in a piston port engine,the exhaust port oopens the same number of degrees BTDC as it closes ATDC?

Question

true or false

Answer 1

Correct.. there is only a minute difference due to clearances measured in thousands...ie.. piston pin, and rod pin clearances..

Answer 2

Yes and NO
In most cases the timing is symetrical.
It can be adjusted by a few degrees if the cylindert is moved forwards or backwards in relation to the crank centre line due to the connecting rod angularity being different on compression or exhaust stroke. This can cause other problems as the angle con-rod makes will change thrust angle of piston to cylinder.
Its easier to visualise with a drawing at about 90 degrees before and after top dead centre. The piston moves up or down cylinder but the connecting rod angle forces it against front or rear of cylinder. Most wear occurs on thrust face (usually rear of cylinder)

Answer 3

Actually the exhaust is still open when fuel is entering the compression chamber, as it's being pushed in from the transfer ports. Some of the new unburnt fuel is blown out of the exhaust port before that port is fully closed. The back pressure created by the expansion chamber (exhaust pipe), pushes that unburnt fuel back into the compression chamber before the exhaust port is closed. That unburnt fuel is forced into the compression chamber, creating an overfilled condition. The additional fuel causes a higher explosion of the fuel/air mixture adding to the power the engine puts out.

Answer 4

yes