What's the difference where a piston is between start of induction vs power stroke?

[H.G.P.]

Trying to visualize the difference in where the piston is at start or just before intake vs power stroke

1. At/start Intake-Induction (TDC?)

2. Compression

3. Spark-Power (TDC?)

4. Exhaust


What's the difference in where the piston is between #1 , just at or before induction begins, and #3 the spark power stroke?

Thanks

[bit]

No difference, except a 360 degree rotation in the crankshaft, but only a a 180 degree rotation in the cam shaft changing the valve orientation.
What did I win?

.Steven
1980 911SC

[real550A]

What's the difference in where the piston is between #1 , just at or before induction begins, and #3 the spark power stroke?

#1 Intake valve open. Piston, driven by crankshaft, causes vacuum.

#3 Valves closed. Piston forced down by compression/ignition drives crankshaft.


What did Steve win?

[H.G.P.]

Originally posted by bit
No difference, except a 360 degree rotation in the crankshaft, but only a a 180 degree rotation in the cam shaft changing the valve orientation.


.Steven
1980 911SC

So what I'm trying to visualize then, is then at TDC the difference is in the valves?

1. At TDC the all the valves are closed? (at the spark)

2. So after rotation both intake and exhaust are both open to the same/proportional degree, and the only difference then is in the size of the valves?

3. And also after rotation, intake and exhaust are taking place simultaneously?

Thanks

[911mot]

The camshaft rotates at half engine speed and it does not matter which TDC you use when installing cams.
When people say the timings 180 degrees out that refers to the distributor in relation to the camshaft position. (I.E sparking at the TDC for the exhaust/inlet overlap point instead of the TDC for the start of the power stroke.
If the distributor drive is via an offset slot, and driven of the crankshaft, then you might have to swap the leads 180 degrees to get the spark at the right TDC

hope this helps

[H.G.P.]

Originally posted by 911mot
...(I.E sparking at the TDC for the exhaust/inlet overlap point instead of the TDC for the start of the power stroke.
If the distributor drive is via an offset slot, and driven of the crankshaft, then you might have to swap the leads 180 degrees to get the spark at the right TDC

hope this helps

(I have a few more items (mainly tinware), before officially trying to start the engine.)

I have spark, but I'm not sure the difference between the valve "overlap" adjustment, and how that differs from the valves at #1 cylinder being closed for the power stroke.

I used Wayne's book, and the Haynes, and did the cam timing correct for the valve travel.

The distributor points at no. 1 spark plug wire in the distributor cap at TDC, and at TDC the rockers have the 0.1mm gap (rockers free to wiggle a little at #1), isn't this the power stroke as the valves are closed? (or are both valves going to be opened..how do I tell the difference and avoid dumping fuel and washing the cylinders?)

[H.G.P.]

Originally posted by H.G.P.
(I have a few more items (mainly tinware), before officially trying to start the engine.)

I have spark, but I'm not sure the difference between the valve "overlap" adjustment, and how that differs from the valves at #1 cylinder being closed for the power stroke.

I used Wayne's book, and the Haynes, and did the cam timing correct for the valve travel.

The distributor points at no. 1 spark plug wire in the distributor cap at TDC, and at TDC the rockers have the 0.1mm gap (rockers free to wiggle a little at #1), isn't this the power stroke as the valves are closed? (or are both valves going to be opened..how do I tell the difference and avoid dumping fuel and washing the cylinders?)

Additionally: I do have the timing marks on the flywheel also. So what ideally should I attempt to do at this point:

1. Peer down no.1 spark plug hole and look for the top of the piston when the pulley/flywheel is at Z1, and check that the points are:

a. Open?
b. Just starting to open?
c. other?

And

2. Check that the rockers have the small wiggle 0.1mm at this point?


Which direction (1969E coupe, Bosch dizzy) should I be rotating the dizzy housing to guarantee the spark takes place before the intake valve (if this is the difference) opens?

Will the intake valve open regardless of the intake or power stroke to the same degree? The only difference being there being a spark before the valve opening as opposed to the overlap?

Thanks

[lateapex911]

I don't know if this helps, but....

Different cams will affect valve opening and closing points. But that said, when a cylider is going to fire, both valves will be shut. An aggresive cam will close the intake valve later as the piston rises to TDC, but later or sooner, the valve will be closed by the time the piston reaches TDC.

Typically, "overlap" refers to both valves being open at the same time. This occurs at the end of the exhaust stroke, and the begininig of the intake stroke, and is done to aid cylinder filling at high revs.

So, just to be redundant, the piston starts at TDC, with both valves closed and the spark plug fires, the mixture burns, and the expansion forces the piston downward. As the piston nears the bottom, the exhaust valve begins to open, and the piston hits it's lowest point (BDC) then begins upward, forcing the burned gases out the exhaust valve and into the exhaust manifold, or header system. As the piston rises to TDC, the exhaust valve is closing, and the intake valve is opening. The downward sweep of the piston creates vacuum drawing in fresh gas mixture. At the second pass of BDC, the intake valve closes,, and the piston moves up, compressing the charge mixture. When it reaches the top (or some degree before, depending on revs), the spark lights and the cycle begins anew.
So, 4 cycles: power, exhaust, intake, and compression, each one being an upward or downward stroke of the piston.

Your distributor will point to the #1 wire post when the #1 cylinder has the piston at the top and the valves closed ...every time.

[H.G.P.]

OK. thanks.....I remember now that in the dial reading for the overlap I went 360 from the dots up positions. Intake opening.

So the following 360 the rockers loosen, valves closed. And here the distrib is pointing at the #1 so I think I'm ok.

So if I have:

1. Spark

2. Fuel

3. Timing (advanced best or retard ??)

4. Compression

5. Adequate starter torque


the engine starts, correct? Engine turns by hand currently OK. I'm not sure how much power from the starter I should be listening for though:

How fast will the starter rotate on a rebuild?

If the starter rotates, and a no start, which direction should I try to rotate the dizzy?

Finally, if the above no start, then I will use the compression gauge. (I can hear the wooshing of the cylinders on hand crank though, but if I need an antire new set of Ps and Cs so be it)

[Wil Ferch]

This might help...

look at caliber60's graph here:

http://forums.pelicanparts.com/show...ght=four+stroke


Wil Ferch

EDIT:
Can't seem to link properly....drill down to caliber60's graph here---->Stup Q of the Day - TDC???

[911mot]

[911mot]

this one has points

[DarrylD]

This one has MFI injection