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There is visible rust where my left crank arm meets the bottom bracket which I believe is the cause of the creaking (only present when pedalling hard on left side).

Is it okay to spray WD40 in there to get rid of the rust?

Thanks Mark

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WD40 won't actually get rid of rust, though it will slow the rate at which it gets worse, for a little while.

However surface rust there shouldn't lead to creaking, because nothing should be moving against it, so I'd be more concerned with checking that everything is tight that should be tight, and moving parts move freely.

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  • So I should remove the crank arm and wipe away the rust. Then apply wd40 and screw the crann arm back in?
    – Mark McGovern
    Commented May 29, 2020 at 13:15
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    Yes, except I'd use something longer lasting than wd40, either a thin smear of grease or a wipe of oil.
    – Chris H
    Commented May 29, 2020 at 13:30
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WD-40 is a penetrating oil. It will happily creep past the seals of the bottom bracket and thin out the grease lubricating your bottom bracket bearings. Once the grease has thinned, it won't lubricate the bearings as well, and it will want to work its way back out the same way the WD-40 got in in the first place.

You'll end up needing to repack the BB more frequently (until the WD-40 finally wears off), or you end up wearing out the BB bearings and having to replace them.

Don't spray penetrating oil near seals that hold back grease.

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The creaking could be from the bottom bracket. you should first assure that your crank arms are properly tight on the bottom bracket spindle, then ride. If you hear creaking, then check the bottom bracket.

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  • I initially though of the bottom bracket. But why would it only be happening when I pedal on one side?
    – Mark McGovern
    Commented May 29, 2020 at 13:27
  • The two cups of the bottom bracket are slightly different in most designs, and are independently tightened into each side of the shell (frame). So one side might be slightly turned lose and creaks when enough force is exerted on that side. I would still first check that the cranks are fully pressed on, because that would be an easy fix and rule out the crank arms if its not the problem.
    – bradly
    Commented May 29, 2020 at 13:38
  • Creaks are magical, BB to frame strong contender, but could also be: frame crack, pedals (internal and pedal to crank), chainring bolts, crank to BB taper, and many other more apparently unrelated components..
    – Lamar Latrell
    Commented May 31, 2020 at 1:00
  • @Lamar Latrell It could be. It could be any of those things but he's got to start somewhere, wrenching a crank arm bolt is a good place to start. Then BB cups, because it sounds like that is what is going on based on his brief description. I've only cracked a few frames in my life, but the sounds the cracks made were not regular as he described. I ruled out chain ring bolts because he hears it only when he puts force on the left side, and the crank spider applies constant force to the ring unlike the crank arm to BB
    – bradly
    Commented May 31, 2020 at 3:02

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