Friday, November 18, 2011

Cross bike update - Mounting BB and Crank

The crankset arrived, and it's high time to mount this thing up! My initial observation of this crank is that it is a little heavy. It looks nice, and was inexpensive, so this is something that was expected. Hence the Cheap / Light / Cool venn:

Since the dawn of time

Overall, this will be a great crankset, meeting the important points as well as being strong. The bottom bracket is the first thing to install in the frame. The bottom bracket consists of two sides and a middle spacer. Each of the bearings is threaded differently, one for left, and one for right. They are labeled as such, as well as a 'DO NOT OPEN' warning, as they are sealed, there's no reason to open them up.

Left bearing Center spacer Right bearing

Make sure you put the plastic center piece between the bearings. When threading them in, it's a good idea to put some grease on the threads. This will ensure they go in smooth, keep moisture out and keep the creaking to a minimum. Just glob a little of this on the threads and carefully tighten them.

Grease it up!

On this image you can see the indication of which side of the bike the bearing goes on, as well as an arrow showing which direction to turn it to tighten it. One side is reverse threads, just like pedals. Also indicated on the bearings is the amount of touque you should use when tightening them. This was 40-50 Nm, which is some measurement of torque. Once the bearings are hand tight, you use a special tool to tighten it.

Bearing tightening tool

This tool fits over the bearing snugly. I have a comically large torque wrench and here it is in action:

Torque wrench

Once the bearings are in tightly, putting the crank in is a fairly simple process. Stick the drive side into through the bottom bracket and attach the non-drive side. The non-drive side has two clamp bolts that will fix it to the spindle. There is a small tightening bolt that will tighten the crankset laterally. Tighten this before you tighten the clamp bolts.

Tightening bolt

This bolt is often made of plastic or composite - this is an indication that you shouldn't tighten it more than necessary. When the crankset is satisfactorily tight, tighten the clamp bolts to lock on the non-drive side.

The clamps!

This should also be done with a torque wrench. This tool is pretty important, especially if you're going to be working with carbon parts (stem, seatpost, bars). The crank is now tight, and ready for a chain and pedals!

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