Originally Posted by lancerman

Sorry I didnt explain it clearly. wasted spark doesnt happen at BDC. It happens at TDC at the end of exhaust stroke. its not burn gasses being expelled but an ignitable mixture since there was a mis fire (no fire) . The exhaust stroke doesnt empty cylinder completely and at top of exhaust stroke there is enough fuel/air to be ignited. as piston goes down on intake stroke more ignitable gas/air enters chamber. but it enters into a chamber that is burning. The piston is traveling down bore on intake stroke but the mixture entering chamber is burning at same time. there is no exhaust valve open this round when the piston is traveling back up bore. it is now compression stroke time. the hot expanded gases are very hard to compress. the piston end pushes rod down on its end and crank is pushing up from other side . rod is very easy to bend like this. pre ignition is far more damaging then detonation. it happens much quicker and is harder to detect because there will be no knock noise. detonation happens when pistons are at or very near TDC. the crank pin is not in a position to be rotated so the compression usually lifts head and blows gasket. when that happens there is no real stress on the rod. it is in its strongest position and the lifting head releases the excessive compression. pistons get hurt and rod bearing get beat on but rods survive just fine. hope that clears it up a little better for you.