cam index notch orientation
03-22-2017, 07:48 AM
#1
6th Gear
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cam index notch orientation
Hi. I've had the heads off my '98 Boxster for a couple years and am finally putting it back together. While I've done a lot of reading regarding timing the cams, I often end up being just short of completely confident.
My question is about the orientation of the indexing notches on the
intake cams.
On bank 1- when #1 cylinder is at tdc compression, the index notch on the intake cam is pointing away from the engine....
.....then,
Where is the index notch pointing on the intake cam of bank 2. (meaning cylinder #4 is at tdc exhaust)
My question is about the orientation of the indexing notches on the
intake cams.
On bank 1- when #1 cylinder is at tdc compression, the index notch on the intake cam is pointing away from the engine....
.....then,
Where is the index notch pointing on the intake cam of bank 2. (meaning cylinder #4 is at tdc exhaust)
03-22-2017, 08:45 AM
#2
Rennlist Member
Both marks point in OR both point out, depending on whether you are at TDC or at TDC exhaust. Bentley's and 101 Projects books are not clear on this.
If you plan to pull off both sets of cams at the same time, I can recommend using the procedure outlined in Porsche 986 Boxster Workshop manuals available in electronic version.
If you plan to pull off both sets of cams at the same time, I can recommend using the procedure outlined in Porsche 986 Boxster Workshop manuals available in electronic version.
03-22-2017, 05:44 PM
#3
Rennlist Member
Hi. I've had the heads off my '98 Boxster for a couple years and am finally putting it back together. While I've done a lot of reading regarding timing the cams, I often end up being just short of completely confident.
My question is about the orientation of the indexing notches on the
intake cams.
On bank 1- when #1 cylinder is at tdc compression, the index notch on the intake cam is pointing away from the engine....
.....then,
Where is the index notch pointing on the intake cam of bank 2. (meaning cylinder #4 is at tdc exhaust)
My question is about the orientation of the indexing notches on the
intake cams.
On bank 1- when #1 cylinder is at tdc compression, the index notch on the intake cam is pointing away from the engine....
.....then,
Where is the index notch pointing on the intake cam of bank 2. (meaning cylinder #4 is at tdc exhaust)
Like this
03-22-2017, 08:41 PM
#4
Drifting
I agree this can be bewildering at first.
Have you found the great Thread by Insite that explains all this and has lots of photos?? see this for other useful links:
https://www.renntech.org/forums/topi...w-limit-value/
You were lucky to get BY to help you. His Inlet cam has no notch notch in the photo because the photo is at the Exhaust-cam-notch-end.The Inlet cam notch is at the opposite end of this Bank. I suggest you try this little exam to see if you really understand. I did it to check myself. It works.
Draw a diagram of where all the notches should be for each Bank at TDC compression #1 .The do it for other cylinders.
There are tricks. The notches for the Exhaust cams are not exact half moons.There is a small part of the 'half' moon and a large part.Call them 3/8 & 5/8 moons. Make sure you can see the difference and the correct side of the 'unequal half' moon is the correct side of the parting line between the cam cover and the cylinder head. Draw diagrams -it helps.
Note this example of some very smart guys getting quite confused and eventually figuring out the ambiguity for a 3 chain engine in a 996:
https://www.renntech.org/forums/topi...-996-2004-36l/
Modified from Post linked above:
"TDC #1, meaning cylinder #1 top dead center, compression stroke completed ,plug already fired,and power stroke about to begin. Instead you need to find out Overlap TDC #1, meaning cylinder #1 top dead center, 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"
The biggest problem doing this with the engine in place is access and visibility. To confirm the Inlet cam on Bank 1 is perfectly horizontal, you need to look straight/level at it. When you try this you will discover many parts obstructing your line of sight. I suggest a small,powerful LED Inspection light and use a smartphone camera on a selfie stick. This sounds silly only to those who are not currently working on this project. This is what the RennTech guys did in the link above.
The other point of confusion is terminology.If you don't have the terms and their difference crystal clear ,you will flounder (like many of us!) . For example: TDC compression or TDC exhaust/overlap. 5/8 'half' moon or 3/8 'half' moon .
To find the locking boss through the crankshaft pulley , use an awl to begin locating it. Then center it with a 5/16" stubby drill bit painted white(so you don't forget it is there when you close everything up!!) . Rotate the engine with a 24mm short socket and a breaker bar or ratchet (if the plugs are out) .Don't turn the engine backwards more than a few degrees. Draw diagrams of where all the notches are at both ends of both Banks . On the diagram, always show orienting details like the oil pumps. water pump to avoid confusion. Having the plugs out helps confirm TDC -use a stick and a borescope or whistle to determine compression/exhaust tdc Use the corrected color chart on Renntech to check your assumptions about piston positions. Extend it out to 720 degrees. Don't get confused between 996 and 986.
And most of all, share your links?
Have you found the great Thread by Insite that explains all this and has lots of photos?? see this for other useful links:
https://www.renntech.org/forums/topi...w-limit-value/
You were lucky to get BY to help you. His Inlet cam has no notch notch in the photo because the photo is at the Exhaust-cam-notch-end.The Inlet cam notch is at the opposite end of this Bank. I suggest you try this little exam to see if you really understand. I did it to check myself. It works.
Draw a diagram of where all the notches should be for each Bank at TDC compression #1 .The do it for other cylinders.
There are tricks. The notches for the Exhaust cams are not exact half moons.There is a small part of the 'half' moon and a large part.Call them 3/8 & 5/8 moons. Make sure you can see the difference and the correct side of the 'unequal half' moon is the correct side of the parting line between the cam cover and the cylinder head. Draw diagrams -it helps.
Note this example of some very smart guys getting quite confused and eventually figuring out the ambiguity for a 3 chain engine in a 996:
https://www.renntech.org/forums/topi...-996-2004-36l/
Modified from Post linked above:
"TDC #1, meaning cylinder #1 top dead center, compression stroke completed ,plug already fired,and power stroke about to begin. Instead you need to find out Overlap TDC #1, meaning cylinder #1 top dead center, 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"
The biggest problem doing this with the engine in place is access and visibility. To confirm the Inlet cam on Bank 1 is perfectly horizontal, you need to look straight/level at it. When you try this you will discover many parts obstructing your line of sight. I suggest a small,powerful LED Inspection light and use a smartphone camera on a selfie stick. This sounds silly only to those who are not currently working on this project. This is what the RennTech guys did in the link above.
The other point of confusion is terminology.If you don't have the terms and their difference crystal clear ,you will flounder (like many of us!) . For example: TDC compression or TDC exhaust/overlap. 5/8 'half' moon or 3/8 'half' moon .
To find the locking boss through the crankshaft pulley , use an awl to begin locating it. Then center it with a 5/16" stubby drill bit painted white(so you don't forget it is there when you close everything up!!) . Rotate the engine with a 24mm short socket and a breaker bar or ratchet (if the plugs are out) .Don't turn the engine backwards more than a few degrees. Draw diagrams of where all the notches are at both ends of both Banks . On the diagram, always show orienting details like the oil pumps. water pump to avoid confusion. Having the plugs out helps confirm TDC -use a stick and a borescope or whistle to determine compression/exhaust tdc Use the corrected color chart on Renntech to check your assumptions about piston positions. Extend it out to 720 degrees. Don't get confused between 996 and 986.
And most of all, share your links?
Last edited by Schnell Gelb; 03-24-2017 at 01:35 PM.
03-25-2017, 11:41 AM
#5
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Thanks so much for the wealth of information. Some of it has become familiar to me, although tdc overlap is a term I hadn't heard until now.
Schnell, your comment about confusion over terminology is well taken. I have been confused from the beginning of my mechanical endeavors with the term tdc. I've always known that any cylinder can be at top dead center, so, have often been scratching my head when a reference is made to tdc without specifying which cylinder. i have since come to assume that a reference to tdc without specifying a specific cylinder is always intended to mean cylinder #1. Do I have this correct?
Having read many of the posts, links, and service manual regarding timing; I am actually feeling like I understand much about the relationships between timing marks, cam positions, notch alignments....and so forth.
I'm at a point where I am installing the cams following a valve job. I have the cams in bank one installed, and am quite certain that everything is as should be. I'm getting ready to install the cams into bank two, and wanted to be sure that I have these cams in the correct orientation with regards to the bank one cams which are currently in the position for tdc compression.
New Art, I think your reply above has answered my question.
I really appreciate when folks like yourselves chime in. I have learned a lot thanks to this forum. Mostly, how little I know.
Schnell, your comment about confusion over terminology is well taken. I have been confused from the beginning of my mechanical endeavors with the term tdc. I've always known that any cylinder can be at top dead center, so, have often been scratching my head when a reference is made to tdc without specifying which cylinder. i have since come to assume that a reference to tdc without specifying a specific cylinder is always intended to mean cylinder #1. Do I have this correct?
Having read many of the posts, links, and service manual regarding timing; I am actually feeling like I understand much about the relationships between timing marks, cam positions, notch alignments....and so forth.
I'm at a point where I am installing the cams following a valve job. I have the cams in bank one installed, and am quite certain that everything is as should be. I'm getting ready to install the cams into bank two, and wanted to be sure that I have these cams in the correct orientation with regards to the bank one cams which are currently in the position for tdc compression.
New Art, I think your reply above has answered my question.
I really appreciate when folks like yourselves chime in. I have learned a lot thanks to this forum. Mostly, how little I know.
03-25-2017, 01:21 PM
#6
Drifting
Suggest you look on Youtube for "Boxster Camshaft Allocation." Glen has a good series on rebuilding a Boxster cylinder head.Pity he lost the music recently.
But you need that color chart I mentioned
Share all of it here with links so we are all on the same page.It would take far to long to describe it all just for this Post.
It is very easy to be either 180 degrees out or off by 1 tooth.The assurance that you are not making such very expensive mistakes is in the links I gave.
But you need that color chart I mentioned
Share all of it here with links so we are all on the same page.It would take far to long to describe it all just for this Post.
It is very easy to be either 180 degrees out or off by 1 tooth.The assurance that you are not making such very expensive mistakes is in the links I gave.