Saturday, 5 May 2012

The Build Part I: Power-Torque cranks

So to recap, I have bought my Cinelli Saetta frame and fork through my local bike shop, Howes.  The frame-set comes with its own Columbus headset and Cinelli-branded seat clamp.  My local bike shop fitted them all together for me with the Vai Bianca stem.  The next step for me was to protect the frame with pipe insulation (to prevent knocks during the build) and then fit the saddle and seat post.  I have hooks set up which allow me to suspend my bikes by stem and saddle so fitting these allows me to use the hooks as a work stand.

This seems like an excellent opportunity to introduce an emerging source of information on bike maintenance:  People who work in the IT industry will be familiar with programmers' Q&A site StackOverflow.  There is a brief wikipedia page on the history of this site.  The stack exchange concept takes the success of this original idea and attempts to stamp it out across a wide range of topics.  The stack exchange on the subject of bicycles seems to be well populated with content.  I put this down to common elements between the mentality of the DIY-bike mechanic and the mentality of the programmer.  So if you are attempting to apply experience gained fiddling with computers to the more mechanical realm of fiddling with bicycles this site will probably be speaking your language.

It seems that my ceiling hooks have saved me from the dilemma of working on a carbon bike using a traditional work stand.  To summarise this thread from stackexchange, if in doubt don't do it and whatever you do don't do up the clamp too tightly!

In my last post, Cranky Delays..., I discussed my choice of gears and chain rings.  Installing the cranks seemed like a sensible first step but as I worked on the bike from my eye-level hooks I did realise that there was a better way to work on the cranks when you need to tighten things up - just add wheels!  It seemed much easier and more natural to applying the forces required to install the crank set with the bike on the ground with wheels and tyres fitted.  I guess it does depend how far from the ground you are.

I've installed a few square-tapered bottom-brackets over the years but the new breed of cranksets with their outboard cups and hollow axles are a completely new experience for me.  The instructions that come with the crankset are pretty scary, emphasising the need to face the bottom bracket before installation.  I actually checked back with the frame dealer before proceeding but they reassured me that the shell was ready to take the new cups and my measurement of the shell width came in at 67.87mm which is within the tolerance.

Fresh from my experience with the chainring bolts (which were stuck fast with thread lock) I must admit I was concerned about the amount of thread locking compound on the supplied cups.

I recall a stuck bottom bracket in my Bianchi many years ago, my local bike mechanic had a neat trick for removing it.  He removed the crank, closed the shop, then welded the spindle to the bottom bracket shell.  Once it had cooled, he refitted the crank and used that to unscrew the shell.  A few scorch marks later and I was upgraded into the world of cartridge bearings.  His summary of the situation: somebody was being mean with the grease.

The instructions that come with the crankset don't mention the need to apply a thread locking compound and in a close look at the installation video it appears that the threads are clean too.

One of the problems with information on the internet is that it tends to be strongly biased towards people with problems.  Bike riders with noiseless, trouble free bottom bracket installations are probably not logging on to complain or post to forums about the issues they're having.  Hopefully they are out riding and enjoying their bikes!  A search for the similar but high-end ultra-torque will throw up threads like this one from the RogueMechanic.  There are all sorts of interesting bits of information (and doubtless mis-information) in this post and its associated comments.  Anyway, for comparison here are the two videos of the Ultra-Torque installation:

Notice that the first 5 minutes of this video show the preparation of the shell, which emphasises the importance of this step.  It is interesting that they left this out of the Power-Torque video.  If you aren't content with doing something the correct way you can always follow the inferior (incorrect?) procedure instead, also documented in an official video!  This one uses copious quantities of Loctite 222, a liquid thread locking compound.

Given that thread-locking compound is basically glue, and that my experience has been skewed towards things getting stuck fast rather than shaking loose in this department, I scraped some of the thread lock out (it would be impossible to get it all out without a suitable solvent I think), applied some grease and tightened the cups up to the recommended torque.

Unlike the bike in the first video, which appears to have right-hand threads on both sides of the shell, my bottom bracket is BSA or 'English' threaded so you have to do up the drive side anti-clockwise.  There is a good article on Wikipedia about bottom brackets in general, including the various sizes.  When ordering the Power-Torque cups you do need to know which you have.  The reason that the drive side has a left-hand thread is to reduce the tendency of precession to undo the cups - the fact that it goes backwards may seem unintuitive but the linked article has a cute animation which demonstrates the effect so that you don't have to do the maths yourself.

If you are convinced that precession is your enemy here then the risk of loosening must be greatest on the drive-side of an italian threaded bottom bracket.  I expect I'll take the drive train apart for servicing at some point and I'll report back on the torque required to undo them - if I have a suitable torque wrench, which brings me to a bit of a gripe...

To help me get the torques right on this part of the project I bought a new torque wrench, on special offer, for a surprisingly cheap price.  I have a small wrench that goes up to 25Nm but this is not enough for the cups, the crank fixing bolt or the pedals.  The wrench I bought was a draper 1/2" drive ratchet type wrench.  I bought it from a fabulous local hardware shop called Mackays - this shop is famous in Cambridge for having the type of expert staff who can find replacements for pretty much any type of weird fixing you throw you at them.  Anyway, the wrench has a reversible ratchet and a scale marked from 30Nm up to a blood-vessel bursting 210Nm.

Armed with my new torque wrench I set about the cups, with the aid of the special purpose Campagnolo tool (I had expected this tool to fit more snuggly on the cups).  I started on the left (non-drive) side of the bike and tightened the cup without any problems.  I then flipped the ratchet and started tightening the drive side.  As I was just learning to use this tool I set the torque to the lowest setting each time (30Nm) to help get the feel of the thing before tightening to the recommended torque.  This was a good thing, because as I tightened the drive side I quickly realised that I was having to put in more effort than expected to get the wrench to break away.  It was only later I noticed the small print on the leaflet that came with the wrench: "IMPORTANT: The torque wrenches detailed in this instruction leaflet are for right hand torquing only.  They are not designed for left hand use."  I finished tightening the drive-side cup by flipping back and forth with the ratchet until I could no longer undo the cup using the specified torque.

So my gripe is why advertise these wrenches as having reversible ratchet heads?  Obvious you might say, it allows you to undo things, just like the guy in the Campagnolo video who clearly uses a similar torque wrench to undo the cups.  But this doesn't explain it, the warnings section of the leaflet kicks off straight away with "Never use the torque wrench to undo bolts, nuts or fasteners, as this will damage the ratchet and the calibrated setting".  I reckon that, at this price, they know that the tool will not be worth calibrating and that it will turn in to a fancy breaker bar after a year or two of use.

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