elgy

I posted this on 986forum.com, but have not as yet had any responses,
http://986forum.com/forums/performan...6-engines.html

In Help Me DIY's (TTGator) recent forensic video on his failed 2003 2.7 Boxster engine he reveals that Jake Raby diagnosed the problem as a mushroomed valve lifter. According to Jake this is a common problem caused by an improperly machined camshaft. On cylinder one an intake valve lifter had broken and and the second one was about to fail.
The video is here, explanation is after 7:00 minutes:

I searched for information on this failure but found nothing... does anyone have more information? Specifically, what engines are affected? My assumption is that the problem would only be with the 3 chain engines. If 5 chain engines are affected I will have to pull the valve cover and inspect the lifters on the 3.2 that I am preparing for installation in my car.

dougn

lets see a close up of those cam lobes!

Porschetech3

I saw one of those a decade and a half ago, but just one , so it wasn't common back then but maybe it is now....

The engine made no noise, ran smoothly, but would set a misfire code if you reved past 5k rpm...only one intake valve was opening...

Seems like it was a 2.7 and under CPO Warranty...I remember doing the job in situ, didn't removed the engine, did it in the car...

elgy

Was it a 5 chain or a 3 chain engine?

dougn

But whats going on with the cam? How could a cam be so far out of whack?

Porschetech3

I don't remember , I know for sure it was a single stage lifter and not the dual stage "Plus" lifters..

dougn

The whole cam looks weird. Looks rough

BRS-LN

Very common with this particular engine designation, especially the bank 1 intake cam, specifically #1 cylinder inboard lobe.
Jake showed me this while profiling one of these cams last summer for his book. He was able to measure the differences infinitely. I may be able to find a phot of the plot.

dougn

Besides being ground wrong, none of the lobes on the cam in the video has a shiny ground finish. I guess I would like to know how an incorrectly ground cam caused the lifter to become damaged

TTGator

That’s my video BTW
According to my understanding of what Jake was telling me is that the mis-machined cam lobes don’t rotate the lifter fast enough.

BRS-LN

Camshaft lobes have critical dimensions that can't be seen and are even hard to measure in some cases. If the lobe has an improper taper, or has runout it will make a vast impact on the surface speed that the lifter rotates at in operation. Much like the camshaft lobe, the lifter has a crown radius that works in conjunction with the lobe characteristics to create this surface speed. If things don't match up between the two, the lifter stalls, wear goes up and the lifter fails after some time. The lifter fails more frequently because it is a touch lighter on the Rockwell hardness scale compared the to cam lobe.

TTGator

Slightly more detailed answer ☝️😂

dougn

I did not know the lifters rotate!

elgy

This is very interesting... but still no answer on what engines are affected.

BRS-LN

If they don't rotate, they don't live. The only lifters that do not rotate are nested tappets in the vario- cam Plus engines, which have a 1.25" radius on their crown to match the lager camshaft lobe on those engines. These cannot rotate due to having a second portion of the lifter which extends to meet the smaller lobe of the camshaft at idle and low speed.
Almost every engine produced over time has lifters that rotate under load, even a Briggs and Stratton. Roller lifters typically do not have bodies that rotate, because they have a roller wheel that traces the circumference of the camshaft lobe. Porsche designed this set up for the Harley V rod engines as a little known fact.

I confirmed with Jake, and the engine that suffers from this issue is the M96.23 which is a 3 chain 2.7 engine used only in the base model Boxster. He says that he has seen something similar with the M96.24 3.2 variant of the engine, but not very frequently. These are unique engines since they are 3 chain design, but do not utilize variocam Plus.
I asked him for some plots from his Cam Dr. studies, and if he provides them I'll post.