I found what I was thinking of and have two different examples which you are basically doing the same thing. This should get me really close to TDC.
Quote:
1. Make an indicator from some clear plastic tubing, a jar of light oil, and an old sparkplug.
2. Break up an old sparkplug and attach a length of clear plastic tubing to it (make it airtight).
3. Remove all the spark plugs.
4. Stick your thumb OVER the #1 cylinder spark plug hole. Rotate the engine (see note below on tricks for this) until you feel pressure on your thumb. That's the compression stroke. TDC is at the top of this stroke.
5. Screw in the sparkplug with plastic tubing attached and insert the other end of the tube into a jar of light oil. Continue rotating the engine. Bubbles will appear until the piston reaches the top of its travel. When it starts down on the next stroke, the bubbles will stop and oil will begin traveling up the tube. Stop at a convenient point and mark the tube. Then mark the crank pulley and the engine body at a convenient spot.
6. Rotate the engine backwards and watch the oil recede into the jar. Continue rotating. As the piston continues past tdc and downward it will again suck oil into the tube. Rotate the engine till the oil again reaches the mark. STOP! Mark the crankshaft pulley where it lines up with the mark you made previously on the engine. You should now have two marks on the crankshaft pulley. The midpoint of these two marks lined up with the mark on the engine is tdc. Whoa! Almost like finding South with a wristwatch. Boy and girl scouts listen up.
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and this one
Quote:
Take an old spark plug and remove the guts (porcelain and middle electrode), then create an internal thread through the middle of the hollow spark plug or weld a nut (about 5/16 or 8mm) to the spark plug shell so you can thread a long bolt through it. Now install this new TDC tool into No. 1 cylinder (with bolt backed off).
This procedure works best if the chains are off. Loosen the rocker arm adjusters fully (you don't want to introduce valve head to piston), as you will rotate the engine around without the valves in synch.
Install the crank pulley and rotate the engine (CC or CCW) so the crank pulley TDC notch is about 1/2" or so from the TDC line on the crankcase (for No. 1 cylinder). Thread the bolt in by hand until the bolt stops against the piston. A nut snugged on the bolt helps hold this position. Place a temporary mark on the pulley opposite the TDC mark on the crankcase. Now rotate the engine (by hand) again in the opposite direction. As you approach TDC, slow down, then gently continue until the piston stops against the TDC bolt. You'll feel the resistance. STOP and again mark the pulley opposite the TDC mark on the crankcase. You now have two marks on the pulley. True, absolute TDC is exactly halfway between the two marks. Repeat as often as you like to validate. If halfway between marks happens to land on the factory notch, great. If not, create a new notch as this is your new TDC reference point for accurate cam and ignition timing. Paint it with white paint for visibility and don't forget to remove your TDC tool.
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any comments are more then welcome.