Hello Thom.
Since this subject is very interesting for me as well, I have done some research on it.
(although I don’t have rattle, my cam deviation is -5,-6)
I will try to answer some of your questions, and hope some others will chime in, to correct me, or add more info.
1. Are the variocam pads that ones that wear out as the miles pile up?
- Yes. The variocam pads are responsible for cam deviation.
2. If so, am I right that one must remove the engine from the car and split the case to replace them?
- No. in order to remove the cam pads, you will need to remove the camshafts.
To do that you will need to lock them both (using a special tool) and remove the cam covers. It can be done when the engine is still in the car.
(process is well documented in the 101 book)
3. Are there are other pads that the chains run on?
Yes. Look at this diagram.
Porsche Boxster Camshaft Parts
parts 33,30,19,22 (and the cam tentioner pads 9)
4. Are these the ones that wear out and lead to the chain jumping timing?
I think all worn pads can lead to jumping timing. However, most likely is the pads for the IMS to cam chain (30,33) and the IMS tentioner pad (19)
5. Does one need to pull the engine and split the case to replace these other pads?
Still looking for an answer on that. There is no need to split the case for sure, but Wayne (from pelican) wasn’t able to tell me (in another tread about this subject) if it can be done with the engine in the car.
Separate from the pad question, my search of the bulletin boards suggests there are three chain tensioners in the M96 engines.
1. Am I right about there being three?
Correct. 1 tentioner is for crank to IMS chain (part 35), and two tensioners for IMS to cam chains (24&34).
When doing IMSB retrofit you need to remove 35&24. They are located at the bottom of each bank, on the transmission side.
The third tenssioner is located at the top of bank 2, right under the AC compressor.
2. Are these a potential failure point that allows the chain to jump timing?
I believe in extreme cases when the pads are completely worn out, then yes.
I read on the forum some posts about brown plastic particles in the oil. I guess it’s one of the symptoms.
3. Does one need to pull the engine to replace the tensioners?
No. see answer to question 1.