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Deore Cranks - retaining plug thing

paul.skibumpaul.skibum Posts: 4,068
edited July 2012 in MTB workshop & tech
At some point I lost the little retaining plug thing in the non drive arm of my deore cranks.

At some other point the grub bolts have worked loose. On my last ride I was waiting for some friends, rode of a log drop and noticed the problem (because both my cranks dropped to 6 o clock with a nice graunchy ripping metal sound) :cry:

I managed to clean up the splines, re align the cranks and put them in position and do up the grubs enough to ride but wasnt really pedalling (riding the lift and with beginners so not needing to put in a lot of effort).

I only reinstalled the cranks a few weeks back and I "know" I did the bolt up and the pinch bolts, have installed cranks like these loads of times. That said I assume I fu-ed up somewhere along the line and missed a step.

Question is - if I have the pinch bolts doen up and have made sure the crank is in the correct position, do I need the plastic bolt? And if I have damaged some of the splines am I looking at a new crankset in the near future?
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Posts

  • lordmerchantlordmerchant Posts: 378
    assuming you are running an external BB here....pretty sure the plastic bolt is for pre-loading the bearings, therefore without it you will get side to side play, which can naff up any number of things. Could also cause damage to the splines on your axle. Not good at all, I'm sure you can get a replacement for a few £ from chainreaction.
  • andrewjosephandrewjoseph Posts: 2,165
    The plastic 'plug' is to preload the bearing as stated. once the pinch bolts are done up then you can take it out.

    However, once the the pinch bolts work loose this preload is gone. i keep a spare 'plug' and matching preload tool in my wife's mtb toolkit (her deore cranks have lasted much longer).

    I've had the splines wear on a pair of my old deore cranks, so went to race face which have a different design. once the splines go the crankset is useless.
    --
    Burls Ti Tourer for Tarmac, Saracen aluminium full suss for trails
  • ilovedirtilovedirt Posts: 5,798
    Yes, the preload bolt is essential.
    I've had this happen on my SLX cranks before when I had the crankset spaced out wrong due to my chain guide not fitting very well, mashed up the splines a bit, but it went back on again with some fettling and has been fine ever since.

    Andrewjoseph - I've found Shimano cranks to be much more reliable than Raceface for that very reason! I've got two ruined sets of Raceface cranks, but my Shimano ones are still going strong after a good couple of years of abuse.
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  • The RookieThe Rookie Posts: 27,803
    I'm concerned you say you know you did that bolt up, it's not something to do up, but something to preload the bearings, do it up in a conventional sense and you just ruined the bearings.
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • Chunkers1980Chunkers1980 Posts: 8,035
    or crack the threads. You should also have a tab to stop them falling off and when the pinch bolts are done up properly you can't actually turn the pre-load cap.
  • andrewjosephandrewjoseph Posts: 2,165
    ilovedirt wrote:
    ...

    Andrewjoseph - I've found Shimano cranks to be much more reliable than Raceface for that very reason! I've got two ruined sets of Raceface cranks, but my Shimano ones are still going strong after a good couple of years of abuse.

    Just speaking as I find. The shimano deore lasted me 18months/3600 km until october 2006. The raceface has been on there since, 10000 km and counting.
    --
    Burls Ti Tourer for Tarmac, Saracen aluminium full suss for trails
  • snotty badgersnotty badger Posts: 1,593
    I would imagine that if you've managed to spin the crank arm on the splines that they're pretty shagged now.

    I've been using Deore HT2 cranks for 4 years now and never had a crank just work loose. At least Deore cranks are pretty cheap to replace. Lesson is check your nuts!
    08 Pitch Pro
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