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BASIC ENGINE TESTING Four Stroke Cycle Intake stroke Piston going down intake valve open Low pressure created in cylinder Volumetric Efficiency maximum at w o t Compression stroke Piston going up both valves closed Mixture squeezed to increase combustibility molecules raises temp Needs good seal to compress and combust Power stroke Piston going down both valves closed Work is performed by expanding gasses Exhaust stroke Piston going up exhaust valve open Exhaust gasses exit Any exhaust left over dilutes incoming a f mixture with inert gas exhaust Causes poor quality and quantity of charge Valves Valves serve two purposes Sealing during compression and power strokes Opening up of ports during intake and exhaust strokes Cylinder Sealing Performed by tight seal of valve face against seat to seal in compression pressures Most common loss of compression is valve not sealing properly Broken Valve Spring Valve not fully closed Bent Valve Bent due to piston contact Burned Valve Face burnt due to poor contact with seat leaking Proper Valve Seat Position Guide Seat Face Opening of Valves Controlled directly or indirectly by camshaft Volumetric Efficiency Three factors affect VE How far the valve opens lift The amount of time that it is open duration Size of opening A problem with valve opening will affect volumetric efficiency or the quantity of incoming fuel mixture Multiple valves Multiple valve heads will act same as big valve heads Secondary throttle plates can be used to eliminate loss of ram effect Lobe Lift Duration Lift How far valve will open Duration How long it stays open Head Design Wedge style most common cost effective design Hemi style very efficient air flow expensive Porting polishing increases air flow less restriction reduced turbulence in ports Carbon Buildup Carbon build up on intake valve Worn valve guide seal oil Fuel deposits Affects V E Flat cams Valve doesn t open fully Testing Vacuum gauge testing Provides quick test for compression problems Should

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