Had my quad in the Silver Lake Dunes last weekend and kept hearing an awful clunking sound from the quad in the rear, took apart the sprocket today and checked rear bearings and all that fun stuff, then I noticed on one of the chain links, looks like the roller is missing. can I replace just that link/remove it? or do I need a whole new chain? the chain itnt very old and in good shape as are the sprockets.

2003 Scrambler 500 4x4

 

At one time at the shop we carried half links,but a lot of times when you loose a roller the chain is damaged. I've even see people add several links and end up having two master links,but not the best idea. Check a local shop if your chain doesn't appear to be damaged and see if thy carry half links.Not the best way imo,but if you're on a budget maybe you can salvage the chain. OPT

 

You can buy a chain breaker to remove the defective link or grind/file the end(s) of the pins off then drive the pin(s) out and add a master link or half link but as OPT suggested it may not be the best idea for something which takes the abuse your chain does. Compared to replacing a damaged sprocket or two from a not so perfect chain or getting stranded may make replacing the chain a bargain. There are a few Utube video's on chain repair available. BTW, I'd have no qualms about fixing the chain on a bicycle or other relatively slow moving chain particularly where I could easily keep an eye on it.