Question about reman engines and IMS

[kcpaz]

Jake, what year did they start with the 9A1?

[Jake Raby]

Late in 2008..

I expect to begin seeing problems with those too.. Their is a reason why every flat 6 since 1964 used an "Intermediate shaft"... Removing that component was a mistake if you ask me.. Earlier engines used a plain "layshaft" bearing that didn't fail, but the shaft was still there.. Just like in a 964 based GT3 or Turbo engine.

We will be tearing apart our first engine of the new design in a couple of months. We are proudly voiding its warranty at 4K miles to get started on development and a big bore arrangement.

[kcpaz]

Maybe I'm ignorant (which is very possible since I've never personally rebuilt a Porsche engine) but why do you feel that an intermediate shaft is so necessary? At the risk of comparing apples and oranges, Subaru doesn't use an intermediate shaft (on their 4 cylinders, or their 6 cylinders) and IMO, they are better off for it. Why add another system to fail?. Reminds me of the Mitsubishi 4G63 motors with their balance shafts. "Enthusiasts" remove the shafts all together because they aren't necessary and its just one more system that can cause timing belt issues.

[JFP in PA]

Originally Posted by kcpaz

Maybe I'm ignorant (which is very possible since I've never personally rebuilt a Porsche engine) but why do you feel that an intermediate shaft is so necessary? At the risk of comparing apples and oranges, Subaru doesn't use an intermediate shaft (on their 4 cylinders, or their 6 cylinders) and IMO, they are better off for it. Why add another system to fail?. Reminds me of the Mitsubishi 4G63 motors with their balance shafts. "Enthusiasts" remove the shafts all together because they aren't necessary and its just one more system that can cause timing belt issues.

Not quite the same thing.

What you are referring to is removal of the balance shaft, not an intermediate shaft. The makes you point out use a rotating mass to dampen vibrations. The IMS in a M96 Porsche is not there for this purpose, the crank turns one end of the IMS, the other end turns the camshafts; remove it and the engine will not operate..................

[kcpaz]

Originally Posted by JFP in PA

Not quite the same thing.

What you are referring to is removal of the balance shaft, not an intermediate shaft. The makes you point out use a rotating mass to dampen vibrations. The IMS in a M96 Porsche is not there for this purpose, the crank turns one end of the IMS, the other end turns the camshafts; remove it and the engine will not operate..................

I didn't say they were the same, I was using that as an example of eliminating an unnecessary system that over complicates an engine. I understand that the M96 does not use a balance shaft. What I said was the Subaru engines which are also horizontally opposed and also come in 4 and 6 cylinder version do not use an intermediate shaft and have no reliability issues because of it.

And Subaru does not use balance shafts either.

[mikefocke]

because of course Porsche designed the 2009 and later Boxster/Cayman/911 engines without an Intermediate shaft. So it could be done. Why wasn't it way back when?

And if I recall the story, it was because the engineers were familiar with that design and the company was strapped for cash so they were reusing every bit of engineering in an attempt to get a new car out the door quick and cheap. And it isn't as if all IMSs fail (far from it) or that they all fail quickly so any fool could know the design was faulty. Consider that every 911 and Boxster would use this engine in '96/'97, it isn't as if the engineers wanted it to have problems...they were betting the company on the M96 engine.

We are now looking at the problem with the benefit of 20-20 hindsight and about 16-18 years of experience (from initial design of the engine till now). It seems obvious to us, but I'll bet few at the time were seeing the potential for problems especially faced with the economic realities of the time.

Every design is a compromise between the available time, budget, schedule, the technology of the time, the knowledge of the designer, the limits placed on the testing, the wishes of the thought-to-be potential customer, manufacturing costs, expected maintenance costs, internal company politics, etc. Get any one wrong and you lose the company if you were Porsche in the '90s.

As one who once had total product specification responsibility, it isn't that easy to get it right. Nor is it obvious it was right until perhaps years later. In my case 6 years after I wrote the specification and millions of investment dollars later...

Plus what you'd choose today in materials might well be very different than the materials available in the 1992 time frame which was probably about the time the M96 engine was being designed. New materials and new knowledge about how to use those materials are available now that weren't available to the designers back then.

[Jake Raby]

The cams are driven at 1/2 crankshaft speed.. That is accomplished via the IMS.

The surface speeds of lots of timing chains are being elevated..

Flaws take a while to note, the new engine was also subject to Porsche Accounting, just like the M96.

[kcpaz]

Originally Posted by Jake Raby

The cams are driven at 1/2 crankshaft speed.. That is accomplished via the IMS.

The surface speeds of lots of timing chains are being elevated..

Flaws take a while to note, the new engine was also subject to Porsche Accounting, just like the M96.

This doesn't justify the need for an intermediate shaft at all. Obviously there are a LOT of other successful engines out there that don't use intermediate shafts to accomplish proper operation.


Also, can anyone tell me why there was a need to drive the cams from opposite ends of the engine? Again, it seems unnecessarily overcomplicated.

[jcb986]

The design for the IMS may have been fine if they had figured how keep the bearing lubricated without drying out and sizing. Maybe something like a American V8 main bearing....you keep oil moving through it to keep it lubricated.

[kcpaz]

Originally Posted by mikefocke

because of course Porsche designed the 2009 and later Boxster/Cayman/911 engines without an Intermediate shaft. So it could be done. Why wasn't it way back when?

And if I recall the story, it was because the engineers were familiar with that design and the company was strapped for cash so they were reusing every bit of engineering in an attempt to get a new car out the door quick and cheap. And it isn't as if all IMSs fail (far from it) or that they all fail quickly so any fool could know the design was faulty. Consider that every 911 and Boxster would use this engine in '96/'97, it isn't as if the engineers wanted it to have problems...they were betting the company on the M96 engine.

We are now looking at the problem with the benefit of 20-20 hindsight and about 16-18 years of experience (from initial design of the engine till now). It seems obvious to us, but I'll bet few at the time were seeing the potential for problems especially faced with the economic realities of the time.

Every design is a compromise between the available time, budget, schedule, the technology of the time, the knowledge of the designer, the limits placed on the testing, the wishes of the thought-to-be potential customer, manufacturing costs, expected maintenance costs, internal company politics, etc. Get any one wrong and you lose the company if you were Porsche in the '90s.

As one who once had total product specification responsibility, it isn't that easy to get it right. Nor is it obvious it was right until perhaps years later. In my case 6 years after I wrote the specification and millions of investment dollars later...

Plus what you'd choose today in materials might well be very different than the materials available in the 1992 time frame which was probably about the time the M96 engine was being designed. New materials and new knowledge about how to use those materials are available now that weren't available to the designers back then.

I don't understand why there was even a reason to produce a different engine for the "lesser Porsches" I mean, it's not like they needed two flat 6 engines in their line-up. Why not continue the tradition of using the same basic engine in all of their cars with tweaks here and there to fit the specific need. Every other manufacture does it. They have a few engines that share the same architecture, and they modify them to suit the specific application. GM did it on a HUGE scale with the LS engine. I mean the same basic engine found in a common work truck, shares much of it's design with the LS7. They even made a FWD version. If Porsche was going to produce the "GT1" engine for the Turbos, GT3's etc... why not just use the same engine for everything? Even if they are a little more expensive to produce (which I doubt) how much did it cost to start from scratch and produce the M96?


It just seems to me like they held onto the M96 for about 5 years too long. I mean, in it's entire production, was it EVER a big hit? I would say the opposite. I do not consider myself a "Porsche Guy" (although I know a little about the brand)so my perspective comes from other import manufacturers, and even in circles of people who don't know the difference between a 986, 968, 996, or 997, the Boxsters (first to receive the engines) have a bad reputation for engines that self-destruct in significant ways. If I were Porsche, I would be embarrassed by the M96 and would have done something about it ASAP, not drug it out for 14 years. That's just my $0.02 though.