In short, here are some things I've come to believe about roller chain maintenance:
-regularly lubricating roller drive chains dramatically improves their longevity. In a perfect world, drive chains on a combine, silage chopper or other farm implement would be lubed daily. (This strategy is for high-speed chains on combines, choppers, etc. Slow-speed roller chains, like those that drive the seed meters on planters, live in a world of fine, abrasive dust, and seem to get along better if they're run "dry" except during storage.)
-my preference is to lube chains with a two-part chain lube just after the machine has been shut down for the day, when the chains are warm. "Two-part" chain lubes are thin and penetrate into the warm links easily when initially sprayed on the chain, then coagulate and form a thick protective film after a few minutes. The congealed lube clings to the chain and doesn't fling off and make a mess on the machine.
-any lubricant is better than no lubricant when it comes to (high-speed) roller chains. Some folks squirt used engine oil onto their roller chains, and they get along fine. It makes a huge mess on the combine when it gets slung off, but used engine oil or its equivalent is an adequate lubricant.
-It is as potentially harmful to run a roller chain too tight as it its to run it too loose. Excess tension increases wear to pins and side plates, increases the heat of the chain, and puts excessive side-load on bearings on any shafts driven by an over-tensioned chain.
-when installing a half-link in a roller chain, the narrow end of the half-link goes in the direction the chain will travel.
-when installing cotter keys to hold the side plate on a half-link or master link, there are two schools of thought: some advocate putting the head of the cotter key toward the direction of travel, so that momentum will always keep the cotter key in place should the "tails" of the cotter key become unfolded. Others advocate putting the "tails" of the cotter key toward the direction of travel so that anything that the chain encounters--the sides of idlers, grain, etc.--will keep the tails bent so the cotter key can't come out. In discussions with representatives of chain manufacturers, one rep told me to install cotter keys "head forward," and another rep told me to install cotter keys "tail forward." So perhaps it doesn't matter which way the cotter keys are installed.
Maybe I worry too much about small, inconsequential things. But then, the Space Shuttle blew up because an o-ring got out of position...