BMC Fourstroke FS04 (update 3)

You may have been wondering what happened to the BMC mountain bike restoration project I started a while back.

Like many projects it got to the “nearly finished” stage and sat there for a good six months causing a nuisance to the family. 

Good news that it’s now moved on to the “basically finished” stage…

It was cleaner, but is now dusty from riding. So apologies for the photos, but it’s great that it’s rideable!


On an earlier test ride, I noticed the left pedal crank creaked on the downstroke, which it didn’t on my first test. This suggested a worsening issue, so I inspected further.

Anything other than a smooth bottom bracket/crank is bad news. A lot of torque goes through there, plenty to cause damage pretty quickly if not addressed. 

I found an allen key large enough to remove the pedal cranks, and discovered a Shimano Octalink bottom bracket. This is the first Octalink system I have owned, with all my older bikes having square taper BBs. 

I also found the non-drive side (left) mating splines to be slightly chewed at the end. Apparently this is common with Octalink systems, and happens when the crank arm isn’t perfectly aligned, prior to screwing the crank arm bolt back on. So, as I had never removed it, this damage was done by the previous owner, though it seems odd it didn’t creak on the first test ride. 

In short, the crank arm is toast and needs replacing. The BB itself is in good condition and runs smoothly, so is perfectly reusable, but as Octalink is no longer common, finding replacement crank arms was an issue. Basically I could only find a new Alivio set which would be fine, but for the fact it wouldn’t add to the overall look of the bike. 

After a little cogitation, it dawned on me an alternative might be right under my nose…

Some time ago I rescued a binned Steppenwolf hardtail MTB frame with some components still attached, including XT cranks and a more modern external bearing BB. Why not see if it’s the same width as the octalink BB?

Lo and behold it was, so I would theoretically be able to replace a Deore LX crankset and Octalink BB with an XT crankset and modern external BB, at no cost. Not bad at all and 100% eco-friendly.

One problem. Don’t have the right tools! 

As systems evolved, so the tools needed to work on them change. Though this a consequence of welcome technological innovation, it poses something of a challenge for the home mechanic.

A regular crank extractor tool doesn’t work with an Octalink BB. To remove a BB on a vintage bike you need a hook spanner, an Octalink BB needs a BB removal nut thingy (like for a cassette but bigger), and an external BB uses another type of large spanner with slotted splines. Consequently, you often need different tools to work on various bikes. 

The bike shops near me aren’t really set up for the home mechanic, so buying tools is interesting and expensive. Apparently, in Switzerland, folks like to get other people’s hands grimy instead of their own (which probably makes sense).

As I quite enjoy grimy hands and torn knuckles I set about looking for tools and stumbled across a sale on Chain Reaction for an 18 piece toolset, for 50CHF delivered, including some tools I had already, everything I needed for this job plus a couple of extras. Pretty good deal, and arrived within a week. 

Once the package hit the doormat, like a child on Christmas morning I ripped it open and within 20mins had replaced and upgraded BB and crankset and chainrings to higher spec parts. Great!

The toolset is made by X-Tools, and though I was hesitant about quality given the price, I am quite pleased. 

The “new” drive train all works perfectly and it’s always most satisfying to complete an long term unfinished job.


So the moral of the story is, if you can salvage used parts, do so. You never know when you might need them and they’ve often got lots of life left.

Secondly, always invest in (quality) tools. Even if technology changes, and you only use them a few times, they pay for themselves quicker than you think.

Also, that which is new today will be vintage tomorrow, so there will always be more bikes to work on! 

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