After power washing my bike several times this winter to get the road muck off, I've developed creaks in a few places.
What's the best way to clean and lube my bottom bracket, crank arms and seatpost? Do I need to take anything apart, or can I just spray lube on these places?
Yes, repeated power washing can blow the lubricant out of bike components and leave them dry and squeaky. First, always make sure when power washing a bike that you don't blast it into any bearings.
The best technique is to do as much spraying as possible in the plane of the bike, rather than from the side. So blast down from above, up from below (except not at the headset) and from the front and back. I understand that sometimes cleanliness requires some blasting from the side, and if it is just at the frame, no harm done. But blasting into jockey wheels, bottom brackets, pedals, and hub bearings is a bad idea.
Now, addressing your creaks associated with power washing, the first thing you should always do after washing a bike, whether with a power washer or a hose or bucket, is remove the seatpost and turn the bike upside down to let the water drain out of the seat tube. Do this after every ride in the rain as well.
It's a good idea to have a hole in the bottom of your bottom bracket shell to drain it while upright as well. If your bike does not have one, consider drilling one as close as possible to the very bottom—generally right up against the plastic cable guide screwed into your shell. That answers your question about the seatpost as well; remove it, grease it, and re-insert it.
Often the creaking is the leather at the edge of the saddle shell rubbing on the saddle rail clamp when your weight brings the two into contact. When the leather dries out, this rubbing will result in creaking, so applying grease to the edge of the saddle shell there can fix your problem.
Obviously, after power washing, lube your chain every time (actually, do it after every ride) and jockey wheels after every few times. The chain is a place for the spray lube you mention; on other parts it will have a transient benefit at best. With cartridge-bearing jockey wheels, pry the dust cover off of the bearing with a razor blade and squeeze some grease in there before replacing the dust cover.
Creaking in the crank and bottom bracket area is often coming from around the bearings. With a threaded bottom bracket, unscrewing the cups, greasing the threads, and tightening them back in to full torque spec will often fix it; plumber's tape on the threads of a persistent creaker might help too.
With a press-in bottom bracket, you may need to remove the cartridge bearings, put grease around them, and push them back in.
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