Posted by Keith in Washington on Tuesday, August 17, 2004 at 0:01AM :
In Reply to: Keith, you got me... posted by wally on Monday, August 16, 2004 at 8:11PM :
Your are still 180 degrees out on your thinkin. Top Dead center is when the piston is at its highest point on the firing stroke. Prior to firing near TDC The air fuel mixture must be compressed so both valves are closed. As it passes TDC the exploding air gas mixture is expanding rapidly which applies a lot of force to the piston to drive it down. This is the power stroke. Again both valves are closed until the piston is near the bottom of the stroke or all power would be lost out the open valve. The ehaust valve opens near to bottom of the power strok as the exhaust will be expelled out on the next up stroke.
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