I routinely use WD40 to clean my chain, and then I wipe it clean with one of the cats. Since cats are self-cleaning, I always have a fresh one ready to use. As an additional benefit, the WE40 prevents hairballs.
(And before anyone has a snit - no - I do not actually do this! It's satire, my boy, satire.)
Of all the articles (and blogs) I've read warning me not to use WD40, I am yet to read one which provides any sort of conclusive proof that WD40 does any harm to a chain.
WD40 is a lubricant. It says so on their web-page.
It's got lots of other uses, which makes it a very versatile solvent (water displacement, cleaning, rust-prevention, ant-seize, etc.) It is made up of roughly 50% mineral oil (think kerosene) and around 15% light machine oil, like sewing machine oil. Put some on your finger and it feels slippery...
Arguments have been made that WD40 is a degreaser, and therefore bad for chains, but this distorts the facts.
The high content of mineral oil means it makes a good chain cleaner, but that's only on first application. The more volatile components soon vaporise, leaving the lubricating components behind. It will keep your parts moving just fine for a very long time.
A specialised chain lube may possibly be superior, but for general use, there's nothing wrong with the WD40. Many bike shops get stroppy with customers who choose to use a cheap substitute for their ultra expensive (profitable?) teflon superlubes, but they have a vested interest, don't they?
My father's been using the stuff for decades, with no ill effects. He's well aware that it should stay out of internal components which are greased--which is true of any thin oil.
The reason it works on chains is it cleans them so very well, which is the most important part of chain maintenance. Bicycle chains operate under very low heat and pressure (from an engineering standpoint), so their lubrication needs are minimal. A completely dry chain will run quite well, until it gets wet and rusts. In fact, I've seen chains ruined more quickly from over-lubing, without any cleaning, which results in a chain coated in a slurry of grit and oil.
I only use it as a cleaner personally, and it is great for that. Someone on the BOB list once ran some through a mass spectrometer, and he came up with a formulation similar to what Toff described.
I recall where my father got the idea for using WD for his chains--it was a maintenance clinic hosted by a bike shop back in the '70s, when WD was fairly fresh on the scene. At the time, it was widely considered good chain lube, and nobody's chains were disintegrating.
The bike shop histrionics over the stuff are misplaced. Sure, WD can be misused. It will wreck a freehub body, and if you blow it into your hubs you'll be grinding bearings in no time. But it won't kill the external parts of your drivetrain.
I once pulled up to a trailhead, only to find the trail under six inches of fresh snow. There was a can of WD (which, incidentally, stands for "water displacement", and this is the forieth formulation) in the boot of my car, which Dad had left there. I hosed the drivetrain down, and I had a wonderful, freeze-free ride.
Like I said, I don't use WD-40 on my chain, as I realize there are better, longer-lasting options. However, I also don't believe the anti-WD folks have much experience using it properly either. They've just seen the results of ham-handed home mechanics misusing it. Happy Trails, Ron Georg Moab
...it was always my understanding that it worked fine for chains for both cleaning & lubing but that due to that light oil content, it had to be used regularly, ie:- before every ride... ...& i rode thousands of miles w/out incident on wd-40'd chains, back in the ' 70's...
...now, of course, i use the new 'super' lubes which do such an obviously superior job (at an obviously higher price) that i'm positive i've become better looking, more intelligent & quite possibly, i should be riding in the 'pro' peleton... ...ed w...please, loan me a cat...
As for cats and bikesgonewild, I can't loan you one, but I can certainly GIVE you one! She-Who-Must-Be-Obeyed rescued 4 feral kittens that we've been gentling. Three of them are fairly tame, but they still have some fear of humans at times. The fourth one was the last to be caught, and she's still very wary of people. Give her a couple of weeks here in Kitty Disney Land, and she'll come around.