Selador wrote:When the #1 cylinder is at the top of it's travel, so is the #4 cylinder.
But only one of them is ready to fire.
Both are at TDC, but one's at the top of its compression
stroke, and the other's at the top of its exhaust
Piston #4 is at TDC at the top of its compression stroke, and at the top of its exhaust stroke, but how do you know which is which, when it comes to timing? YOU don’t, but the camshaft does: when the timing marks are lined up, THAT’S TDC of #4’s compression
stroke (which also happens to be TDC of piston #1's exhaust stroke). That’s just the way Isuzu designed it. Why they did it that way when most other vehicles use cylinder #1 as a reference, who knows: maybe it facilitated assembly line speed. You COULD take it upon yourself to modify the markings such that they correspond to the position of the piston in cylinder #1, but why bother, now that you know the 4ZE1 bases them on cylinder #4?