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I'd help out if I was nearby, but unfortunately I'm not. Here's my method for timing the engine:

NOTE: rotate crankshaft at top of flywheel from intake side to exhaust side as looking from the top of the engine

1: with car in neutral, remove valve covers and remove cams (sorry if you've done it once already, but you should do it again anyways); this requires removing the cam sprockets prior to removing the cams; remove the timing tensioner (old style) or remove the 12mm nut from the end of the tensionser (new style); for later style, use a screwdriver to relieve the tensioner; if you don't understand this, just remove the tensioner entirely and then it will be obvious what I mean

2: remove the spark plugs

3: insert a plastic straw (like from a McDonalds drink) into the number 1 spark plug hole and note it's height; don't drop the straw into the cylinder head (perhaps you could tie a large knot in one end to make it larger than the sparkplug hole)

4: while having a friend hold onto the timing chain and allowing it to roll on the crankshaft, rotate the crank with the flywheel until you see the straw move all the way up and then start to go back into the cylinder; move the crank back and forth until you have determined the peak of the stroke and leave it there (TDC); keep in mind that your helper MUST keep the timing chain tight and feed chain into the crank sprocket while also recovering chain from the opposite side so that the timing chain does not get damaged while you rotate the crank; if this makes no sense, I'll clarify at your request

5: Install the camshafts with the timing mark as close to the proper location as possible so as not to damage the valves.

6: install the exhaust cam sprocket while pulling on the timing chain; it should be absolutely as tight as you can possibly make it; it should also be done without disturbing the crankshaft position (straw indicator) and maintaining the camshaft alignment with the timing mark

7: install the intake cam sprocket with no slack between it and the exhaust cam sprocket while not disturbing the position of the crankshaft (straw indicator), exhaust timing location; it should also properly align with the intake cam timing mark.

8: install the tensioner; later style should not have 12mm nut installed when installing tensioner and ratcheting tenshioner end should be retracted; after tension is installed in head, install 12mm bolt on later style to apply tension; early style just turns in and applys tension with oil pressure.

9: rotate crankshaft/camshaft to verify that the timing marks on the camshafts align when the straw indicator is at the peak (or as close as possible) of it's stroke; be sure that both cams are aligning with the timing marks; remove tensioner and retime if you are off by a tooth

10: once satisfied that the timing is properly aligning after rotating crankshaft several times, install sparkplug in cylinder 1, torque cam bolts to spec, then install vavle cover.

11: start engine and check distributor timing with timing light


There is enough difference between one tooth and another than you should be able to determine if you are timed properly. If you are off one tooth, the straw indicator will be lower one way or the other. Properly timed, the cam marks should line up pretty well whether you are a little before or a little after TDC on the crankshaft. As you move the crank a little back and forth, the straw should bounce up and down a little while the cam timing is pretty much right on the tick. If the straw is going down any significant amount, you are off by a tooth and need to correct it. The timing chain should always be tight on the exhaust side when installing the sprockets, then the tensioner takes up the slack on the intake side.
 

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Stop using the flywheel timing marks and do it exactly as I said with the straw. I suspect you are rotating the crank while trying to take the slack out. With the straw, you'll be able to visually check that piston 1 is at TDC while you get the cam sprockets on. Also, remember that it is critical to do the exhaust side first since there should be no slack on that side.

The little black ring is the o-ring, but it sounds as if it's hardened considerably. Just go to Napa or where ever and pick up a new o-ring.
 

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I'm pretty sure its not the o-ring.


About the TDC:
There is a dead zone where you are rotating the crank and the piston doesn't move. Besides, how could the flywheel mark be inaccurate?
The piston DOES move and if you used the straw you would see every detail of how it is moving while you perform the work. I think it is difficult to know if you have moved the crankshaft inadvertently using the flywheel to determine TDC. You also must turn the engine over several times by hand to verify that the timing is in fact correct. This tensions the chain fully and allows you to figure out how many teeth you are off.

If you rotate the engine and find the exhaust cam is not all the way to the timing mark, then you know you need to move the sprocket by at least a tooth toward the exhaust side of the head. Mark the chain and the sprocket with a sharpie so you know how far you have moved the sprocket, then rotate the engine again to verify the timing. If you're still short of the timing mark, move it another tooth. Once you have the exhaust side timed properly, fix the intake side making sure the chain is tight between the 2. Rotate the engine and verify that both cams are lining up with the timing marks.
 
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