Boz:

Pictures are a little newer engine with a complete rocker box, but still close.

The rear cover just pries off - an o-ring snaps in a groove to hold it.

When the cover is off you will see a slotted head screw that holds the camshaft in the bearing. Be advised, this screw is a LEFT hand thread. If you break it you'll probably never get a replacement, be careful.

Bill.