MY2000 at 60k miles (new IMSB 5k miles ago) Durametric showed a bank 1 reading of -7* with bank 2 at -1*. The engine runs perfect with no codes and no debris in the sump or filter but with that high of a reading I figured I'd tackle bank 1 sooner rather than later. I'd read several posts by Rennlisters who have done the job (De Jeeper, Mike Murphy and, of course, Porschetech3) and watched several Youtube vids (Man in a Garage, NewArt, Help Me DIY and FunAhead TV) so I had a fairly good idea and a visual of what needed to be done. The job was not hard at all taking maybe 10 or 12 hours on the quickjack and using the ebay tool kit. Here's a few pics and notes that might be of help to some:
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• Removed the necessary stuff: bumper, AIS, muffler, swaybar and heat shield but I also removed the engine mounts so I can drop the engine enough and pivot it sideways a little. This is to clear (barely) the installation of the scavenge pump while the valve cover is installed.
• Remove the O2 sensor so the sword alignment tool will fit (see pic). It was also necessary to remove the intake alignment bolt from the sword tool.
• The manual says to substitute fixed tools for all three tensioners but they seem to not be available and no one uses them.
• I installed a new scavenge pump that is designed different than the original - the rotor case is bolted on the inside, not accessible from the outside. More on this below.

So I installed the new guides and sealed the cover just as others have done with no issues but I like to run the engine up to temp when possible before putting it all back together. This way I can check for leaks or other problems and also get a new Durametric reading. With the old scavenge pump you can take the cover off and remove the internals then just put the cover back on to run the engine and then easily remove the cover to adjust the sprocket settings as needed. I was disapointed that after this work the Durametric reading dropped to just -4.9* from -7* but this is what other's were seeing too. Not happy I removed the scavenge cover and nudged the sproket forward a couple mm (I recall Porschetech3 mentioning this in a post) and the next reading was +1*. I did this one more time (nudging it back) getting a reading of -1.7* which i was happy with (getting a delta of 5* just by moving the sprocket a couple mm implies that not just pad wear is a factor but chain stretch is and not using the tensioner tool will also affect the Durametric reading). With this reading I installed the new pump by pry-barring the engine to the side a couple cm to fit. Hope this makes sense.

Here's a few pics. Hope this helps others (sorry, don't have the skill or looks to do a Youtube vid). I'll likely tackle bank 2 next year.

I thought they'd be worse



New pads installed, lubed & ready for the cam holder tool.

O2 sensor removed and it fits but barely. Take the intake bolt off the sword and use a mirror to align. I used this tool 3 times to dial in the right setting.

Old pump on top has the assembly bolts on the outside. Installing the new pump requires pivoting the engine sideways a couple cm.

Final setting. Note that just one mm either way makes a big difference.

Final result, after 30 mile drive.

 

Nice work. I really wanted to "adjust" the cam gear onine to dial in the values but the motor blew before u could get to it. Glad it worked out.

 

Nice thread and good work. Good note on chain stretch. Those pads don’t look too bad, but it’s still good you changed them out.

 

Thanks both. With the old scavenger design I could probably go in there and adjust the cam gear in an hour or two. The new design scavenger must come out as a whole unit, more work. (I really don't want my engine to blow up as a Mezger is not in the budget)

I will also note that, besides any chain stretch, I think just pumping oil into the chain tensioner(s) is not enough and probably a bigger cause for not getting a low deviation result. They loose oil as soon as they are installed causing the chain to be slacker than the normal operating position. I was able to use a plastic lever under the long ramp and move it easily. Adjusting the sprocket compensates for this (and not using the overly expensive, unobtainium fixed tools). The sprocket should not be adjusted to compensate for the worn chain pads only. This would be bad, just masking the problem.

 

Yeah, tensioner replacement is also not a bad idea on these engines, as I’m sure many start to leak by this age. It can also really help noise on startup.

 

You must remember that the "cam deviations" is read at the intake cam, yet the "adjustment" is made at the exhaust cam..Quite a few things are in-between the two places, most important and problematic is the chain..

The chains do not actually stretch, they wear at the pins and plates in an oblong fashion that makes them seem to be stretched, but they are worn that way and makes the chain longer..

There are chain tool gauges that can measure the wear and a 3% increase in length is the "throw away zone", but on the M96 I use 1% as the rule..

 

If you care to share: What is a typical mileage you have seen for 1% and for 3% wear?

 

Nudging... means you remove the scavenge pump, loosen the 4 bolts holding the sprocket to the exhaust cam, and pry the sprocket in the cw or ccw direction ? is that it?

 

U lock the side that has good numbers and the crank puley. Then u remove the scavange pump, lossen the 4 bolts and "cheat" the gear. U can spin the cam with the timing adjustment tool. I dont remember what directiion but it think it might be side dependant? Its a tight fit while motor is in the car and the only way to check it is to reassemble so its a process.

I was gonna do this in motor because i had new pads and new small chains so there should have been zero "stretch" between the 2 cams. My issue was most likely with the long chain that cant be changed without splitting the motor.

 

Cheat the gear ... you mean "turning the exhaust cam shaft in one direction by 1mm" then reassemble it and run it to see if it improves or not. If not, you repeat the process but turn the cam shaft the other direction?

 

Well turning the cam shaft or rotating the gear does the same thing. It creates an offset in the timing to adjust for the "stretch". I think it would be easier to rotate the cam instead of pulling the cam gear with the chain and tensikner pulling on it.

At some point Skip told me witch direction to spin but i cant find the thread. Im sure u could also do some math and determine approx how far each mm would move the deviation but i think it should just be done with small movents of trial and error. As i said its a process.

 

Looking at the back of the engine, the crank pulley turns clockwise, so all rotating parts turn clockwise: crank, IMS, camshafts. Advancing the exhaust cam further clockwise also advances the intake cam (which has the sensor) reducing the deviation.

The cumlative total of the deviation is crank sensor to intake sensor:

• Just pinning the crank. If you pinned the crank with a 1/4 drill bit for example, it would be sloppy and affect adjustments, so propperly pin the crank.
• All the chain sprockets wear but not much, so minimal deviation.
• All the chains: IMS short chain. Cam long chain. Cam to cam chain. Measured from crank sensor to exhaust sensor, this can add up.
• The chain tensioners.
• VarioCam pad wear.
• Of course if the IMSB is going bad, but that's a separate story.

Once the VarioCam pads are replaced I think the tensioners and chain wear are cause for coming up short from a desired result and this wear only shows as a deviation while the engine is running. Advancing the sprocket compensates. There's a reason Porsche made a fixed tensioner tool set for this job but it's expensive and I don't think it's even available any longer. I'd even thought of welding my old tensioners to make them a "fixed tool".

 

There are too many variables to make a prediction of chain wear..I have seen engines with 50k miles that were above 3% and engines that were 125K that were still under 1%..Miles is not a good measurement of wear..

The main contributors to wear is oil quality and freshness, average RPM, hours of operation...the things that are never fully documented or can be accurately estimated...

To complicate making chain wear estimates even more, all things have a "natural harmonic resonance" and the constant loading and unloading of the valve springs also cause a harmonic vibration of the valve train and chain. There is always a point where these cross paths and makes it worse and if you are unfortunate enough to spend a lot of time at the cross point the wear worsens...The M96 engine seems to be most happy in the 3500-6500 RPM range...

To "nudge" the cam deviations you want to remove the exhaust cam plug and rotate engine until the slot lines up and the fixing tool fits and "locks" the exhaust cam.

Then remove the scavenge pump and loosen the 4 exhaust cam bolts..

Measure the circumference of the crank pulley in decimal inches or MM and divide by 360, this gives you degrees in decimal inches or MM .

Mark outer diameter of crank pulley to a reference mark on the case,

then make a mark the number of degrees you want to change in either clockwise or counterclockwise direction..( moving the crank pulley counterclockwise will advance the exhaust cam timing, moving the crank pulley clockwise will retard the exhaust cam timing)..

turn the crank the desired number of degrees then torque the 4 exhaust cam bolts...

Re-install the scavenge pump and remove exhaust cam lock and install new cam plug...done....

 

I think I read somewhere the max cam resonance is around 2,200RPM, which is 30mph in 3rd gear in my car. This speed is the most common speed in the U.S. on regular town/city roads, and most people probably use 3rd gear too. I use 2nd at 3,000 RPM wherever possible.

 

I don't have the tools, skill, or patience for this but I envy those who do. I wrote a check...a fairly big check to have the chains, pads, and tensioners replaced when my cam deviations were out of whack.