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New crank arm not fitting tapered axle

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New crank arm not fitting tapered axle

Old 08-03-21, 07:42 PM
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Generald1sarray
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New crank arm not fitting tapered axle

I recently bought an old bike (around 2009 specialized tricross) online. It needed a new crank shaft, I got the setup from a local shop however it doesnít seem like it fits in properly. I thought the gap was normal until the crank arm almost wobbled off during a ride this weekend. Any idea how to fix this? The local shop has a three week wait time to get in
The site wonít allow me to upload any pictures but itís out quite a bit. Maybe half an inch?
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Old 08-03-21, 08:11 PM
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Old 08-03-21, 08:18 PM
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Ok,
Do you have a photo with the crank installed, but the bolt removed?

I would probably remove the crank arm. Lightly grease the spindle, and put it back on. And, keep tightening the bolt if you can.

I think the crank should go about 3/16" further down on the spindle. Ultimately the bolt will be fairly tight. I do most of my personal work by feel rather than torque, but someone should have torque specs.

If you ride the bike with the crank arm loose, you risk hogging out the arm, and permanently ruining the crank arm.
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Old 08-03-21, 08:30 PM
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It's a 'bottom bracket' not a 'crank shaft'. How tight did you get that bolt? It's supposed to be very tight, old man strength tight.
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Old 08-03-21, 08:43 PM
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Originally Posted by cxwrench View Post
It's supposed to be very tight, old man strength tight.
LOL, I don't think I've ever torqued a crank on a square taper BB.

Definitely looks like that arm should be further on the spindle. Don't ride it like that.
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Old 08-04-21, 03:38 AM
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Does the spindle have the correct taper for the crank arms? I'm thinking the new BB might be ISO taper and the arms JIS or vice versa?
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Old 08-04-21, 06:15 AM
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Originally Posted by CliffordK View Post
Do you have a photo with the crank installed, but the bolt removed?
+1 this.
Attached Images
File Type: jpg
crank-arm-seat.jpg (79.2 KB, 85 views)
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Old 08-04-21, 06:17 AM
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The possible ISO/JIS mismatch was my first guess.

Looking at the pictures, though, I think some grease and a torque wrench might be the answer. There's always been some back-and-forth over greasing the taper of a BB, but that crank looks like it needs some help. So grease the taper, grease the crank bolt, tighten it to the torque spec (50 Nm is flashing in my head, but better to look it up than rely on a possibly faulty memory). That sequence should seat the crank on the bottom bracket, and with adequate torque, it's unlikely to go anywhere.
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Old 08-04-21, 08:35 AM
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Originally Posted by CliffordK View Post
Ok,
I would probably remove the crank arm. Lightly grease the spindle, and put it back on. And, keep tightening the bolt if you can.
Originally Posted by pdlamb View Post
I think some grease and a torque wrench might be the answer. There's always been some back-and-forth over greasing the taper of a BB, but that crank looks like it needs some help.
Don't do this, ever. A square taper is a friction fit, grease is an anti-friction lubricant and does not belong on a square taper.
I would bet money that it isn't tight enough. Skip the whole torque spec on a crank and just tighten it. When I tighten I start with the drive side, I use an 8mm allen socket in a 16" long ratchet and use the wheel as my leverage. I tighten till it really just doesn't want to tighten more, then I use the drive side pedal as the leverage for the non-drive crank arm. Again till I can't tighten more. Then go ride. I've never seen a crank bolt break so don't worry about that. But it really is one of those tighten like crazy spots since you want it to never come loose.
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Old 08-04-21, 09:32 AM
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Having information from a torque wrench is good if you (like the OP) don't know what you're doing, though. 30 ft-lbs is 30 ft-lbs.

We have no idea what he'll get from telling him "Just tighten it like a man!"
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Old 08-04-21, 10:18 AM
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EXCELLENT diagram !!!!

Thank you for posting JDT !!!

much appreciated !!!
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Old 08-04-21, 03:31 PM
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Originally Posted by Russ Roth View Post
Don't do this, ever. A square taper is a friction fit, grease is an anti-friction lubricant and does not belong on a square taper.
I would bet money that it isn't tight enough. Skip the whole torque spec on a crank and just tighten it. When I tighten I start with the drive side, I use an 8mm allen socket in a 16" long ratchet and use the wheel as my leverage. I tighten till it really just doesn't want to tighten more, then I use the drive side pedal as the leverage for the non-drive crank arm. Again till I can't tighten more. Then go ride. I've never seen a crank bolt break so don't worry about that. But it really is one of those tighten like crazy spots since you want it to never come loose.
Wrong. A thin layer of grease on the flats will not hurt anything. I have been doing this for over 25 years problem free. Everything on a bike (fastener wise) is a friction fit and you grease all of them. Not greasing square taper cranks/axles is nothing more than a myth. Since everyone loves a little Sheldon:"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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Old 08-04-21, 04:01 PM
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As far as greasing the tapers and torque, Campagnolo recommends putting grease on the taper and 28 ft-lbs of torque.
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Old 08-04-21, 06:56 PM
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Thanks for the tips everyone! Turns out you were all right, just needed to tighten the bolt. I wasnít sure if I could over tighten the bolt or not.
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Old 08-04-21, 10:27 PM
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Originally Posted by Generald1sarray View Post
Thanks for the tips everyone! Turns out you were all right, just needed to tighten the bolt. I wasnít sure if I could over tighten the bolt or not.
Thank you for letting us know that the problem was resolved.

Cheers
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