The cam shafts on either side of the engine work together to manipulate the intake and exhaust valves. On both sides only one is driven by the timing belt that rides on the cam sprocket that is bolted to the cam shaft. On each side of the engine, the cam shaft that does not have a sprocket pulley on it is turned by a pair of gears, one on each cam shaft.
Since only one on each side actually needs a cam shaft sproclet-pulley on it, no cam shaft seal is required, hence they cap that one off on the front of the engine with a "Cam Cap". The same on both sides, located near the cam shaft sprocket.
For more in the life of a "Cam Cap", just ask!!!
Hope this helps,
Keith
