up

 

From TDC with lobes out:
Intake cam open as piston draws down - allowing air and fuel to enter the cylinder.
Intake cam closes and piston starts to rise creating compression.
At about 5 degrees BTDC ignition fires spark and fuel / air mix ignites.
Piston is forced down (all valves closed.)
Exhaust cam opens exhaust valves after BDC and closing at about TDC
(Start again from top.)

What Bigger is describing is if you were to set the cam lobes in at TDC (180 degrees off from how they should be set.)

He was thinking that's what we were talking about (which I understand how he thought that.)

What we meant was that there are TWO TDC's and does it matter which one you set up the cams properly on (with lobes out.)

As they say, a picture is worth a 1000 words - So, check this out.

 

Is this statement true?

At TDC the Cams are pointing out, then rotate the crank one full revolution. The crank is again at TDC but the Cams are now pointing towards each other.

Is that true or false?

 

That is a false statement. You must remember that it takes 3 times longer to move around the "back" of the cam then it does across the LOBE.!!!!!!!

WHen setting you cams correctly you the lobes will be facing out(every knows this right) The piston in at TDC,and at the END of the 4th stroke(valves shut) AND the begining of the 1st stroke(TDC) . The "PEAKS" of the lobes will be at 3 O'clock(intake) and 9 O'clock(exhaust)



Moving clockwise........ [ 6 O'clock represents valve being OPEN)


TIMING MARK on the cranks (again end of 4th stroke/begining of 1st) INTAKE 3:00 Exhaust 9:00 SPARK!!!!!!But nothing to ignite.



1st stroke -INTAKE STROKE (intake) 6 O'clock (exhaust) 10:30 O'clock (piston at Bottom) ....intake opening,and shutting....

2nd stroke -COMPRESSION STROKE (intake) 9 O'clock (exhaust) 1 )'clock .......valves closed....

(valves closed TDC) 180 degrees out... SPARK!!!!!!!!! BOOOOOM!!!!

3rd stroke- POWER STROKE (Intake) 10:30 O'clock (exhaust) 3 O'clock ....valves still closed....

4th Stroke- EXAUST STROKE (intake) 1 O'clock (exhaust) 6 O'clock .......exhaust opening and shutting....



TIMIMG MARKS agian Cycle starts over. SPARK!!!!! But nothing to Ignite.



This is my best effort to make it understandable, maybe someone can explain it better.


[img]i/expressions/face-icon-small-blush.gif[/img][img]i/expressions/face-icon-small-smile.gif[/img]

 

biggerisbetter and DuneMe I appreciate your help.

Got another question...

If the piston is locked at TDC between the Compression stroke and the Power stroke will the timing marks on the Cams line up correctly? I understand the lobes of the cams will not be at the correct position, but will the timing marks still line up?

 

Haven't checked but, I would think so.

Yeh, Bigger is right about the lobe position. I think my statements are more of a general nature about the lobe positions. The marks on the cam sprockets are a much more accurate way of looking at things.

 

Since the Sprockets are directly attached to the Cams, the timing marks would not line-up between the compression stroke and the Power stroke. Each cam/sprocket makes 1 full rotation every 4 strokes.




bigger.

 

But, the marks should be horizontal again with the valve cover surface after one crank rotation the same way they were with the lobes out.

 

I think thats true if you are going by the other set of marks. But I dont believe you can set your valve clearances when using those marks, cause the cams will be in two different positions.



Bigger.

 

Hopefully this will be my final question on this drawn out thread! Once again thank your for all your help.

Here is a scenario:
Crank is locked at TDC with the TDC bolt, both cam sprocket timing marks line up with the arrows on the black plastic part in the middle. With out looking at the orientation of what direction the lobes of the cams were at, the cams were removed. The crank is still locked at TDC. Now for installation of the cams how do you know what orientation the lobes should be? Obviously the cam timing marks need to line up, but it is possible to line up the cam timing marks where the cam lobes are facing out or rotate them 180*.