It's always a great idea to keep your bike -- and particularly the drive train -- as clean as possible, but it needs to be done correctly.
Although many of the bikes we service are pretty clean (which is good), we've found that sometimes when the forks and bottom bracket are removed, there's a large amount of water present (which is bad).
So you've decided to clean your bike. Excellent! What do you need?
Cover your seat with at least two shopping bags. Saddles absorb a huge amount of water and can take a looooong time (days, if not weeks) to dry properly. Make sure to cover the headset bearings as well as the area where the seat post enters the frame.
Now get your bike up against a wall/tree or in your bike stand, then gently hose the dirt and sludge off.
Note: be careful when spraying water around the bottom bracket and hubs. Don't try to blast water past the seals.
Remove all the bags/plastic except for the ones covering your saddle.
Get a bucket of warm, soapy water and wash your bike from end to end. Use a sponge for the frame, wheels and cranks. A rag and bottle brush are great for the derailleurs and brakes. Don't overload your rag or sponge as this increases the chances of filling your frame with water.
Once you're done, hose off the soap using a fine mist.
Bounce your bike on its tyres several times to help remove excess water.
Mark your saddle height with a zip tie or tape, then remove the seat and post from the frame and put them in a sunny spot.
With a clean dry rag or towel, dry the bike as best you can. Take this time to inspect the frame welds and components for cracks and/or signs of wear.
Give the bike a final bounce to make sure there's no water trapped in the hollows.
Next, rotate the frame to see if there's any water inside. Turn the bike upside-down. Is there water coming out of the seat tube? Then you'll need to be a bit less aggressive with the hose next time.
Keep rotating and shaking the frame until it's water-free.
Now leave it in a warm and/or sunny spot for as long as possible to help the rest of the water evaporate and reduce the chances of corrosion-related problems.
If, once it's dry, your drive train is looking pretty clean, finish off by lubing your chain. If it's not looking clean, check this out.
You can also lube your cables if need be, plus check your brake pads. (It's amazing how quickly they'll wear in the wet.)
Your bike is now clean and, most importantly, dry both inside and out!
Go and have a celebratory beer.