im probably gonna get ridiculed for this, but both me and CE were wondering this...i told him what i thought, but, maybe the ones of you are more experienced(Roundman, MD, etc) can help us out........what exactly does a cam do ?? i thought it opened the valves and what not and controlled the air flow as to how much got into the piston chamber to mix with the fuel.....if im wrong, PLEEZ correct me, cuz we were both wondering like i said, and its been buggin me. any help would be appreciated. thankx guys(and/or girls).

Zeke

 

I think and I could be wrong, that it let the gas and air in ( on my car),It holds the it in when the piston is go up, and then it let the old air out. I don't tell it very well so add to it.

 

the camshaft is the heart of any engine. it controls the movement of the intake and exhaust valves in a precise relationship to the crankshaft of the engine. the camshaft turns at 1/2 the speed of the crankshaft. the lobes on the cam operate the valves via the lifters, pushrods, and rocker arms. the valve springs that hold the valves closed put pressure on the rockers, pushrods, and lifters so that the lifter stays in constant contact with the cam lobes and follows the lobe as the cam rotates. when the lifter is on the base circle of the cam, the valve is closed. as the lobe shape increases, the valve begins to open until it reaches a maximum lift as the lifter goes over the nose of the lobe and begins to descend the back side of the lobe. as it descends, the valve closes until the lifter is back on the base circle of the cam. this opening/closing of the valve is done in a precise timing relationship with the postion of the piston in the cylinder bore to ensure the valves and pistons don't hit each other as they move up and down. this relationship is determined by the grind of the camshaft lobes and the angular relationship between them and the piston as it moves up and down in the cylinder and also how it is installed in relation to the crankshaft. the timing gears and chain between the crank and cam maintain this mechanical relationship between the two at all times so that all the movements are synchronized to each other at all times. these positions are measured in degrees of rotation of the crankshaft and are referred to as the valve timing. when the piston is at the exact top of the stroke in the cylinder, this is called TOP DEAD CENTER (TDC) and when the piston is at the exact bottom of the stroke, this is called BOTTOM DEAD CENTER (BDC). Describing the 4 stroke combustion cycle using the cam and piston postions, it works like this. on the intake stroke, the piston is moving down from TDC, the exhaust valve is closing but still open some and the intake is opening. this period when both the intake and exhaust are open is referred to as valve overlap and is a critical design factor in all camshafts since it affects how well the air/fuel mixture can flow into the cylinder as the piston moves downward in the cylinder. as the piston moves downward in the cylinder, the exhaust valve fully closes and the intake opens fully at max lift and begins to close. at BDC, both valves are fully closed and the piston moves upward on the compression stroke with both closed to build pressure in the cylinder prior to the spark plug firing to start the combustion process. for the most efficient combustion and power, the spark plug fires before the piston reaches TDC (BTDC) since it takes time for the mixture to begin to burn. both valves remain closed during the power stroke as the piston moves back toward BDC. as the piston approaches BDC, the exhaust valve just begins to open and it opens fully after the piston passes BDC and moves up pushing the burnt gases out of the cylinder. before the piston reaches TDC, with the exhaust valve closing but still somewhat open, the intake valve starts to open again. the reversion pressures in the exhaust system helps to draw the fresh air/fuel mixture into the cylinder as the intake opens while the exhaust is closing during the overlap period. then the cycle repeats. the cam shaft controls all this motion so that the engine makes power. the critical cam specs include the maximum lift for both the intake and exhaust valves, the offset lobe angle between the centerline of the intake and exhaust lobes on the cam, and the duration in cranskshaft degrees of rotation when each is is open, most often measured at 0.050" of lift. The shape of the cam lobe, the type of lifter used, the weight of the moving valvetrain components and the valve spring pressures are all critical factors that determine how well a particular camshaft grind will work in the engine.
Sorry if this is a bit long, but you asked the question and I tried to give you a decent answer so you would better understand how it works.[sm=imsorry.gif][sm=icon_rtfm.gif][sm=exactly.gif]

 

the cam controlls the vavles, wich allow air and fuel into the combustion chambers thru the intkae vavles, then allows the burnt exaust out the exaust vavles. the cam is ground to let in and out a certian flow equals the lift, the speed that the valves open and close is duration, the seperation is the amount between the opening and closing of the of the intake and exaust valves, to the best of my knowlege and ability to explain stuff.

 

ok, so in other words, i was pretty much right, just, not as technical as you all got....right ??? thanks for the technical part Roundman. i knew either you or MD would come thru for me and whats the "rtfm" mean ???

 

I don't know much about engines at all, and that made total sense to me. Like Grn N Gry said earlier, we were wonderin how all this worked... and now it makes sense. Appreciate the explanation Roundman (& socalstang) [sm=smiley20.gif]

 

whats the "rtfm" mean ???
read the f**king manual
don't feel bad, I didn't know what it meant until just the other day and I had to ask too!

 

i thought it meant read the ford manual

 

I guess it could, but then again it wouldn't be generic and apply to other makes or manuals that way! ha, ha

 

i thought the new smileys were something amanda made.