Camshaft Timing/durametric Reading/errors

[Dharn55]

Still trying to figure out if there is really anything wrong with the setting/timing of my cams after fixing my intermix problems. When I first checked the cam timing with my Durametric it was showing the following readings:

Camshaft position 1 deviation -10.86

Camshaft position 2 deviation -02.14

So I have been assuming that the bank 1 cam might be pretty far off. I ran the Durametric on my buddies car and the readings for these are about -1 to -2.

I had borrowed a cam position tool from another member and went to check/reset the cam timing today. But visually, there is no way it appears to be off by -10 degrees.

Based on this I did not reset the cam timing but decided to run the Durametric again and now get the following readings:

Camshaft position 1 deviation -12.15

Camshaft position 2 deviation -02.45

Actual angle for camshaft bank 1 .1 (at idle) 25.94 (at 2,000 RPM)

Actual angle for camshaft bank 2 .3 (at idle) 24.74 (at 2,000 RPM)

The actual angles vary a little bit with the engine running, but you can see the advance kick in between 1,500-2,000 RPM.

So here is my question. Do the camshaft position deviation numbers mean that the bank 1 camshaft is starting at -12.15, and then advancing 25 degrees so that it is at 13 degrees advance? Not really sure how to interpret these readings. But it sure dons not look like the bank 1 cam is off by 12+ degrees with the engine off.

Any help would be appreciated.

[snorth54]

I have no more information on the readings, however I can share the information Durametric provided for my 2004 911 Anniversary Edition with the Variocams.

I just updated the IMS bearing and was checking the camshaft position after the work was completed.

The camshaft position 1 deviation is always 1.28 regardless of RPM

The camshaft position 2 deviation is always -0-09 regardless of RPM

At 3522 RPM the Spec angle for inlet camshaft bank 1 is -40 and the Spec angle for camshaft bank 2 is -40

At 3522 RPM the Actual angle for inlet camshaft bank 1 is -39.65 and the Spec angle for camshaft bank 2 is -40.12

The Actual and Spec angles follow each other through the different speeds but are not tied only to the RPM. My understanding is the timing is contantly adjusted depending on engine requiring low end torque or fuel economy depending on a variety of inputs from the throttle position along with engine temperature (for warm up), etc.

[txhokie4life]

Just a guess here -- but could it be possible that while the exhaust cam is in alignment -- N/S to the valve cover,

that somehow the intake is slightly off as if when the cams were put back in the intake was off a tooth or two?

I'd don't know how to figure that out with out some disassembly

Could you swap cam position sensors and just make sure one is not reading funky?

mike

[Dharn55]

First I want to thanks those of you have have given me input.

Snorth54 - The varioCam on my 2000 is quite different from the VarioCamPlus on your 2003. If you are interested in the details of the systems check out this post I did a couple of months ago.

The short and the quick of it is that the early system is much simpler, with the exhaust cam timing fixed and a fairly simple RPM based advance of the intake cam relative to the exhaust cam by a fixed 25 degrees. On the newer engine the advance of the intake cam is variable based on a "vane" systems at the drive fo rthe intake cam and a much more complicated ECU control based on RPM, load and other factors. There is also a special lifter that changes to amount of lift on the intake valves. So all in all they are very different systems. Still thanks for your thoughts on this.

txhokie4life -That is a good thought. I was very careful in reassembling the cams, etc. but this could explain why the timing of the cams could be off. The timing of the cams is set by grooves on the end of the exhaust cam while the sensor is on the end of the intake cam. So if I did miss a link that would explain why the exhaust cam shows the timing correct yet the sensors are showing a deviation. Of course the challenge here is that I will have to pull of the cam cover on that side to determine if that is the source of the error, kind of a pain, but it is doable with the engine in the car. Might give it a try next week. Thanks for the idea and I will keep you posted.

[Dharn55]

txhokie4life - I was just looking at an extra set of cams, chains and advancers that I have and I think you my be right on. IF I was even off by one roller, not even one full link, this would be about the degrees I am off by. And one roller would be pretty easy to miss by. May go back in today and see if this is the case.

[Dharn55]

OK, so I am pretty convinced that I might have been off by one tooth in the chain between the cams. I was careful, but this is the most plausible explanation of the problem. So I figure 4-5 hours and I can have the cam cover off, check the allocation, and if necessary pull the cams, correct the problem and have it back together. 45 minutes later I have the car up on jack stands, the rear wheels off, the bumper off, the shields and the muffler off on the drivers side.

Then in looking closely I realize that there is no way to get off the upper bolts on the muffler bracket, or really get at the upper bolts on the cam cover without dropping the engine at least 5-6 inches. And to do this (which I have done before) you have to drain the fluids, undo the coolant hoses, fuel lines, power steering lines, take off the AC compressor, etc, etc, etc. Now I am looking 10-12+ hours. And I am supposed to be leaving tomorrow at noon to go see my college age daughter's crew team race in Ohio. I can just see the look on my wife's face when she comes home and sees the engine half out of the car. Not today I am afraid. So everything went back on until at least next week.

And now I have to ask myself if I have the engine out this far, another 2-3 hours and I can have the engine all the way out, split the trans and do the IMS bearing upgrade. But if I do that there is another $700, and should I do the new tensioners. What fun!!

Guess I will make these decisions next week.

[tholyoak]

Camshaft position 1 deviation -12.15

Camshaft position 2 deviation -02.45

These are adaptation values. The range for these values should be +/- 6 degrees. The thing to keep in mind this is 6 degrees at the crank, so 3 degrees at the cam. So your bank 1 cam is out by ~6 degrees.

Actual angle for camshaft bank 1 .1 (at idle) 25.94 (at 2,000 RPM)

Actual angle for camshaft bank 2 .3 (at idle) 24.74 (at 2,000 RPM)

This is what the motor thinks the actual cam angle is based upon the tab on the cam passing the Hall sensor on the head and the adaptation values.

These actual angles should be ~0 with variocam off and ~25 with variocam on. From these values you know that the variocam actuators are fine (as long as you get close to 0 with them off). You have an issue with the relationship of the tab on the cam with the hall sender. Either the cams are missed timed slightly or the tab on the cam is bent/damaged.

-Todd

Edited April 29, 2010 by tholyoak

[rb101]

Doug,

If you are going to pull the cam cover and check the allocation, you might as well also replace the cam tab since it had gotten bent at one time (rotor trim 996-105-129-52).

Rick

99 996C4

87 944S

[Dharn55]

Rick - I actually have an extra set of cams with the rotor trim. But they are a press fit, hard to get off, and also probably hard to get a new one on. I really think that I might be one "roller" fo the chain off, would not be hard to do and would account for the 12 degrees. So when I take off the cam cover I will see. Probably will have to actually take off the cams as the advance mechanism makes it hard to see exactly how the links line up. In any case we will see how it goes. I don't think the slight distortion of the rotor trim tab, if I did not get it quite straight, would provide for a 12 degree deviation.

Thanks for your thoughts.

[snorth54]

Thanks for the link. You are correct I have the Variocam Plus. I have found sveral good articles covering the Variocam arrangement.

I just replaced the IMS bearing at 20000 miles just for peace of mind. One suggestion I did not see on the posts is to cool the bearing with the installer assembled in your home freezer and use a ceramic or space heater to warm the shaft. I slid the bearing and driver into the shaft, wiggled it a little so it went in a little and was square and a light tap was all that was required to intall the bearing. I had preset the calipers so I would know the bearing was all the way in before removing the aluminum driver.

Sorry to drift off the camshaft topic, should be a different post.

[tholyoak]

For some reason you are still insisting your cam timing is out by 12 degrees. As I posted above, measured at the camshaft the rotational angle of the cam is out by 6 degrees from ideal and 3 degrees from spec. If the radius of your cam ring is ~2", that means it scribes out a distance of ~12.5" in one 360 degree rotation. If you are out 6 degrees from ideal, that is 1/60 of 12.5" or 0.2", if we consider you are really only 3 degrees out of spec, that is only 0.1". I highly doubt you can eyeball this.

If your cam timing ring was indeed bent (an important point you failed to mention) and that is the difference between how you timed bank 1 and 2, acoms razor would suggest this is your problem as you probably weren't able to perfectly realign the tab.

[Dharn55]

tholyoak - Thanks for all your input. So you are saying that the 12.5 degrees is at the crank, not the cam itself. I thought it was at the cam itself. I know that the advance of the cam by the vario cam mechanism is measured at the cam itself, not at the crank. Why do you measure the deviation at the crank, not the cam?

[tholyoak]

All the specs porsche gives for cam timing are relative to the crank not the actual rotation of the cam itself. The actual advance of the cam in an early motor is only 12.5 degrees of cam timing. It is 25 degrees of advance relative to the crank. Below are some excerpts from the service manual supporting my claim.

-Todd

[txhokie4life]

All the specs porsche gives for cam timing are relative to the crank not the actual rotation of the cam itself. The actual advance of the cam in an early motor is only 12.5 degrees of cam timing. It is 25 degrees of advance relative to the crank. Below are some excerpts from the service manual supporting my claim.

-Todd

Seems like it makes sense to me. With the Crank -- it knows where TDC is. And so relative to that tells you where the pistons are, etc.

If the main chain were off and you were measuring at the cam (i.e. locally) -- you might be fine there, but off globally.

mike

[sehorntx]

All the specs porsche gives for cam timing are relative to the crank not the actual rotation of the cam itself. The actual advance of the cam in an early motor is only 12.5 degrees of cam timing. It is 25 degrees of advance relative to the crank. Below are some excerpts from the service manual supporting my claim.

-Todd

Seems like it makes sense to me. With the Crank -- it knows where TDC is. And so relative to that tells you where the pistons are, etc.

If the main chain were off and you were measuring at the cam (i.e. locally) -- you might be fine there, but off globally.

mike

Dharn55,

What are the "roller" youre referring to? I had both heads off my engine for intermix, and somehow got timing correct by using your instructions. The chain is specifically marked to match the notches on the cams, where were the rollers?

[txhokie4life]

Hopefully this picture will help explain things.

There need to be 8 links inclusive (If I remember correctly) between this dot and the one on the exhaust.

If you are off a roller -- .i.e. the number of links between the two dots will not be exactly 8.

In other words, your timing will be off.

mike

[coleta]

tholyoak, you mentioned the deviation spec. is +/- 6 degrees. Where did up get this spec from? I found an old Porsche workbook that shows it at +/- 25, believe it or not. I'm gonna try and scan it so I can post it.

[tholyoak]

25 degrees is the amount of cam advance available in the early variocam system. +/-6 degrees is the allowed deviation from ideal. This value is right from the factory service manual

[coleta]

The reference explains the 25 degree advance but also says this:

So the 25 degree reference here is for deviation. Can you post your info or give the section were it's found?

Thanks Tholyoak

[tholyoak]

You are confusing two issues. If you monitor cam deviation while running the car, when the variocam kicks in, it will show up to 25 degrees from baseline. This is the variocam adavance, if you don't get this advance you have a problem with the variocam actuation. This is what your section is referring to. The maximal amount of cam advance available from baseliine. This is different than the amount of deviation that is acceptable without variocam actuation used for diagnosis of a static cam timing problem which is +/- 6 degrees at idle at operating temp with accessories turned off. The DME setpoints can be found in the factory diagnostic manual page 24-D8 to 24-D9.

[coleta]

I think I see what my confusion is. Your saying that when the cam advances both actual values, that of camshaft deviation AND actual angle for camshaft, will show 25 degrees?

And thanks for the reference.

[tholyoak]

The cam deviation is an adaptation value representing the deviation in the base timing from ideal. The actual cam angle can be used to determine if the variocam system is working or not. Actual cam angle will be ~0 or ~25 degrees depending on whether the variocam is activated or not. The adapted cam deviation should be +/- 6 degrees if the cams were installed properly.

-Todd

[coleta]

Hi Todd, sorry about this but I can't find your reference. I looked under On-board Diagnistics 5.2.2. The pages are identified by letters and then the page number for that letter section. After these letter sections the pages are then identified by the actual fault code.

My section D ends with page 8:

And has nothing to do with vario cam.

What am I doing wrong?

Thanks

Edited February 7, 2011 by coleta

[coleta]

Dharn55, did you ever fix this?

Camshaft position 1 deviation -12.15

Camshaft position 2 deviation -02.45

What did you find?

[Dharn55]

No I have never gone back in to fix this as it really involves dropping the engine. I did get the updated Durametric with the latest software and will check it again one of these days.

If I drop the engine to check the timing I am going to do the LN IMS upgrade too.

I also bought a tool set with the cam timing tool and should try to check the timing with this before dropping the engine. With the tool I should be able to see if the cams are off by one tooth on the chain. Just have not had the time to do it.

I do have almost 20,000 miles on the engine since the intermix/cracked head fix and the car is running strong. It seems it would not run so well if the cam timing is really that far off, may just be the tab.