If you look closely a the master link keeper of your motorcycle chain, you'll see that one side has sharp edges and the other side is rounded, just like a flat washer. When the die stamps out the part, the process creates that rounded edge on impact. We always assumed that the rounded side should face up when you install the keeper. Not so.
That slight rounding side on the master link keeper makes it easier for the keep to come out of the slot that is supposed to hold it in place. Also make absolutely certain that the top plate is pushed down as far as it will go to expose the slot, and be careful that no dirt or dust comes between the link keeper and the master link. Otherwise, the master chain link keeper will never be really securely mounted.
While we're talking about master links of your motorcycle chain, remember that the keeper is not a reusable part. The master link keeper is made of spring steel and is usually distorted by the removal process. It can also be damaged by sloppy installation. Never lift on side of the keeper over the pin. Instead, push it on evenly. We know we don't have to remind you that the closed side face forward. If, for some strange reason, you have more that one master link, it would be very easy to install the chain with one of the master links facing the wrong direction and never notice.
Motorcycles in Southeast-Asian countries and Western countries wear out the drive chains in different ways. In climates with moisture, like Thailand, it's more common to have kinked links. This causes way more drag than a O-ring motorcycle chain could ever create. Even if you get the kinks out temporarily, they will come back, so it's time for replacement. In dry areas, chain stretch is a good indicator of wear. Once the chain can be lifted out of the teeth at the three o'clock position, it's done. The motorcycle chain will rapidly destroy a brand-new sprocket at that point. You can also measure it against a new chain of the same number of links. It should be no more than four percent longer.