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Old 10-19-05, 01:11 AM   #1
tour de low
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When I slide my left crank arm onto the Dura Ace 7800 crank spindle, there are 2 mm of spline still visible in the arm. In other words, it's obvious the arm is not seating all the way. If the crank is off the bike, the arm seats all the way. My bottom bracket shell is exactly 68mm wide, like it's supposed to be, and both bearings are threaded all the way in with the supplied tool, and there is no gap between the shell and bearings. My spindle is 110 mm long, and I measured another 7800 spindle at a bike shop today, and it was exactly the same length. It JUST DON'T SEEM RIGHT! The splines are only 11 mm long. If I can see 2mm not engaging, that's only 9 mm width of splines in effect. A BIC pen is 8 mm wide. If I can't fix it any other way, I'm going to file 1mm of length of both ends of my BB shell!

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Old 10-19-05, 02:49 AM   #2
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I don't know about Shimano's cranks in particular, but I know that FSA Gossamer MegaEXO cranks do the same thing. I think they're designed with tolerances for spline engagement so that imperfect (narrow or wide) bottom bracket shells won't cause problems. I doubt that a 2mm difference spline engagement would make a difference in how well it works -- the power is still transferred just fine and there's no slipping, right?

If you filed down your BB shell, you should also get it faced. And then you'd have a 66mm BB shell, which might not work with any other bottom brackets. Don't do it.
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Old 10-19-05, 07:56 PM   #3
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The 5th bike shop I went to in two days explained it to me. You tighten that "dust cap" before you tighten the arm bolts. It says to do so in the instructions. It doesn't say why- I thought it was just a dust cap you could even leave off the crank. It only says to tighen it 4-6 inch lbs. I think it has to be tightened a lot more than that to take up spline length. If I tighten the cap as much as I can with the plastic tool it comes with, I only have 1mm of unengaged splines showing instead of 2. What has happened is the o-rings have been compressed, and now there's a lot of drag on the crank spin- I don't like that either. I bet Lance takes the o-rings off. The Shimano site flatly states "Have your BB faced" like it's not even an option. Why isn't that recomended in the instructions that come with the crank?-there's a bit of length right there.

Last edited by tour de low; 10-19-05 at 08:47 PM.
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Old 10-19-05, 11:49 PM   #4
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Quote:
Originally Posted by tour de low
When I slide my left crank arm onto the Dura Ace 7800 crank spindle, there are 2 mm of spline still visible in the arm. In other words, it's obvious the arm is not seating all the way. If the crank is off the bike, the arm seats all the way. My bottom bracket shell is exactly 68mm wide, like it's supposed to be, and both bearings are threaded all the way in with the supplied tool, and there is no gap between the shell and bearings. My spindle is 110 mm long, and I measured another 7800 spindle at a bike shop today, and it was exactly the same length. It JUST DON'T SEEM RIGHT! The splines are only 11 mm long. If I can see 2mm not engaging, that's only 9 mm width of splines in effect. A BIC pen is 8 mm wide. If I can't fix it any other way, I'm going to file 1mm of length of both ends of my BB shell!


Are you sure that the spindle length is 110mm? What is the actual published spindle length from Shimano?
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Old 10-20-05, 02:26 AM   #5
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Like I said, I compared it to another one, and the spindles were the same length. I got mine a year ago. The one I compared it too was new and at a different bike shop.
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Old 10-31-05, 01:20 AM   #6
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Here's an up-date. If you are putting this crank on a bike that didn't come with it, face the BB shell. I slid a cigarette rolling paper between the shell and a barely snugged down bearing, and the shell face wasn't square - on both sides. Using this method, I faced the BB shell myself with a file. Then I took the shell width down to 67mm. With the left crankarm o-ring removed, and the "dust cap" fully tightened, the right crank arm was nearly fully seated. When the 0-rings compresses and wear, (along with the nylon they rub against) I will take up that last bit of slack. I feel a lot better now. Glad I took it down 1mm under official spec. These splines are about as thick as a mechanical pencil lead, half as tall, and the ones in the arm are aluminum... It's borderline engineering in my estimation.

Last edited by tour de low; 10-31-05 at 01:43 AM.
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Old 10-31-05, 06:41 AM   #7
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Originally Posted by tour de low
The 5th bike shop I went to in two days explained it to me. You tighten that "dust cap" before you tighten the arm bolts. It says to do so in the instructions. It doesn't say why.
I saw that in the instructions as well. Tightening the left arm's pinch bolt on without first tightening the dust cap is analogous to tightening the pinch bolts on your threadless stem without first tightening the top cap... Makes sense that you saw what you did.
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Old 10-31-05, 09:16 AM   #8
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Quote:
Originally Posted by tour de low
Here's an up-date. If you are putting this crank on a bike that didn't come with it, face the BB shell. I slid a cigarette rolling paper between the shell and a barely snugged down bearing, and the shell face wasn't square - on both sides. Using this method, I faced the BB shell myself with a file. Then I took the shell width down to 67mm. With the left crankarm o-ring removed, and the "dust cap" fully tightened, the right crank arm was nearly fully seated. When the 0-rings compresses and wear, (along with the nylon they rub against) I will take up that last bit of slack. I feel a lot better now. Glad I took it down 1mm under official spec. These splines are about as thick as a mechanical pencil lead, half as tall, and the ones in the arm are aluminum... It's borderline engineering in my estimation.
What were you wraping in that "cigarette rolling paper"?

There is no reason to cut the shell to 67mm. The design of the left side arm attachment allows for normal variation in bottom bracket shell width.

Regarding using a file to face the shell, this sounds like something I might try on some POS frame but not on a frame worthy of 10 speed Dura Ace. Facing the frame properly only takes a few moments with the proper tools, why not find someone to do the job right?
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Old 10-31-05, 09:46 AM   #9
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Originally Posted by Nessism
What were you wraping in that "cigarette rolling paper"?

There is no reason to cut the shell to 67mm. The design of the left side arm attachment allows for normal variation in bottom bracket shell width.

Regarding using a file to face the shell, this sounds like something I might try on some POS frame but not on a frame worthy of 10 speed Dura Ace. Facing the frame properly only takes a few moments with the proper tools, why not find someone to do the job right?
Careful, this guy is questioning Shimano's borderline engineering. ..Apparently after wrapping some vintage '70s green shag in that rolling paper.
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Old 11-01-05, 12:35 AM   #10
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I'm 52. I was riding a Bianchi in 1970 when I upgraded to tubular rims and a Campy front De-railer. I bought the first BMX specific bike when it first appeared around 1975- a Redline with cast aluminum wheels. I own Cannondale road and Mountain bikes. I've got a Schwinn Stingray Chopper just to look at. I've owned 16 motorcycles, did all my own mechanical work. I've rebuilt car engines, worked as a machinist. - If you follow the instructions, you'll never even know these cranks are faulty-you'll never SEE it! I FEEL LIKE I'VE BEEN TAKING CRAZY PILLS! The effective bore length of the crank arm spindle hole is 18mm, If that length were splined, I might let it slide, But 7mm is just smooth - Spline length is only 11mm- That's not much. Your rear axle is 10mm. You can't have only 9mm of tiny aluminum splines engaged and call that reasonably sturdy. The bike shop said they'd face the shell for just 10 bucks if the crank was out. But after the zig zag operation, tightening the bearings left a mark on any high spot. I just took off the high spots untill they didn't appear anymore. Removing a whole millimeter isn't your typical facing job, and I had to do it myself to get it exactly where I wanted it.

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