TDC confusion need help...

[ertech]

Hi guys
Put my engine back together rocker cover and all, my crank at z1
Look at my rotor on distributor and it is facing #4, I am sure I installed it facing #1 . I was thinking when I was aligning it the rotor must has turned but not sure . Is there a way to make sure I put the rotor in the right place facing the # 1 notch and pulley at z1

To make this clear it I align the z1 notch how do I make sure I am on firing of #1 and not #4?
Thanks
Erick

[Mitch1]

Could you turn it 360 degrees and check where distributor rotor is pointing?

[ertech]

At this point I don't know where I am. How do I start from scratch?
Thanks

[Ronnie's.930]

Originally Posted by ertech

At this point I don't know where I am. How do I start from scratch?
Thanks

What you need to do is this - put the crank pulley on Z1 (are you certain you know which mark that is?), and make sure that piston #1 is on top dead center of the compression stroke . . . if it is, check to see where the rotor is pointing . . . if not pointing at the notch (cylinder #1 on distributor cap) then you will need to remove the distributor and reposition the shaft.

To check for #1 TDC you are going to have to either remove the valve cover and watch to see if the intake valve goes from closing to fully closed as you approach the Z1 mark or put a small wooden rod in the spark plug hole and watch as the piston moves it upward (but that won't guarantee that it is on the compression stroke).

[HawgRyder]

The wooden dowel method is good if you put your finger over the plug hole first as the piston moves upward to see if it's making compression.
When the piston does finally reach TDC in that way...you are at the #1 position to fire.
Bob

[ertech]

3-questions
1- if as the piston goes up , if it makes compression than it is on the stroke that fires?
2- how do I reach with my finger?
3-If I am not on the fire stroke( opposite on the crank by 360 )there should be no compression as piston goes up?
Can I,
A-pull spark plug #4
B-put a compression tester in the spark hole
C-turn the crank as I approach z1 if I get compression. Than my rotor should line up with number 4 spark plug wire( there is more room on #4 side)



Thanks
Erick

[mreid]

If your valve covers are installed, I assume your valve are adjusted. Remove the driver side valve covers and wiggle both the intake and exhaust rockers on #1 cylinder. If they are slightly loose, you are at TDC. Assuming. They aren't, rotate the engine one revolution and check again. Now they will be and you are at TDC on the compression stroke of #1 and the dizzy is now pointing to #1.

[Ronnie's.930]

1) - yes as the only other time the piston goes up is the exhaust stroke and the exhaust valve is fully open at TDC of the exhaust stroke.

2) - doesn't seem possible with a 911 head . . . looking at the valve/rocker action is much easier.

3) - I guess I don't quite understand why you are asking about cylinder #4?

[ertech]

Isn't my way easier than removing both valve covers?
A - remove spark plug #4
B-put a compression tester in the spark hole
C-turn the crank as I approach z1 if I get compression. Than my rotor should line up with number 4 spark plug wire( there is more room on #4 side)

Thanks

[ertech]

Cyl 4 spark plug is easier to reach than number 1
If I see compression on 4 as the mark gets to z1 than I can align the rotor to point at number 4 if I don't feel compression than I align the rotor to point at #1
Does this work?

[Ronnie's.930]

Erick, you might as well give that a try and see what you get. Personally, I wouldn't even bother with removing a spark plug, and would instead remove the left side, intake rocker cover and watch the #1 intake rocker.

[ertech]

Sorry for being slow
If I remove the left intake cover , what will this tell me?
Should the intake valve be closed ( will be able to wiggle the rocker)on the compression and exhaust stroke?I still won't be able to tell .right?
Thanks

[DSPTurtle]

The rockers will only be loose on the compression stroke. If the rocker is loose, then you are at the correct spot. As for #4, yes it is easier access and all of your logic makes perfect sense but there is no mark on the dizzy like there is for #1 so it is a bit more guesswork. You could always just fire it up and if it doesn't start move the dizzy 180 degrees. That's a hack way of doing it but btdt and it was fine. Didn't do it on purpose though. Lol

[Flat6pac]

Amen on the rocker...
Bruce

[ertech]

isn't the intake rocker lose< valve closed >on both the compression and exhaust stroke so the exhaust gazes don't go to the intake on exhaust stroke.
this is confusing

[Ronnie's.930]

Hello Erick, no doubt it can be confusing. It took me quite a bit of time and experience checking/adjusting the valve lash (primarily on on Ducati engines) before I could basically take any four stroke engine and find the various TDC in about two seconds (takes practice and maybe making some mistakes along the way).

You don't really need to be concerned about the "loose factor" of the intake valve/rocker - all you need to do is slowly spin the crank pulley and watch that the #1 intake rocker moves from the open to the closed position and check the location of the Z1 mark and the distributor rotor while you are doing so.

[Ronnie's.930]

Originally Posted by ertech

isn't the intake rocker lose< valve closed >on both the compression and exhaust stroke so the exhaust gazes don't go to the intake on exhaust stroke.
this is confusing

No - at that point (exhaust stroke) the intake lobe on the cam is beginning to ramp up and some tension will be on the rocker (the valve will still be closed, however).

[Ronnie's.930]

Originally Posted by ertech

If I remove the left intake cover , what will this tell me?

It will allow you to watch the movement of the #1 intake rocker as you spin the crankshaft.

[lindy 911]

1. Put a wrench on your crank pulley bolt.
2. Pull the top valve cover off the #1 cylinder side.
3. Turn the crank with said wrench until you see the intake rocker on #1 push the valve down.
4. When the valve starts to come back up (close), watch the pulley for the Z-1 mark and line up with case joint (straight up).
5. You are now at TDC.
6. Pull dizzy and reinsert with rotor pointed at the notch.

[ertech]

Thus is what I did
Removed the # 4 plug
Put my compression tester in
As I approached z1 the #4 cylinder was building pressure so I assumed I was on #4 compression, my rotor was pointing at 1
Past the z1 and rotated a full 360 to z1 no pressure buildup on 4
Took dist off and lined up the rotor to the mark pointing at 1
Thanks all for your help

Does this look right?