I have a 2007 660 Rhino. Most times the starter engages and starts the engine normally. Occasionally the starter motor will stall. I think it engages because I can hear some sounds. But the engine doesn't turn over. The starter stalls. I let off the key and try again. Sometimes it will go on the second or third try. But sometimes it still stalls. During all this, I think my battery is OK. I really think the problem is in the starter motor. Could there some kind of compression release that fails to open? I recalled from the Car Talk radio show that Click and Clack described how a faulty starter motor can sometimes be made to run by tapping on the casing. So I tried that with an 18" ratchet extension. To my surprise, there was a small spark at the end of the extension, and the starter motor turned, engaged and started the engine! So, What Is Going ON?? Is the compression a red herring? Or is the spark a red herring?