RE: YS 160 DZ
Putting oil in the cam gear area...is only because when the motor is new or has set in a box for a while and this area may be dry. When its dry the first start up can cause some damage before the motor gets up to temperature and oil starts to migrate to the cam area via the normal path.
Just so that you know....Oil drips down from the valve cover area through the pushrod tubes. Now the pump side of the DZ pushrod tubes is pretty tight as the pump has a piston that sort of seals it up. Some fuel, oil can come in the bottom of this pumps piston and will drip down into the cam. The exhaust valve pushrod is the biggest and easiest way for the oil to get down there. It then drips through a little hole in the bottom of the lifters that ride on the cam. From this little hole it enters the cam gear area. SO by sticking a little oil in there before you run the motor the result is you insure the cam gear is protected.
On the first start of the motor if this is dry perhaps you can get a little un-needed wear and the result is 30-50-100-150 flights later the cam can fail. Also running the motor out fuel can cause this un-needed wear as the motor can backfire and this causes problems. But that is another topic for another time.
I started doing the oil thing on the cam many years ago when I had a cam fail on a new 140L at about 50 flights. I started thinking about what was going on and have not had a cam failure since. I do this on all my YS motors when they are new, or I have taken them apart for checkup or repair. By the way I also put oil inside the case to lube the piston, rod and crank on the first run also.
Makes them a little harder to start on the first run out of the box....but for the most part oil is protecting the metal to metal contact points.
Troy