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IMSB problem or not?


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Firstly I want to say that I’m not a Porsche expert. I’ve owned my 2001 Boxster for 3yrs now, and it’s been an absolute pleasure. And whilst I am not a Porsche expert, I am a retired aircraft maintenance engineer who still loves all things mechanical, especially fast cars!

Having previously owned mainly Australian Muscle Cars, I was hesitant about buying the Porsche, especially after reading ‘forums’ that shone a light squarely on the ‘IMSB’ problem that seemed to be the archillies heal of the brand. I researched the Boxster for months and spoke to as many people as I could about the Boxster and it’s perceived problems, and I decided that based on the information that I’d gleaned from Porsche techs, mechanics and owners, I’d take a serious look at the Boxster.

I ended up buying my 2001 2.7 Tiptronic, which had 140,000kms on it, but was owned by an 80yr old gentleman who serviced it to death, and the guys age didn’t hold him back, he scared the shit out of me when he took me for a test drive, so the car wasn’t idled around the place which I was told is one of the things that kill a Porsche.


So 3yrs down the track and I get a Porsche Mechanic to carry out a major service on the Boxster (prior to this I carried out oil and filter changes every 5,000km or every 6mths). When the mechanic dropped the oil and removed the filter, he found a lot of ‘material’ in the filter (this had not occurred on any other oil / filter change). First thought was the ‘dreaded IMSB’, and there was talk of getting another engine to drop into the Boxster. Needless to say the service stopped right there and then, the mechanic put the filter back on and poured the old oil back into the engine. So now I had to make a decision regarding the future of my Boxster, rebuild or replace?


After the mechanic left I sat down and thought about it, then I decided to pull the filter and drain the oil and drop the sump to get a better idea of what was going on in my engine. After draining the oil and removing the filter, I cut the filter open and washed all of the material in the filter into a clean container. What I discovered was that the material in the filter was not ferrous metal or alloy, in fact the material was like a hard rubber? And once the material was cleaned it was ‘dark green’ in colour? I rang the mechanic who said he had no idea where the material could come from, but after hours of searching I found a post on a forum about someone who had exactly the same material in their filter, and after exhaustive investigations they found that the dark green material came from the ‘variocam tensioners’, yep that’s right they had pulled their engine down to locate the source, and in the process discovered that the Variocam Tensioners weren’t operating correctly, they even cut the tensioners in half to show the green seals that had deteriorated and flowed into the oil system, yahoo! I’ve found my problem.

This explained a lot of things for me, you see my car had the dreaded rattle on start up that I was told ‘was completely normal’, really? I know that the 5 chain engines have a reputation of rattling during a cold startup, but I still didn’t believe this was ‘normal’. So with the information regarding the Variocam Tensioners, I set about removing the transmission and engine. Now while I had the engine out I decided that I’d change the IMSB to be safe, the thing is that when I got the Bearing out it looked and felt ‘Brand New’, no deterioration and smooth as silk (it was a factory ‘dual row’ bearing), that was the good news.

Now that I had the ‘Cam Chain’ tensioners out I tested them, and 2 of the 3 were defective (I wonder if that might be the source of the dreaded rattle!). But after the Variocam Tensioners were removed I cut them in half and found that the ‘green ‘o’ ring seals’ were intact, but. In the Variocam Tensioners there is a large ‘phenolic’ seal, and this seal had worn the bore of the Tensioners to the point were they were allowing oil to bypass the seals, hence the tensioners weren’t doing their job. Add to this the fact that the wear pads on the tensioners were badly worn as well (the Cam Chain Tensioners wear pads were in great condition and the mechanic said that that was because the tensioners weren’t pushing the pads onto the chain hard enough to wear them).


So, after replacing the IMSB, the Variocam Tensioners and the Cam Chain Tensioners, the engine and transmission were fitted back into the car. On the initial start up (after removing the fuel pump relay and turning the engine over a few times), the engine started with not even the slightest sign of a rattle! And after driving the car since the overhaul it has not rattled once even after leaving sit for a week without starting it! So when someone tells you a rattle on start up is ‘normal’, I can tell you from experience that it’s not!


What did I learn from this experience, well I learnt that there are what I believe are more pressing problems that need attention in a Boxster engine than the IMSB, and I’m not saying that the IMSB isn’t a problem (but it seems that engines fitted with the ‘dual row’ factory bearing aren’t as susceptible as those with the ‘single row’ bearing), and a catastrophic IMSB failure is a death sentence for an engine. But if the Tensioners in your engine fail, then the end result will be the same if not worse than the IMSB failing.

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6 hours ago, 9er said:

Good write up, thanks for taking the time.

Although the bit about the mechanic replacing the filter and pouring the old oil back in is going to have me waking up at night, for a while.

We did this because I was not going to drive the car or even start it, better to have something in the engine rather than nothing, and only hand tightened the filter to plug the hole basically. As it turned out I drained the oil and removed the filter the next day after I decided to investigate further.



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5 hours ago, Zelrik911 said:

Would the wear on the  Variocam Tensioner seals have affected the valve timing between the 2 banks?

I recall that a difference in timing between the banks has been used as a sign that the IMS is wearing out.


I doubt it, the failure of the ‘Cam Chain Tensioners’ would have been a more likely culprit if there was a difference between the two banks, but unfortunately I had the engine basically ready to drop out when the mechanic came back, and to be honest I’d already purchased all of the Tensioners and the mechanic had brought new guide paddles with him (which as I explained we didn’t need because the originals had virtually no wear) so I wasn’t really worried about the current valve timing accuracy.

i think there’s a greater danger to valve timing due to inoperative / faulty Tensioners and worn pads, also if you think about it if the tensioners aren’t doing there job and the cam chains are basically flapping about, then surely that isn’t good for the IMSB?

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