4 Stroke and Top Dead Center

[plowjockey]

Having an impossible time positioning a distributor in a 97 Nissan V6.

Two questions.

1. Assuming the heads were removed, is there any difference between the exhaust and compression stokes, concerning the physical rotation of the crankshaft?

2. When i detect the compression stroke, I rotate the balancer to the furthermost left timing mark (as per instructions). However if i put a screwdriver or straw in the #1 cyl, if I continue to turn the crank, they will rise another inch (at least) showing me that the piston is not all the way up. shouldn't it already be at the very top? If i rotate the crank 360 degrees the result is about the same.

[bigjon]

tdc-is when the piston just reaches the top of its stroke,with both valves closed.is your Nissan a twin cam engine?

[StL.Ed]

Originally Posted by plowjockey

Having an impossible time positioning a distributor in a 97 Nissan V6.

Two questions.

1. Assuming the heads were removed, is there any difference between the exhaust and compression stokes, concerning the physical rotation of the crankshaft?

2. When i detect the compression stroke, I rotate the balancer to the furthermost left timing mark (as per instructions). However if i put a screwdriver or straw in the #1 cyl, if I continue to turn the crank, they will rise another inch (at least) showing me that the piston is not all the way up. shouldn't it already be at the very top? If i rotate the crank 360 degrees the result is about the same.

1. For the crankshaft and pistons, TDC happens twice, once on the exhaust stroke, and once on the compression stroke, so the position would be the same on both cycles; the camshaft, valves, etc. are different because the camshaft turns once for each two rotations of the crankshaft. The timing chain keeps the two in proper sync.

2. The timing marks will normally be before TDC. How many degrees of rotation are there between the timing mark and TDC?
The spark needs to fire far enough in advance to start the fuel burn before compression is complete. (Correct timing is normally expressed as number of degrees before TDC.)

ETA: Also, make sure you are checking the correct cylinder for setting timing...

Is that timing mark you're using supposed to be top dead center or where the timing is supposed to be set with the engine running ? Every vehicle I've ever timed had a TDC mark that had to be lined up when installing the distributor with the rotor button pointing at # 1 wire in the distributor cap . Also the engine needs to be on the compression stroke .
After installing the distributor in this manner a timing light is used to turn the distributor to the correct timing mark with the engine running . If the heads were off is it possible the crankshaft & camshaft wasn't properly timed when the timing chain was installed ?