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Home mechanic help
In the vain effort of trying to improve my mechanical skills I am slowly rebuilding a bike. In this I have just put in a new set of XT cranks and bottom bracket – seemed easy enough. Although I did have to tap the crank with a wooden mallet to pop it through the BB. Not a big wack, just a gentle tap – is this usual? It seemed to be just getting the end to clear through – this was also the case when not on the bike so I am happy things are square.
Secondly, given it is brand new how freely should it spin? It spins easily, but not as freely as my older ones. It does not feel as though there are any tight spots on the rotation, so I am hoping that it will free up. Will it? But, past experience (starting a race with “it will be ok, it will free up as I go along”) suggests that hope is not a strategy.
I did follow the instructions from previous forum threads, loosened the little star shaped locking nut on the non drive side which helped.
Cheers C.
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I usually have to hit my XT cranks with something to get them through the BB - pretty normal. However, I usually put a bit of grease on the axle and inside the BB to help it slide through.
As to how freely they spin when in place - they should spin freely even with the star lock nut tight. Did you check the BB width is correct and you have the correct number of spacers (if any)?
Your light tap is fine. I use a rubber mallet for the same purpose.
The objective of the star nut is only to take out the end float on the crank spindle. Should have almost no pre-load. Any more preload than that and it binds up the cranks and shortens the bearings' life. You can tell quite easily if you've gone too far as the bearing resistance increases noticably.
+1 to the above poster - grease on the crank spindle on assembly is a good thing. Wipe off any excess outside as that attracts dirt and turns it into a grinding paste.
Grease was certainly part of the build process. I will look at the spacers. I copied what came off (it was SLX) in terms of spacers, and did measure. But I will do this again.
What is the risk of taking one out? I ask as (and yes I can feel a numpty tag emerging) the chain rings are fractionally wider than they were before (using the front derailleur as a guide). I was ready to adjust the derailleur, etc, and it is only a fraction out, but possibly only by the width of a single spacer. Maybe I can solve two issues at once.....