I have some questions about my 1975 XS650B. When I pulled the engine and began to drain the oil I noticed some metal shavings. When I took the oil filter out of the right side cover it also had some metal shavings. Where could this come from? I would also like to know a couple things about valves. One of the exhuast valves is bent, but the rest look to be ok. Would I be able to replace just the one valve or should I go for all of them? Is the guide(or guides) in need of replacement ? Do all xs650 years have the same valves or did they change with year and model. Could I order replacement valves from a Yamaha dealer?