TDC Cyl #1 for a 3-chain 996 (2004, 3.6L)

[Domiac]

UPDATE: When you touch IMSB, do not set your engine like described on this message, see the full thread, especially the last messages. This message and the picture show compression TDC #1, meaning cylinder #1 top dead centre, just after compression and before power stroke. Instead you need to find out overlap TDC #1, meaning cylinder #1 top dead centre, just after exhaust and before intake stroke. If you cannot inspect valves e.g. using a borescope (or simply don't want to be overcautious), once you can lock bank 1 camshafts with the specified tool, you should have overlap TDC #1.

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Once again I turn to renntech to get some help on my wonderful 996 journey :king:

See the pic and comment if I got TDC for #1 or not, thank you!

Textual description follows below..

At my current crank position, the following are true

1) TDC Zyl #1 mark is good, locking pin installed

2) All my camshafts cutouts (grooves) point vertical

3) Cyl #2 intake valves open, Cyl #3 exhaust valves open. Cyl #4 exhaust valve 1-2mm open (about to close), all other valves closed

4) My LN Engineering camshaft lock tool fits bank 2 but not on bank 1 (bearing + toolset ordered late 2013)

As the firing order is 1, 6, 2, 4, 3, 5 and thinking of my valve positions, I'd say I am on TDC for #1, would you agree?

Turning crank another 360 degrees should get me to TDC for cyl #4, also the camshafts would turn 180 degrees and cutouts (grooves) align again as vertical. However, as the camshaft cutouts (grooves) are not symmetrical, I wish to double check that I have understood this correctly. I am not able to find clear pictures on how to lock camshafts for a 3-chain engine, therefore I am hesitant to proceed with my IMS work.

Thanks again!

Edited April 14, 2014 by Domiac

[JFP in PA]

Another poster (Xmac) recently added this example of how the cam notches are off center and how to read the TDC positions :

[Domiac]

Yes, I've seen this image. It is exactly the Xmac's thread that puts me in doubt that I am off by 360 degrees. Bank 1's exhaust camshaft bore hole looks just like the middle image, smaller circle on the right side. Turning 360 would obviously mirror my camshafts. However, Xmac's 1999 car has a bit different engine, e.g. it has 5-chains whereas my engine has 3-chains + variocam.

Another variable is the camshaft locking tool itself as I am using LN Engineering's tool and not the original Porsche locking tools.

Weekend is coming. I'll continue having some r&r with my car on Friday and start it by rotating 360 degrees and try out LN Engineer's camshaft lock to bank 1.

[xmac]

No expert, but it looks like you are 360deg off. Can you post some higher resolution images of your bank 1 cams?

[Domiac]

No expert, but it looks like you are 360deg off. Can you post some higher resolution images of your bank 1 cams?

Sure, there you go: https://www.dropbox.com/sh/vd9i43skh9nifl6/p_KlLwJcMX

I am off 360, if I can trust that your engine works like mine (probably it does) when it comes to your image.

[JFP in PA]

Yes, I've seen this image. It is exactly the Xmac's thread that puts me in doubt that I am off by 360 degrees. Bank 1's exhaust camshaft bore hole looks just like the middle image, smaller circle on the right side. Turning 360 would obviously mirror my camshafts. However, Xmac's 1999 car has a bit different engine, e.g. it has 5-chains whereas my engine has 3-chains + variocam.

Another variable is the camshaft locking tool itself as I am using LN Engineering's tool and not the original Porsche locking tools.

Weekend is coming. I'll continue having some r&r with my car on Friday and start it by rotating 360 degrees and try out LN Engineer's camshaft lock to bank 1.

Looking at your latest pictures, I would concur; and remember to only rotate the engine clockwise, never counter clockwise.

[xmac]

TDC for a given bank will have a larger "half-moon" on the crankcase side and smaller on the valve cover side. Based the higher res pics with a pixel count, you are TDC cyl#4.

Bank2:

Bank1:

Edited April 10, 2014 by xmac

[Domiac]

Gentlemen, I stand corrected. Will do 360 tomorrow and write a closure here.

Yes, one should always turn crank clockwise only.

[Domiac]

Only thing I cannot figure out is that if I have TDC for Cyl #4 then why my valves are like this:

- Cyl #2 intake valves open

- Cyl #3 exhaust valves open

(- Cyl #4 exchaust valves open 1-2mm)

Now, the firing order is 1, 6, 2, 4, 3, 5. And if I'm TDC for Cyl #4 then

- #3 is going to TDC in 120 degrees but how could it as it is currently on exhaust?

- #2 has gone past TDC 120 degrees ago approaching BDC but why does it have intake open?

However, not sure how much intake/exhaust overlap. Have tried to find out specs from the web, not succeeded.

Thinking of the firing order, TDC for Cyl #1 sounds logical. But, I am more than likely wrong and I'll do the 360 tomorrow.

Edited April 12, 2014 by Domiac

[xmac]

Out of curiosity, can you pull out the intake cam plug on the other side of the bank to check if the single notch in the camshaft is pointing inboard (towards the crank) or outboard (towards the valve cover)? In the case of 5-chain TDC cyl#1, it would point outboard.

Not sure if 3-chain motors have this too as a way to double-check.

[Domiac]

Out of curiosity, can you pull out the intake cam plug on the other side of the bank to check if the single notch in the camshaft is pointing inboard (towards the crank) or outboard (towards the valve cover)? In the case of 5-chain TDC cyl#1, it would point outboard.

Not sure if 3-chain motors have this too as a way to double-check.

I have pulled out all four cam plugs out. All four camshaft bore holes notches are vertical (up/down).

My answer to you contained a dropbox link (https://www.dropbox.com/sh/vd9i43skh9nifl6/p_KlLwJcMX) that shows four images (bank 1 intake, bank 1 exhaust, bank 2 intake and bank 2 exhaust camshaft bore holes images). File names are visible bottom left on the dropbox UI. Notice that the shadow and close camera orientation makes the angle for bank 1 a bit weird (this is not exact science, but it might be a bit off still).

The real question is that if I am on TDC #4 right now, then it means that #2 is near bottom still just finishing power stroke, cylinder full of exhaust gasses. If so, then why #2 intake would be open at this very moment pushing gasses back into intake manifold when piston soon begins to go up?

I am beginning to wonder that is there another feasible way to verify this, DME needs to know this too :-)

Thanks guys!

Edited April 10, 2014 by Domiac

[Domiac]

Sorry, updated my previous message from "if I am on TDC #1 right now" into "if I am on TDC #4 right now", big difference..

Edited April 10, 2014 by Domiac

[Domiac]

xmac, for clarity, I added two more pics to dropbox, a combined shot of the camshaft bore holes for bank1 and another one for bank2. Once again this is a 3-chain engine.

Also, if anyone knows, I'd be really interested to undestand the following: If I am on TDC #4 right now, then it means that #2 is near bottom still just finishing power stroke, cylinder full of exhaust gasses. If so, then why #2 intake would be open at this very moment pushing gasses back into intake manifold when piston soon begins to go up?

:notworthy:

[xmac]

On the five chains, there are 6 cam plugs, 3 per bank, 2 on one side & one on the other. I believe on your engine the single is a bigger brown plug. If I pull the green plug on the intake cam next to the scavenge pump, I can see the notch where the reluctor ring is attached in the intake camshaft, if pointing outboard, tells you you are on cyl#1.

Borrowed a pic, showing the single green plug, (ignore the circled cam position sensor):

Upper middle of this picture shows the single notch in the intake cam:

I was just curious if the 3-chain engines provided a similar secondary verification of timing. I couldn't find a picture of an engine with the bigger brown plug removed.

[Domiac]

On the five chains, there are 6 cam plugs, 3 per bank, 2 on one side & one on the other. I believe on your engine the single is a bigger brown plug. If I pull the green plug on the intake cam next to the scavenge pump, I can see the notch where the reluctor ring is attached in the intake camshaft, if pointing outboard, tells you you are on cyl#1.

I was just curious if the 3-chain engines provided a similar secondary verification of timing. I couldn't find a picture of an engine with the bigger brown plug removed.

My 2004 3.6L 3-chain engine has only 2 green plugs on one side and 1 larger brown plug on the other side per each bank. This engine does not have the third opposite green plug per each bank as with 5-chain engines.

My thinking is that if I remove the brown plugs, I should gain the opposite access to my intake camshaft. Now I wonder where should the notch point at on a 3-chain engine for TDC #1. Have to check my manuals, only problem is that my Bentley seems to be mostly for 5-chain (all images at least) and WSM is definitely missing 3-chain.

Here's couple pics more of the opposite banks (dropbox has larger resolution), the look of 3-chain engines are quite different.

[Domiac]

Pulling the big brown plugs on my banks did not provide anything useful. They simply reveal camshaft sprockets but without any such markings that could help figuring out TDC for cylinder #1.

[Domiac]

Gentlemen, I beg to disagree.

I constructed a simple table that shows cylinder stages based on the firing order. See the attached image. Note, here I assume that TDC #1 is 0 degrees, in reality it might be something else but that is irrelevant.

I find it impossible that I was TDC #4, just see the table and remember that my valves were at 0 degrees like this:

- #2 intake valves open

- #3 exhaust valves open

Hence I must be TDC #1 because cylinder #6 is going TDC next, and then cylinder #2.

I decided to turn crank some more and it supports my feeling that I was indeed TDC #1.

At 0 degrees, results are the same what I stated on my first message

- #2 intake valves open

- #3 exhaust valves open

- matches perfectly with my table's 0 column

At 60 degrees, results are now:

- #2 intake valves closed

- #3 exhaust valves open

- #4 intake valves starting to open

- matches perfectly with my table's 60 column

At 120 degrees, results are now:

- #4 intake valves open

- #5 exhaust valves open

- matches perfectly with my table's 120 column

At 360 degrees, results are now:

- #6 exhaust valves open

- #5 intake valves open

- matches perfectly with my table's 360 column

So, in my opinion the content on my first message is correct. But now I have turned 360 degrees clockwise, I have TDC for Cyl #4.

LN Engineering camshaft lock tool does not fit either bank anymore. It might fit on bank 1 if I'd do 720 and carefully try to jam it in, it would be tight however that much I can see already.

Any help on this would be highly welcome! :help:

Edited April 12, 2014 by Domiac

[Domiac]

Let's assume I was on TDC #4 during 0 degrees. That means that I should have seen the following:

- intake #5 open

- exhaust #6 open

But that was not the case, instead I saw #2 intake and #3 exhaust open (my first message). This means that #2 is near bottom still just finishing power stroke, cylinder full of exhaust gasses. Why #2 intake would be open at this very moment (0 degrees) pushing gasses back into intake manifold when piston soon begins to go up?

To compare, here's another table which assumes TDC #4 during 0 degrees, which I feel is wrong.

Edited April 12, 2014 by Domiac

[Ahsai]

Domiac, your definition of TDC is TDC followed by spark immediately but TDC can also mean TDC followed by intake immediately ("UP" in your tables).

What if Porsche's TDC@1 equals your UP@1, then it seems everything is consistent? Basically in the first table, cyclic shift your color columns six columns to the right to align with your TDC definition.

Edited April 12, 2014 by Ahsai

[Domiac]

Domiac, your definition of TDC is TDC followed by spark immediately but TDC can also mean TDC followed by intake immediately ("UP" in your tables).

What if Porsche's TDC@1 equals your UP@1, then it seems everything is consistent? Basically in the first table, cyclic shift your color columns six columns to the right to align with your TDC definition.

Yes, then my valve and piston behaviour would be perfectly consistent. Actually I have given this a thought, but why would Porsche define TDC @ 1 in such way that cylinder #1 it is just coming into intake stroke and intake valve is just about to open? I'd think that "Putting TDC for cylinder #1" means that you find the top dead centre for cylinder #1 just after compression stroke and before power stroke, meaning the ignition is just about to happen and all valves are close before and after TDC.

Thanks a lot for the answer, I'd like to get some more people to support this theory.

Edited April 12, 2014 by Domiac

[Domiac]

To be clear, my original table is still a fact, that is how my valves and cylinders act when I turn my crank clockwise. Only question here is how Porsche defines TDC for Zyl #1.

Option 1) TDC for Zyl #1 means top dead centre for cylinder 1 which is about to ignite, if you move 0 - 120 degrees forward, still all valves are closed for cylinder 1. Same thing if one would move 0 - 120 degrees backwards (do not however do this), all valves are closed for cylinder 1.

Option 2) TDC for Zyl #1 means top dead centre for cylinder 1 which is about to come into intake stroke, if you move 10-120 degrees forward, you'll see that intake valve is open

See the attached image to this post, this table is assuming option 2 just like Ahsai explained on his message.

Now, if anyone know which one of these is proper, please let me know.

Thanks!

Edited April 12, 2014 by Domiac

[Ahsai]

Based on what you measured and post #7, seems only option 2 can make everything consistent? Although I must admit I would have thought Porsche define TDC using option 1 but your measurements showed otherwise.

Edited April 12, 2014 by Ahsai

[Domiac]

Based on what you measured, seems only option 2 can make everything consistent? Although I must admit I would have thought Porsche define TDC using option 1 but your measurements showed otherwise.

Option 2 is perfectly consistent for my 3-chain 996 engine. I have inspected carefully how the pistons and valves move for multiple times now.

I am wondering if option 1 is still valid and with 3-chain engines the bore hole circles are meant to be opposite when compared to a 5-chain engine. Then again, option 2 might be valid, I have failed to find information about this from all my sources.

I am at loss here :huh: and unable to proceed with my IMS change as I wish to be sure I have my cams in correct position before proceeding.

Please anyone, share your thoughts!

[Ahsai]

Questions

1) what are the cam dev readout on both banks? Should be very small based on your photos

2) can you put the LN locking tool on bank1 now? If not, if you rotate the crank 360, will the tool fit bank1?

[Domiac]

1. Durametric: Camshaft position deviations: 1,53 and 2,58

- but this was a measurement taken while car was idling (not with high RPMs) and this measurement was taken just before http://www.renntech.org/forums/topic/45550-cylinder-misfire-gasket-blown-inside-bore/ . Still, I doubt my paper journey has nothing to do with the issue at hand :-)

2. I cannot put LN locking tool to either banks anymore after I rotated 360. It _might_ go in bank 1 but it would require substantial violence (bending) to get it in by hand. That being said, it could be that if I turn 720 and retry inserting LN locking tool to bank 1, I might get it in with lesser amount of force.

Since my first message in this thread, I have already moved 360 and now I suspect I am on TDC #4 (definition option 1). I'll do another 719+ degrees tomorrow and see if I can fit LN tool finally to bank 1.

This must be a topic that interests other 3-chain engine owners upgrading their IMS, hopefully we get a proper closure at some point.

Thanks Ahsai!

Edited April 12, 2014 by Domiac