Grinding the bastards down

Grease on screw threads prior to inserting in bicycle bottom bracket

As reported in my earlier posts Mechanical prep for a long ride and A couple of discoveries, following some upgrades to Kuroko I had two screws that were too long. In the first case, the screw holding the cable guide onto the bottom bracket was interfering with the new crankset, and in the second the screw that fixes the pannier rack to the rear dropout was preventing the chain from moving on and off the smallest sprocket.

I thought briefly about asking to the use the custodian’s workshop at my office to file down the screws, but I quickly realized I could fit a small vise onto the storage box I keep all my bike goodies in. So I got a very small vise and set of files from Amazon, for a lot less money than I expected.

Diamond file setMini vise
Diamond files and mini vise

The files were probably a mistake. A wider file would have made it easier to work on the screws without slipping off (and potentially damaging the threads), and a coarser file would have made shorter work of the job. As it was I feel like I was progressing up to several microns per minute. The good news is that the result was a very fine powder of metal drifting down onto the vise which I was able to blow or brush away and not have to worry further about. (It’s probably in my lungs now, right? It’s in my lungs, isn’t it? Oh, dear … )

Filing the end of a screw held in a vise
Slow progress with the diamond file

I’d started with visions of taking five or 10 minutes to grind about 5mm off the end of each screw. After more than 20 minutes of work (including breaks to stretch my legs) and multiple trial fittings, I declared myself done with the first screw when it fit snugly into place without interfering with the spinning of the crankset.

The offending screwCable guide screw in place
Cable guide screw before and after the filing

I have to confess that with each trial fitting, I was worried about cross-threading the screw and damaging the bike frame — particularly as I was just filing the screw flat and then dressing the end a bit, not taking care that the threads ended in a nice taper. But the screw went into the bottom bracket cleanly, and I added a bit of grease. I hope it won’t rust as much now as it had been previously.

Using a hex key to measure the protruding screw on a bicycleStacked hex keys to measure the progress
Using hex keys to measure the progress

The pannier rack screw in particular was hard to thread in for fitting. It wasn’t until I’d reached this point that it occurred to me that an extra washer would be an easier solution to the problem. I checked among my leftover bits, but I didn’t have another washer of the appropriate size. Keep filing! I’m happy to report that the rack screw was a bit softer than the cable guide screw and so the filing went a bit more quickly. (This almost made up for the rounded head on the screw, which made it harder to secure in the vise.) According to my hex key measurement method, I needed to get about 4mm to make the screw flush with the frame eyelet. But in the end I took off just enough to make sure the chain could move on and off the smallest cog without any interference. Another dab of grease and a last fight to thread the screw into the eyelet without cross-threading, and I was done.

Protruding screw vs chainPannier rack screw protruding from eyelet next to bicycle sprocket
Pannier rack screw before and after filing

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