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At 3:30ish in this video, they set light to a front derailleur. Why? Degreasing it? Waxy lube that needs melting in? I can't think of a good reason. Any ideas?

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It looked cool and intentional, but it also looks like a really quick way to melt any bushings or plastic spacers in your FD. –  WTHarper Mar 10 '13 at 11:53
    
I have heard of setting light to disc pads, but they are designed to get hot... –  mattnz Mar 10 '13 at 20:14
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@mattnz one time I got oil on my disk pads. I threw both the pads and disks in a fire. The discs got cleaned up. The expensive pads crumbled immediately! –  Vorac Mar 18 '13 at 6:59
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@Vorac: Yeh, that would happen... What you do is pour a teaspoon of meths on them and set that on fire. The oil burns off without excessive heat. –  mattnz Mar 18 '13 at 20:37
    
@Vorac Were they 'Eco' type green pads? I've baked sintered pads in the oven and set them alight with alcohol, and never had crumbling. I'll be more careful now! –  Mere Development Mar 20 '13 at 7:09

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up vote 10 down vote accepted

Well I thought we needed an answer to this, so I just phoned the shop. He's a nice fellow (as you can tell from the vid) and said that his mechanic is convinced that this method works to free-up seized and corroded mechs. Apparently dousing it in something like GT85 and lighting it for a very short time boils in the lube, and works.

I assume that the combination of a penetrating lube, some heat, and vapour would achieve this as a last resort for badly seized metal components. I've done something similar on bearings when trying to get them out of BMX cups in the past.

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Heat is a good way to loosen metal-metal fittings (for bearing cups but also stuck seatposts, pedal spindles, and quill stems) but I would never recommend it if there was a chance of melting or deforming any of the plastic components on modern derailleurs (or of lighting yourself or your home on fire...the same reason using gasoline as a degreaser is foolish.) A safer option would be to use a heat gun. –  WTHarper Mar 14 '13 at 16:13
    
@WTHarper Yep I heartily agree! Care needed :) –  Mere Development Mar 14 '13 at 17:07
    
Good sleuthing on that question. –  WTHarper Mar 14 '13 at 18:19

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