The timing can be changed from the exterior of the engine on the basis of {HEAD ~ factors} such as the quantity and nature of pollutants in the exhaust gases, {TAIL ~ the rate} of revolution of the engine and the load on the engine 
The timing can be changed from the exterior of the engine on the basis of { HEAD ~ factors } such as the quantity and nature of pollutants in the exhaust gases , { TAIL ~ the rate } of revolution of the engine and the load on the engine
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH