4 stroke engins

HEAD
 the head of the engin holds alot of important componets needed for the combustion process. the head has intake and exhaust ports wich are uesd to feed fuel and air into the boar for compression and exhaust ports wich connect to the exhaust manifold to remove waste fumes after combustion. inorder to let air/fuel and exaust in and out of the engin valves are needed to open and close to seperate and deliver presices amount of mixture for combustion. the valves open and close by being pushed open by a push road system wich has rockers or a rotaing camshaft with cam lobes shaped like a triangle with rounded corners.the cams are driven off the crank shaft by a belt or chain. ensureing the timing of the valves is esensual as valves out of time can cause majoir damage to engin parts.

HEAD CONPONETS

cams: cams are a very important part to a head and the engin. the purpose of the cam is to push down  on the cam bucets to compress the valve spring and open the valve or to push a push rod up into a rocker so the rocker pushes down on the valve to open it. the lobes on the cam are used to open the valves. the lobes are rounded and triangle shape so the valves open and close smothly and not  cause as much wear to the valves or cam buckets. the cams are atached to a cog on either on the out side of the engin or the inside depending on weither its driven by a belt or cahin. the belt or chain then conects to the pulley on the crank so that the valves open at the corret time of the piston stroke. on the cam we messure the cam lobes ,wear and bend in the cam. the cams were between the manifactures specs and were still uesable if the engin was to run again.

VALVE SPRINGS
the purpose of a valve spring is to return the valve after its being compressed either by the cam or rocker. with out a valve spring the valves would stay open and the engin would not run, also the valves could bend causeing damage to the valve seal, piston and sevral other engin conponets. valve springs can come in diffrent materails for special conditions such as titanium for high performance. in our practical we  checked to see if the springs were squar incase they mite be slightly bent witch could indercated further problems. the most the springs were out were .2 mm. we then messured the length of the springs with a vernier to check the length against manifactures specs .  all the valve lengths were between the manifactures specs. we check the length and squarness to ensure that the springs are still doing there job and do not have exstesive wear. short valve springs  may cause less resitance when valve returning or mean extensive wear has taking place. we checked the spring tensioner  to ensure they were compreesing to the right length acording to manifactures spec. doing this can idicated if the valve springs are worn and need replacing to resolve a problem.

VALVES
valves are used to let in air and fuel for combustion and to let out exhaust fumes. some head shave sevral valves per cylinder for more flow there for more power. valves sit in a valve seat wich hold the valve in but still let it have a smoth flow for when the cam or rocker pushes the valve open. the valves  have valve springs locaters seals to seal the spring and on cam shaft  heads have a cam bucket . this set up helps the valve to open and close when needed. in our practical we  messure the valve seats , thickness of valves and inspected the valve for damage or corrosion. all the valves ahd small wear but were still in usable condition and fitted well in the valve seats.

OVERALL HEAD INSPECTION
 overall the head was in a fiarly good condition. most of the componets were within the manifactures specs and only had small wear. although there were a few cam lobes  and springs that were a little over the manifacture specs. the condition of the haed was avrage. it had small warpage. scratches and a tiny bit of chiping on the outside. when assemberling the head  i had to time the cams together and check valve clearences with a fealer gage to manifactur specs. to do the valve clearinces i would have to replace the pads on the valve bucket. the bolts and threads on the head were fine and only a few bolts were missing before pulling apart. bolts were torquid down to half the manifacutres specs as the engin has being pulled about hundreds of times.