10:53 PM
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What is your spindle length? JIS of ISO square taper?

Should be 112/113 spindle with ISO taper.

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Old 02-23-19, 11:54 PM
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What I would do is search the website Velobase for your specific cranks. Each listing will have a spec for what length BB spindle you need for that crank to achieve a standard chainline.

For example, here is the listing for the 1st gen Dura Ace cranks: VeloBase.com - Component: Shimano GA-200, Dura-Ace First Gen

It recommends a 112 or 113mm BB spindle. So see if your current BB spindle is that length and if it's not, try a new BB that has a 112mm or 113mm spindle.
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Old 02-24-19, 02:48 PM
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Thanks! I looked up the Stronglight 105bis in Velobase and it has a longer BB length 118mm. We'll see if it fits. Gotta get a puller for the Dura ace first.
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Old 02-24-19, 02:55 PM
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Originally Posted by HM70 View Post
Thanks! I looked up the Stronglight 105bis in Velobase and it has a longer BB length 118mm. We'll see if it fits. Gotta get a puller for the Dura ace first.
You should look up the ISO and JIS standards for spindles and cranks before going any further. That info will save you some headaches in the future.
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Old 02-25-19, 11:41 AM
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what year Bottechia? What was original equipment? was it campy? what is the current bb make and lenght? you probably need take the BB out and look at it

also this has a lot if info https://www.sheldonbrown.com/bbtaper.html

you need to look up your exact crank model and BB apparently per sheldon Some older Shimano Dura Ace used a shorter taper than most other cranks.

so you need details, not just trying parts
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Old 02-25-19, 12:23 PM
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It can't hurt to test-fit the Stronglight crankset on the old spindle, and I suspect that will move your chainline inward several millimeters.

I often have found a too-long chainline dimension to be one of the most-annoying things about a bike, and I am not averse to using shorter-than-specified bottom bracket spindle lengths.
Indeed, one of the things that I despise about modern upscale road bikes is that there are no options to modify the chainline dimension other than to replace the crankset with something lower-end or much older and square taper.

Chainline dimension has historically been longer than optimal in many cases because of the possibility of the chain contacting and snagging the big ring's teeth when/if the rider used the bike with the chain crossed over between the smallest front and rear sprockets, but usually that is only a novice problem that doesn't exist for experienced riders unless their rear derailer cable were to fail.

So I usually try for the minimum spindle length that will still allow the front derailer to downshift with authority and that gives at least a full millimeter or so between a trued small chainring and the chainstay.
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Old 02-25-19, 08:55 PM
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Originally Posted by dddd View Post
I often have found a too-long chainline dimension to be one of the most-annoying things about a bike, and I am not averse to using shorter-than-specified bottom bracket spindle lengths.

So I usually try for the minimum spindle length.
Great minds.

I'm running a 111mm BB on my 1st gen DA crankset, and it's dead on, running a 13-21 rear. 52/42 tucks in just fine, about 3mm clearance.

I'm going to run a 108mm BB with my DA AX, though, as I'll be running a 28t rear cog, and I like it in tight on the big cogs.
My guess is that 1.5mm (per side) difference is going to put that 42T ring pretty snug in towards the chain stay, but clear it fine.
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Old 02-25-19, 11:02 PM
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Originally Posted by RobbieTunes View Post
Great minds.

I'm running a 111mm BB on my 1st gen DA crankset, and it's dead on, running a 13-21 rear. 52/42 tucks in just fine, about 3mm clearance.

I'm going to run a 108mm BB with my DA AX, though, as I'll be running a 28t rear cog, and I like it in tight on the big cogs.
My guess is that 1.5mm (per side) difference is going to put that 42T ring pretty snug in towards the chain stay, but clear it fine.
I think you'll find that the AX crank with the shorter BB spindle will actually give you a larger "Q" factor once it's all put together. DD pedals will give you a bit more "Q", too.

Between about 1982 and 1990 there were a lot of changes in BB length and crankarm angle. Part of this was the rise of mountain bikes with their need to clear angled chainstays Like dddd, I miss the days when you could experiment with chainline and Q factor just by changing the bottom bracket spindle.
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Old 02-26-19, 11:09 AM
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Originally Posted by Jeff Wills View Post
I think you'll find that the AX crank with the shorter BB spindle will actually give you a larger "Q" factor once it's all put together. DD pedals will give you a bit more "Q", too.

Between about 1982 and 1990 there were a lot of changes in BB length and crankarm angle. Part of this was the rise of mountain bikes with their need to clear angled chainstays Like dddd, I miss the days when you could experiment with chainline and Q factor just by changing the bottom bracket spindle.
The trend in the early 1980s was increased ankle clearance with the crankarm. To achieve this on the drive side, the crankarm/spindle interface was simply pushed inward resulting in the assymetrical spindles with a longer drive side protrusion giving way to shorter, symmetrical spindles. However, on the non-drive side, the crankarm had to built with additional outward cant towards the pedal end, increasing the Q-factor. Overall, the move to increased ankle clearance led to higher Q-factors and shorter, symmetrical spindles.

Shimano's first crankset designed for a shorter, symmetrical spindle and increased ankle clearance was the 1980 Dura-Ace EX Dyna-Drive crankset which was also used slightly later on Dura-Ace AX. It's symmetrical (English) spindle was 109mm versus the previous 112mm, assymetrical spindle.
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Old 02-26-19, 01:36 PM
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Originally Posted by T-Mar View Post
The trend in the early 1980s was increased ankle clearance with the crankarm. To achieve this on the drive side, the crankarm/spindle interface was simply pushed inward resulting in the assymetrical spindles with a longer drive side protrusion giving way to shorter, symmetrical spindles. However, on the non-drive side, the crankarm had to built with additional outward cant towards the pedal end, increasing the Q-factor. Overall, the move to increased ankle clearance led to higher Q-factors and shorter, symmetrical spindles...
I'm not understanding why moving the "hub" of the crankarm inward would increase the Q-factor at all.
Assuming that the newer crankarms were mounted on the appropriately-narrower new bb spindle, the Q-factor would seem to a design variable quite independent of the change to lower the "ankle" profile.

So I am thinking that if the Q-factor of certain of these low-profile cranksets did increase when redesigned, that it would have to do with wanting to add chainstay clearance (possibly for aluminum chainstays?) or to accomodate any increase in the chainline dimension.

Again, I am assuming that the crankarms and spindle dimensions would have been redisigned together as a system, so that changes in spindle width/offset would not force changes in the Q-factor or chainline.
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Old 02-26-19, 01:48 PM
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Originally Posted by dddd View Post
I'm not understanding why moving the "hub" of the crankarm inward would increase the Q-factor at all.
Assuming that the newer crankarms were mounted on the appropriately-narrower new bb spindle, the Q-factor would seem to a design variable quite independent of the change to lower the "ankle" profile.

So I am thinking that if the Q-factor of certain of these low-profile cranksets did increase when redesigned, that it would have to do with wanting to add chainstay clearance (possibly for aluminum chainstays?) or to accomodate any increase in the chainline dimension.

Again, I am assuming that the crankarms and spindle dimensions would have been redisigned together as a system, so that changes in spindle width/offset would not force changes in the Q-factor or chainline.
Yes, I believe you're understanding it correctly. It might have been more clear if they had explained that while the crank spider moved in, the pedal interface moved out. This resulted in arms that were more angled or curved as T-Mar alluded to.
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Old 02-26-19, 04:10 PM
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Originally Posted by dddd View Post
I'm not understanding why moving the "hub" of the crankarm inward would increase the Q-factor at all.

Assuming that the newer crankarms were mounted on the appropriately-narrower new bb spindle, the Q-factor would seem to a design variable quite independent of the change to lower the "ankle" profile.


So I am thinking that if the Q-factor of certain of these low-profile cranksets did increase when redesigned, that it would have to do with wanting to add chainstay clearance (possibly for aluminum chainstays?) or to accomodate any increase in the chainline dimension.


Again, I am assuming that the crankarms and spindle dimensions would have been redisigned together as a system, so that changes in spindle width/offset would not force changes in the Q-factor or chainline.

You could increase the heel clearance on the drive side without affecting the Q-factor. The spindle protruded further on the drive side, so you could shorten it and move the crankarm/spindle interface inwards. However, on the non-drive side, the shoulder of the spindle taper was already very close to the outer face of the cup, so the spindle couldn't be shortened any more without decreasing the spindle/crankarm interface and the integrity of crankarm in the immediate vincinity of the spindle. . Consequently, to achieve more heel clearance, the non-drive side crankarm had to have more offset at the pedal end, which increased the Q-factor. If you wanted to keep the Q-factor symmetrical on both sides, you had to go back and offset the drive side crankarm even more, which further increased the Q-factor.


Chain stay clearance was typically not a big issue. Even on racing bicycles, the chain stays were rarely shorter than 40.5cm. Consequently, increasing the rear spacing from 120mm to 126mm only reduced the chain stay clearance by a maximum of ~1.25mm for a 172.5mm crankarm.
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Old 02-26-19, 04:46 PM
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Originally Posted by T-Mar View Post
You could increase the heel clearance on the drive side without affecting the Q-factor. The spindle protruded further on the drive side, so you could shorten it and move the crankarm/spindle interface inwards. However, on the non-drive side, the shoulder of the spindle taper was already very close to the outer face of the cup, so the spindle couldn't be shortened any more without decreasing the spindle/crankarm interface and the integrity of crankarm in the immediate vincinity of the spindle. . Consequently, to achieve more heel clearance, the non-drive side crankarm had to have more offset at the pedal end, which increased the Q-factor. If you wanted to keep the Q-factor symmetrical on both sides, you had to go back and offset the drive side crankarm even more, which further increased the Q-factor.


Chain stay clearance was typically not a big issue. Even on racing bicycles, the chain stays were rarely shorter than 40.5cm. Consequently, increasing the rear spacing from 120mm to 126mm only reduced the chain stay clearance by a maximum of ~1.25mm for a 172.5mm crankarm.

Any problem with any of the clearances or Q-factor mitigation can be no worse on the left that on the right, even as the crankarm mounting hubs become symmetrical left-to-right with the bottom bracket, no?

Each arm has it's own 1/2 of the total Q-factor, and I just can't see the left arm ending up "worse" than the right under any circumstance.

Traditional crankarms were roughly symmetrical as well, just that the longer driveside spindle extension moved the chainrings where the designer wanted them and the right arm unfortunately moved further out than the left arm.
It can be hard to see the left and right arms being near-identical when the spider is in the way, and when the cup arrangement is different on each side.

Q-factor asymmetry can perhaps best be evaluated by measuring the pedal eye distance from the back rim. I do this often when choosing spacers for modern crankset installations. I have come to prefer moving things over to the left in order to better optimize the chainline for more-sporting riding conditions, but the real problem is that the designers use large q-factor for clearances at the stays and big chainline numbers seemingly optimized for 135mm rear spacing.

Last edited by dddd; 02-26-19 at 04:52 PM.
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Old 02-26-19, 05:07 PM
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I don't really get what's being said either. The NDS can always be made to be dimensionally identical to the right side, like a tandem crank. It's always the DS that has more dimensional constrains due to the FD/chainrings.

The only way I can figure the previous explanation making sense is if vintage cranks were very asymmetrical and the NDS Q was brought out to match DS Q, but I can't say I really remember cranks being like this unless they were triples or the NDS taper was worn due to BB maintenance.
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Old 02-26-19, 10:19 PM
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I just try stuff to see what fits.
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Old 02-26-19, 11:13 PM
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OP, try not to over think the scenario. Couple of basics I mostly follow, though stated 'mostly'. Meaning not carved in stone and have done and still do trial and error.

That said, I seek the spindle taper 'length' that's appropriate to the crank. They sometimes vary and can disrupt plans.

The classic chain line number is 43.5 mm, measured from dead center bb shell to middle of chain rings on a double OR the center ring on a triple setup. This chain line should follow to the middle of the cog stack. Again, this is a good baseline.

If you're pleased with that Dura Ace crank, use it. I imagine it's properly seated to the existing taper and you only need a shorter spindle. Subtract that difference to get that 43.5. So when you remove the spindle, you should be able to determine the differential length needed. If you can determine the brand and or interchangeable to the existing cups, its a go. If not, you probably can read the cups and note threads size (possibly Italian ... assuming you said old Bottechia) but anyways, get a complete bottom bracket to match threads and the shorter spindle, though make sure its listed to match the taper of that Dura Ace crank. Sutherlands guide will likely have those references.

Last edited by crank_addict; 02-26-19 at 11:19 PM.
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