May I add to Pablos solution to,
Throw out the Chinese ball bearing. If you are able to get it out, in most cases it is not perfectly round and low quality and may sometimes jam up the mechanisms.
Sometimes if the bearing is stuck, use the small extention tips that comes in most spray cans, CRC for example and spray in there. If that don't work, use spray can of degreaser, that will soften the grease that's holding the bearing , and usually it will fall out.
Extreme case , use compressed air to blow out the bearing cos I have had a few become sqauashed up and almost in a state of disintegration.
Replace with same size ball bearing from bearing retail place. Take the Chinese bearing with you ofcourse so they can size it up. Get some spares.
Prior to fitting the new bearing, add lots of hi temperature grease, molly grease is probably best. Grease up the cam and everything else.
Push the bearing in, then push in the pin, the excess grease will come out, and use that excess for wiping it around on the small 10 tooth sprocket.
