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  • Knocking noise from Mega
  • rob8624
    Free Member

    Hi folks, just wondering if anyone has any input before I start stripping my bike down. I took the gamble and purchased a Mega (AXS, factory spec) from CRC before it closed, thankfully it all turned up and I absolutely love it, what a bike.

    Anyway. I’ve noticed a knocking noise that only happens when the left crank goes to it’s lowest point, it’s pretty audible, but only happens when the crank is fully weighed, if I’m sitting in the saddle it doesn’t happen. There is no performance difference in shifting, there is no knocking when bouncing and track standing, I’ve given the bike a once-over and everything feels solid, pivot bolts are all nice and tight, I know they can been loose on Nukeproofs, but all good. Pedals are new and I can’t feel any looseness in the bearings or anything.

    It’s hard to hear where it’s coming from as you can’t simulate it off the bike, I though it maybe a loose chainring bolt but I don’t think the SRAM setup has these? I’ve only ever worked on Shimano bikes, so bit unsure on how the cranks, BB an chainring work together. Maybe it’s the AXS, I hear the system can be cause annoyance if not setup-up spot-on.

    Any advice much appreciated. Obviously, the bike is new, it’s done like 50 miles over three rides.

    airvent
    Free Member

    Are the cranks fully torqued to spec?

    How old are the pedals?

    dartdude
    Free Member

    Remove crank arm and check BB interface first for torque & grease.

    Check not too much preload on BB

    Also grease the pedal threads

    molgrips
    Free Member

    There are reports of pivot bolts not being tight on these. I bought a Reactor and sure enough, knocking happened. It was a pivot bolt, the rear I think.

    rob8624
    Free Member

    Yea I’ve heard the same, I’ve checked by hand and all feels tight but will give them a nip-up.

    Pedal are brand new and greased. It happens at a precise point.

    molgrips
    Free Member

    When mine was loose it was obviously so.  You can tell by lifting and dropping the bike slightly, no need to take the wheels off the ground – you’ll feel the clunk

    rob8624
    Free Member

    Doh! Yea, just checked and rear non-driveside bolt was loose, and could be turned by hand. Sorted now all torqued up, no knocking.

    Loving the Mega btw, great bikes.

    molgrips
    Free Member

    Nice!

    It was a hard choice for me between Mega and Reactor, the fact Reactor was £150 cheaper was a key factor. I’m glad I got it though since I’d have gone for a 29er Mega and that would have been much too gate-like for my local woods riding and I’d have only been using it for days out, and I don’t do many of those.  I might’ve been happier with a 27.5 Mega though.

    rob8624
    Free Member

    Yea, I ride with someone who got a Reactor and they are perfect for general trail riding, big days out, was tempted to get one instead of the Mega as it’s not all about travel, right? But, the Mega suits the trails here in South Wales better than my Privateer which is kinda skittish and hard to get around the tight stuff, great bike for the Alps but yea Mega all day long.

    noeffsgiven
    Free Member

    When I buy a new frame the first thing I do after checking alignment is undo the pivot bolts and thread lock them to the correct torque, I just don’t trust them to be done up right from the factory as I’ve had a few pivots  with zero thread lock on and the first bolt I checked on my latest frame was under torqued by almost a quarter of a turn.

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