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