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Originally Posted by insite
what makes you think that? i understand the process fairly well, but i've never timed one of these.
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Well, the first thing I would do is visually check if the chain did slip a tooth or not. If you put the engine at TDC, and the slot on the cam is parallel to the line of the head/ valve cover joint, you can be fairly certain it's in time (in your picture, it is not parallel, so if the crank pulley is at TDC you are likely off one tooth). If you pull off the oil extraction pump (take note of its orientation, as they use the same part for both banks, but in different orientation) in the head, you'll see a chainwheel, which is bolted to the exhaust cam by 4 10mm bolts. The chainwheel has slots to allow for adjustment. The intake cam (as I'm sure you know) is driven off the exhaust cam via a separate chain and this contains the VarioCam tensioner. So, if the timing is off on the exhaust, it is also off on the intake. The timing mark, which the timing tool fits into, is on the intake cam. The tool merely holds the cam stationary while bolted to the head.
Hypothetically, if the chain slipped one tooth, you could be able to remove the tensioner and move the chain over one tooth the other way and be done (you'd need the valve cover off for this) but I've never tried doing this. However, to actually time the engine, you must loosen those 4 10mm fasteners, and do the procedure. I would roll the engine over and check both sides if you get stuck doing this. The tool only fits into the cam one way, so if it won't fit on bank 1-3, it would fit into bank 4-6, so if you are timing bank 1-3, you'd have to roll the engine over a turn. When timing the whole engine, you time one bank, then roll the engine 360, then time the other. I then roll the engine several times and double check things. For a 5 chain motor, you do need the auxiliary tensioners, which place a precise amount of tension on the chains. Supposedly you can time a newer, 3 chain motor without these, but you do need the tensioners on a 5 chain motor.
The 10mm bolts holding the chainwheel to the exhaust cam should be in the middle of their adjustment range, so you should have plenty of range to move either way during the timing process. The easiest way of re-timing your one bank would be to move the crank until you can fit the timing tool into that side's cam, lock the tool down, loosen the adjustment bolts on the cam, then roll the engine backward and then forward (to take any potential slack out of the chain) until you hit TDC (you only want to move forward when coming up to TDC), lock the crank with the fixing pin, and then tighten the 4 10mm fasteners (10 pound torque if I remember). Then, roll the engine 2 full revolutions, and re-check.
Like I said, if you get stuck doing this, I would check both banks while you have the engine out of the car and it's pretty easy to do.
Personally, I find the way you time these to be very imprecise, as there is potential variation in way too many places (where the TDC mark is on the pulley, variation in machining those slots into the non driven side of the cam during manufacturing, variation in tolerances in the tool, etc) but short of figuring out "true" TDC with a dial gauge on piston 1 or 4, and knowing the overlap numbers, it is what it is.