Cranks And Pedals - Mountain Bike Zen
Crank Interfaces
There are three main types of crank interface. The square tapered crank is where the crank arm fits onto a square shaped crank fitting which is fixed with a nut. This is not a good crank for a mountain bike. It is okay for a road bike or child's bike and tends to be found on cheaper and older bikes, but with this system on a mountain bike you are much more likely to cause damage and end up with a shredded crank fitting and a useless bike.
An isis crank has more pointy bits on the crank arm to grip the crank but works pretty much in the same way as the square tapered crank. The advantage is the extra splines provide a sturdier fit and these fittings are much more rigid and can take more abuse.
Finally you have external two piece bottom bracket sets. With this you have one crank arm and a bracket that screws through the frame and the crank arm fits inside of this. These are stronger units and are much better for mountain biking.
Maintaining your bottom bracket is fairly straight forward. Firstly you will notice that there is some unusual play , movement or noise when pedalling. Once you have identified that the bottom bracket is the issue remove your crank arm, then remove the crank, finally check the bracket cups, tightening these may resolve your problem, if not you may need to replace the bearings or possibly the whole bracket.
If replacing the bracket it may be a good opportunity to replace the crankset too, if not you need to make sure that the bracket you buy will match the crank fitting.
Specialist tools are unavoidable when fitting a crankset, you can try with an adjustable wrench but you are at a very high risk of rounding of the tapered edge and ruining the hardware before you have even had chance to use it. Again this is a job best left to a bike shop if you are unsure as it will save you time and money in the long run. Loose pedals will lead to injury.
A good modern bike tool set will usually contain the necessary tools for tightening and removing your crankset.