Greg Lab

This is from my P car guy in the biz:

"There is a small metal plug that's inside the hollow intake cam that somehow moves further into the cam and blocks the oil passages for the lifters. When the passage is blocked the oil will not flow and pump up the VarioCam Plus portion of the lifters and you end up not getting the higher lift profile of the cam. This makes that side of the engine not produce power in the upper RPM range when the valve are to be at high lift. This feature is only on the turbo Mezger engines and not the ones in the GT3. "

It's a big dealer, only seen a few, felt it was pretty rare.

speed21

This is the effect. The cause I can imagine is to do with as M42racer has articulated - a variance in manufacturing tolerances combined with the harmonic vibrations. It makes sense to me anyway. Operationally all engines will vary (climate, terrain, driver habits etc), so where the tolerance of the interference fit is on the looser side of the allowable equation the risk becomes greater for this problem to occur. Tolerances can be extremely critical. I recall the cold start flareup issue in this engine as another example where tolerance was too far one side yet allowable at the time by the manufacturer. Correcting the tolerance in this instance becomes a far more costly exercise...and pinning, whilst evidently considered a band-aid fix which the manufacturer is not prepared to currently entertain becomes the sure fire method in the long run. Furthermore, the racing mezger is entirely different and as explained before the street engine wears the bare block only, the rest being quite different, especially when looking and evaluating the reliability between the street and race variant.

Kevin

Greg, it's not a plug but a metal sleeve. Since I have pinned a handful of these camshafts. It is a loose sleeve that rotates.. Engine crankshaft harmonics on this engine doesn't come into play with the relative low RPM redline. Porsche has done a decent job at balancing the crankshaft, rods and pistons. The flat 6 is inherently balanced. If balancing was an issue, the 130mm intake camshaft bolt would be shaken out of the camshaft. You'd also have the exhaust cam bolts back out. And since there are ZERO guide pins or lock nuts to secure the vario cam or exhaust cam gear>>they would loosen up. WE would see camshaft deviation errors in the statistical population. To date, I haven't seen or heard of any.

Like I wrote in a earlier post, it's a "lottery" type failure. When the sleeve rotates, your numbers up..

speed21

It still does not explain the most logical reason for why the sleeve has begun to rotate inside the cam, causing the oil blockage. I though m42racers report was a reasonable suggestion where tolerance and vibration has bought about the looseness and subsequent turning of the bush into the blocked position. I still come back to the fact that there is a reason for all failures and it is in establishing the precise cause. It simply cant be just called a lottery situation when there are obviously factors behind the problem occurring. If there wasn't, then why does the failure not occur upon immediate start up of the brand new engine?

Kevin

The camshaft supplier to Porsche had to invent a new process. New design> manufacturing process.
The intake camshaft is hollow, a bolt passes thru the Vario-cam module and threads into the hollow portion of the camshaft. Between the vario-cam module and the fastening bolt threads (or attachment point) is the sleeve with holes drilled in it. The constant cycling of the vario-cam solenoid will pulse the oil thru the sleeve as the camshaft advances. I believe that it's the pulse that is loosening up the sleeve that is PRESS FIT, in the hollow intake camshaft..

If we had a crankshaft vibration or harmonic caused by the crankshaft rotating assy in "this" engine we would have more components loosening up.

The camshaft sleeve bore has deviations between camshafts due to manufacturing tolerance errors. One of the cures to fix this is to pin the sleeve. This is a permanent fix. The sleeve will not be able to rotate in the gun drilled hollow bore after the fix.

Greg Lab

As I understand it, the turbo has vario cam plus (changes timing and lift), whereas GT3 has vario cam (just changes timing). Could that explain why the issue is just with the turbo and not GT3?

speed21

Makes sense as well. I do agree that a vibration strong enough to dislodge a press fit bush has the potential to cause issues in other areas. The pulsing of the oil sounds plausible as being a contributing factor along with an over deviation in tolerances between cams. Possibly there are other contributing factors as well associated to operating conditions and driver usage habits. Low rpm idling environments, a lack of natural engine ventilation creating an expansion in certain areas not optimum cooled by the water circulation within the heads can tighten up clearness in that area creating an environment for scuffing/seizure/rotation. Has there ever been signs of scuffing or seizure found on the bush or are they always found in a loose rotated state, and unmarked in that regard?
I don't suppose you have an assembly diagram, or photos showing the physical appearances and location of each components involved?

Also what was the new process the manufacturer had to invent to stop the problem? Was it just a tighter interference fit? Or was the oil recess /hole in the bush expanded/increased along the length of the bush? So if it turned the oil still had adequate passage?

Kevin

The new process is in reference to building this new camshaft design vs the 996TT camshaft (no bushing).

Cincyscott has posted pictures of his camshaft failures which shows the sleeve.

The repair process requires the relocation of the sleeve and pinning it to keep if in place.

speed21

Thanks Kevin. I checked it out on Cincy's thread and can see exactly what you mean re the physicality of bush and camshaft. Seems odd why the boffins saw the need to even have a bush really. I guess in hindsight they should have either made the cam journals larger in DIA, using no bush at all or, used a shrink/interference fit rather than a press fit. Maybe the idea of the sleeve was to provide a better wearing material than that of the camshaft journal? Anyway... it is clearly an inherent design issue there, fraught with problems where the fit of the bush becomes altered during operation causing blockage to the oil feed. I couldn't imagine them replicating that mistake into any future engine.

saabin

Lots of good discussion here, thanks all for the info!


Gotgolf,

So I finally got ahold of the guy you recommended.. And a big thanks to you! Same policy was over 400 cheaper, so I decided to upgrade and get the 3/36 policy..

L_perm

Does this issue always happen in the same place? Same camshaft, same sleeve?

If so, doesn't that mean it is very likely a manufacturing defect (like others here have said)--assuming there are other sleeves elsewhere.

Or, are there two (or four, or eight...) sleeves, and this can happen to any of them?

speed21

Looks to be only the one sleeve on each cam. The sleeve provides the #1 cam journal a larger diameter so to better accommodate for additional load placed on that journal from the attached components/gears/drive chains etc. The manufacturing or design defect is referred in the sense that the bush/sleeve can rotate due to inadequate interference fit. Also if the replacement cam and bush have the same PUSH fit then pinning is the only surefire way of dealing with it permanently.

bondjockey

This reminds me of the header and valve guide issues on my old F355. Fix it the right way (i.e. pin the sleeve) and forget it. I'm leaning toward self insurance sine the cost of the warranty vs the cost of the cam repair has about a 3 yr break even. Since I plan to put only 2-3k miles a year on my car, it is a chance worth taking.

Btw this ignore feature is really nice

Kevin

Louis, you have two intake cams that have the sleeve. I called it a lottery because you don't know which one will fail and when it will fail. It may never fail... This is a repair that I would just wait till you get the CEL.

m42racer

This is not what I understand and not what I was told. I was told that engine balance and harmonics are two very different in balance. One is based upon rotating and reciprocating masses and the other, the more dangerous type is based upon torque pulses.

I was told these engines suffer from a low speed harmonic and it is this vibration that loosens the actuator bolts, breaks Oil pump gears etc. Not theory, but fact. It happened to me. Most have no understanding of this and the common thought is these engines are naturally balanced. Not true. Many have broken crankshafts. A VW is a flat four engine that would have the same quality and those cranks break all the time from the same effect. An understanding of engine balance and the difference between the two is important.

As for the sleeves coming loose but not the bolt, the sleeves are not held in the cam by the tension of the bolt stretch, but by the interference fit into the camshaft. The motion of the actuator certainly could attribute to the sleeve coming loose. No question. But the high frequency vibrations induced into the Valve train would have a greater effect. The motion of the actuator is a lot slower and may have a lesser effect.