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The owner's manual on my new bike (with the new Shimano Claris, not the old one with Octalink) asks me to do this:

After the first 20 km tighten the crankset and also tighten the pedals in the crank arms. Check if crank bolts are properly tightened. Check whether left crank arm screws are tightened firmly when bottom bracket axle is integrated with right crank arm.

I found many tutorials on the web they are about assembling the cranks, replacing them and they all include removing the cranks. But if I understand the manual, it specifically instructs me not to do that and leave such operation to a specialist:

Important warning! No check of crank arms fastening ... may result in ... Such damaged crank arms must be replaced with new crank arms. Please contact special bike service for crank arms replacement.

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  • The manual tells to leave everything to a specialist. – ojs Aug 3 '18 at 8:47
  • Well, the Merida manual for my older MTB bike contained a lot of information, even how to pump the suspension and similar advanced things, but this one has nothing of that sort. And the components are completely different. – Vladimir F Aug 3 '18 at 9:05
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    What's your actual question? Are you asking if you are allowed to do maintenance on your bike yourself? – Argenti Apparatus Aug 3 '18 at 11:09
  • Not at all! It is in the title. How to tighten the cranks. How to do this specific step, which the manufacturer wants me to do, without taking the cranks down. I thought that I might need the tool for the silver brackets, but as the video linked by Andrew Henle shows, it is about two bolts on the left crank and the black screw(cap). The manufacturer specifically asks me to do it so why would I even ask whether I am allowed to do that? – Vladimir F Aug 3 '18 at 11:25
  • It tells you not to do what??? – Daniel R Hicks Aug 3 '18 at 19:15
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Park Tool's website has quite a few "fix your bike" tutorial videos. You may have already seen this one:

Crank Removal and Installation - Two Piece Compression Slotted (Hollowtech II, FSA)

I do wonder how many bike shop mechanics go to Park Tool's website and watch the videos for tips on how to work on obscure parts.

In this case, "how to tighten the crankset" is a necessary part of installing such a crankset. For this video, that starts about the 4-minute mark. In this case, all you probably need to do is get the proper Allen wrench and make sure the two clamp bolts are tight. (And that doesn't mean King Kong tight...)

There's nothing special about doing your own bicycle maintenance - there's nothing really hard about any of it. Even building your own wheels from parts is actually easy if you have the patience and can be done with just the proper spoke wrench (preferably a good butterfly one, as using some of those tiny spoke wrenches to build a wheel can be tough on the fingers). In some cases, you will need special tools. For a Hollowtech II crankset removal, you need something like a Shimano TL-FC16 Crankset Arm Tool to get the dust cover off. (Hint - you have to loosen the two Allen bolts holding the crank arm tight to get that cover out...)

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  • Thank you. Perhaps it is only needed when I discover some looseness as shown at time 5:50? The instruction in the manual was probably generic for various kinds of cranksets. – Vladimir F Aug 3 '18 at 11:27
  • @VladimirF Perhaps it is only needed when I discover some looseness as shown at time 5:50? Exactly. Though I've never had a Hollowtech II crank work itself loose, but it might be possible. Something like that is probably poor assembly, especially on a new bicycle. It's usually a good idea to go over a new bicycle and make sure everything it properly assembled, and the crankset being tight would be one of the many things to check. You don't want to find out while riding that your shifter lever wasn't properly tightened on the handlebars. – Andrew Henle Aug 3 '18 at 12:19
  • You guys seem to be talking sense. The whole question started because the manual wants these kind of checks done after 20km. Like tightening the wheel nuts on a car after 200 miles. It’s certainly possible for pinch bolt cranks to work loose. Shimano use that safety pin sandwiched in the gap to stop left arm falling off if it does loosen. Manual is generic, in OP first quote it mentions crank bolts and crank screws, ie covering Octalink and Hollowtech II – Swifty Aug 3 '18 at 20:01
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I think you are confusing the tightness of the clamping of the crank arm onto the axle with setting the bearing preload.

Clamping of the crank arm onto the axle is accomplished with the two pinch bolts. I believe your owners manual just wants you to make sure these two bolts are tight. Ideally you would use a torque wrench to do this.

The bearing preload is set by the black plastic cap before tightening the pinch bolts when installing the crank arm. Unless the left crank arm came loose the preload should be fine. You can check for play in the axle as shown in the video.

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I think the implication is that anytime you install these types of cranks, when you’ve ridden for 20 km you are then expected to tighten up/torque check the two pinch bolts again.

If you were to loosen the bolts for any reason, you would torque check them when you tighten them up and again after the first 20 km. So the manual is instructing you not to disassemble the cranks but partly because in this context you would be resetting that 20 km ‘clock’.

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