So after much abuse, the chain on my KFX50 broke at the master link and I have a couple of questions:

1. What is the rubber part that it hit (in red square)?
2. Is this cup-looking washer a standard part I can buy at a hardware store or something I have to contact the dealer about?
3. It looks like the chain is a 428 pitch with 76 links. Can I use a 78 link chain and adjust the tension or do I need to get a chain breaker to remove 2 links?
4. Looks like the roller on one of the ends of the chain has some scratches. Is it okay to reuse the old chain with the scratched roller or should I get a new one?

 

I don't know that model, but:-
!. The rubber thing will be to protect the swinging arm pivot tube from the chain rubbing against it as the suspension goes up and down. From the dirt on it, I would guess the chain hasn't been hitting it much.
2. Can't make out what that is in your picture.
3. If fitting a new chain, adjust the tensioners as short as possible, put the chain on, and see how many links you need to remove. It could be the old chain had stretched and someone has removed a link to take up the slack, so new chain needs to have more links.
4. Only you can decide if the damage to the old chain means it requires replacement. However check it for stretch. There are several ways to do this, the sideways "droop" test being the most common, but a bit subjective. The put chain round the rear sprocket, pull away at the middle and check for daylight test, indicates pass or fail, but I find all but the newest chain will fail that test. I'm sure both tests will be up on U Tube.

 

Thanks for the reply!

Yeah, the rubber part has never been touched by the chain until it snapped. The washer looks like a cup. You can actually see it in the first picture where it secures the rubber part, but this one was from the other side that got hit by the chain. Sounds like I can just grind down the damaged area and reinstall.

 

So, I finally replaced the chain.

The extra 2 links were not a problem as there was plenty of adjustment on the chain tensioner.