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Old 05-17-2012, 01:53 PM   #1
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Intermediate Shaft Question

Is Porsche the only manufacturer that uses an IMS in their cars? And if so, why? I haven't heard of any other car manufacturer having these problems. I am assuming that Porsche knows how to build engines. Than why are we constantly reading about IMS failures? And if Porsche knows about this problem and has not fixed it, than why are we a bunch of lemmings and continue to buy these cars; probably too rich and don't know what to do with our money, or just gluttons for punishment. Either way, this is the first car I have ever owned that scares me to death every time I get in it. Never knowing when it will blow up. But, then again, I enjoy driving it and it looks pretty cool. Maybe that answers my question on why we keep buying this defective product.

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Old 05-17-2012, 03:15 PM   #2
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Automotive design & packaging is filled with compromises. The Porsche 986 Boxster is the most enjoyable vehicle/ object I have ever owned. Currently 986's are available at Bargin prices due to the IMSB issue & there is a semi permanant solution to the issue for $1,500, so what's not to love?
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Old 05-17-2012, 03:38 PM   #3
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Soetekouw......

Most twin cam engines have an intermediate sprocket (chain drive) or roller (belt drive) to lower the camshaft rotational speed to the required half engine crankshaft speed.

The main reason the M96/97 engines have a hollow "shaft" running the length of the engine is because of Porsches (financial ?) decision to have both cylinder heads identical, requiring a drive from the front for one cylinder head and a drive from the rear for the second cylinder head. If Porsche had designed, built and accepted the extra cost of a second "mirror image" cylinder head then most of the IMS drama would possibly not have eventuated.

The other alternative is to reduce the camshaft speed down the 50% by altering the size of the camshaft sprocket, which the new DFI engines use I believe. But therein lies another potential wear problem in that the timing chains are now running at engine speed - up to 7,800 rpm on the new Boxster engines - so its a matter of time as to how the chains, sprockets and tensioners on the newer engines lasts.
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Last edited by Steve Tinker; 05-17-2012 at 03:42 PM.
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Old 05-17-2012, 07:44 PM   #4
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The IMS isn't an issue.. The IMS bearing is the issue.

In case you didn't know, the IMS was previously called the "lay shaft" in the aircooled engines and EVERY 911 engine from 1965 used one. Those didn't have any issues due to the method used for their bearing surfaces.. Also the famed Fuhrmann 4 Cam Carrera engine used an "IMS" as a layshaft as early as 1955 without issue.

There is nothing wrong with using an IMS, there is something wrong with using a sealed bearing to support it.

Here is a typ 547 4 cam Carrera engine with layshaft, no sealed roller bearings here~
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Old 05-18-2012, 04:08 AM   #5
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I doubt any bearing manufacturer eg SKF, FAG, NSK etc would have endorsed Porsche's use of a sealed bearing in this application.
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Old 05-18-2012, 06:02 AM   #6
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Thanks for the responses.

So the problem is the sealed bearing and it will cost approx. $1500 to replace it with a better bearing, later. Could Porsche have done that for only a few dollars extra when they build the engine? If they don't want to do this as part of their quality build, maybe they should have this fix as an Option. I much prefer spending an extra $50 for an engine fix than I would selecting a leather covered ash tray liner, when I option out the car on purchase.
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Old 05-18-2012, 11:43 AM   #7
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Quote:
Originally Posted by Soetekouw View Post
Thanks for the responses.

So the problem is the sealed bearing and it will cost approx. $1500 to replace it with a better bearing, later. Could Porsche have done that for only a few dollars extra when they build the engine? If they don't want to do this as part of their quality build, maybe they should have this fix as an Option. I much prefer spending an extra $50 for an engine fix than I would selecting a leather covered ash tray liner, when I option out the car on purchase.
The problem has been solved for 4 model years now. If you want a Porsche without an IMS just buy a 2009 or newer model. I can promise you they don't care about your 10-year-old used car. You'll need to go to the aftermarket for solutions there.

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