To amplify what GTJIM said a bit, the 4-cylinder engine's #1 and #4 cylinders are "paired", as are the #2 and #3, so they are always at exactly the same position during their revolution, just "180 out" as far as ignition timing is concerned (one's firing at TDC, the other fires at TDC on the next crank revolution). The complete "cycle" of any "four stroke" engine requires TWO revolutions of the crank.Originally Posted by GTJIM
All engine "timing" is done in relation to crankshaft position. Almost ALL engines "share" cam timing and initial #1 cylinder ignition timing settings, the Opel CIH engine DOES NOT! Therein lies the confusion that sometimes baffles even experienced mechanics, at least initially. Some, who don't take the trouble to look at the valves, never get this.
Easiest way to remember CIH "timing" from scratch is to:
Set both crank key and cam dowel pin to 12 O'Clock position. This positions #1 and #4 pistons at TDC and also positions the cam to allow plug-side head bolt installation and torquing. The ignition "timing" is for the #4 cylinder however, NOT the #1 cylinder as in almost all other engines. Your choice, either leave it and time the ignition for the #4 cylinder or rotate crank ONE full revolution and time it for the #1 cylinder. Makes NO difference!!