Quote:
Originally posted by Doug Zielke
Now do this to find out......
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Doug,
Your procedure will
NOT work, at least not to determine if the spark plug is firing when cylinder 1 is at TDC ignition. I see there is a lot of confusion on this. Let me see if I can explain it clearly:
The 911 engine is a four-stroke engine and it takes
TWO full revolutions of the crank for any cylinder to complete its cycle. The cycle is: intake, compression, ignition, and exhaust.
The cams run at half the speed of the crank, and they determine what phase of operation a particular cylinder is in at any particular time.
So, if your rotate your engine to the Z1 mark, you're at one of
TWO possible conditions: Either cylinder 1 is at TDC with both valves closed, ready to fire (TDC ignition), or cylinder 1 is at TDC with both valves slightly open, preparing to intake charge (TDC overlap). If cylinder 1 is at TDC ignition, then cylinder 4 is at TDC overlap. If cylinder 1 is at TDC overlap, then cylinder 4 is at TDC ignition. That's why you have to look at the rockers to tell whether you're at the correct Z1. If they're loose, you're at TDC ignition on cylinder 1 and you can install the distributor with the rotor aimed at the rough timing mark. If the rockers are not loose, you need to rotate the engine one full revolution.
So, the cams, not the crank, determine what phase of engine operation you're in. Then based on that, the distributor can be timed to match.
KC:
Yes, since you set the cam timing and that's what determines where the distributor needs to be, I think it's very likely that the distributor is 180 degrees off.
-zuff