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- - Question about reman engines and IMS (http://986forum.com/forums/showthread.php?t=27187)

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.

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.

Quote:

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.

Quote:

Originally Posted by Jake Raby

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.

Quote:

Originally Posted by kcpaz

Its impossible to make my point here on the forums.. And its nothing but hypothetical anyway.
Practical application and time will illustrate the weaknesses of the "IMS-less" engines, as with every engine throughout time.

What people generally don't understand is the "lay shaft" as an intermediate drive for the valve train has been in place since the mid 1950s with Porsche engines. This is depicted here in this image of a 1955 Porsche Spyder engine I was working with a few years ago.. That shaft below the crank is the lay shaft, it transmitted mechanical energy through bevel gears and shafts up to the exhaust camshafts, that then drove another shaft and bevel gears to drive the intake cam, just like an M96, the only difference is chains Vs. bevel gears.
http://www.rdtlabs.com/Pictures/4cam...pics%20307.jpg

Notice the plain bearings, not a roller bearing like the M96.
http://www.rdtlabs.com/Pictures/4cam...pics%20303.jpg

Shaft that is driven by bevel gears, driving exhaust camshafts
http://www.rdtlabs.com/Pictures/4cam...pics%20112.jpg

Exhaust cam and bevel gear to drive intake cam
http://www.rdtlabs.com/Pictures/4cam...pics%20115.jpg

http://www.rdtlabs.com/Pictures/4cam...pics%20272.jpg

The moral of the story is the fact that Porsche used an IMS style design since 1955 when this engine was produced, the IMS was NOT a new design for the M96, but the roller bearing support Vs. plain bearing support was. The IMS isn't the reason for engine failures.

We'll see just how wise removing the IMS was in time.. We are already beginning internal development on the "new" engines.

Quote:

Originally Posted by Jake Raby

The IMS isn't the reason for engine failures.

I understand that, and I know the bearing itself is the only reason most people even know that the M96 has an IMS. It just seems to me like if there was a way to eliminate the IMS all together, you would be better off, and in-fact, other manufacturers have been able to. Now if you are saying that there is a possibility that the current design of the 9A1 would have benefited from having an IMS, I can't argue because I can honestly say I have absolutely zero experience with that engine, but based on what Subaru (just an example) has done with their engines, I don't see why Porsche wouldn't have the ability to make it work too.

Quote:

Originally Posted by kcpaz

Some component must reduce camshaft speeds by 50%, no matter what the engine may be.. In my experience you want that 50% reduction to occur as early in the mechanical "chain" as possible to reduce surface speeds of chains and etc.

When I first saw the proposed "new engine" I knew it was going to be hell on timing chains.. From the reports that I hear within some dealer networks I am part of failed timing chains are occurring.

Quote:

Originally Posted by kcpaz

The reason why the cams are driven from the opposite end of the engine via the intermediate shaft is because Porsche can use the same cylinder head on opposite banks of the engine. If they used the same end to drive the cams, then a "mirror image" second cylinder head design would have to be employed.
Another cost cutting excercise.....
Jakes pictures of the twin cam bevel drive engine is very illuminating - it would have taken a Porsche master tech quite a few hours to select, assemble and shim the componants to spec - something that Porsche wanted to get away from when adding up the assembly hours to produce a financially viable car.
Beautiful engine design though - I hate to think what it would cost to manufacture today though :eek:

Here is the front of the EZ30R engine with the chain cover removed, and from what I've read, timing chain failure has not been a problem up to and beyond 100K miles. Jake, I've never seen the 9A1, is it similar in design?

http://i180.photobucket.com/albums/x47/kcpaz/EZ30R.jpg

A million is a big number.

Why did Porsche develop a mass market engine in addition to the older high end design they still use on some cars?

Because they had to achieve a profit or go out of business. Volume and low manufacturing cost lead to profit. Long production runs with the same basic design allow development costs to be amortized over many more units. Same reason the '97 Boxster used the 996's front endparts.

You can hand build a limited number of engines in cars that sell for $100k but not for one that you sell in volume for as low as $40k or even one that sells for $70k.

Quote:

Originally Posted by mikefocke

Nobody said they had to be hand built. I hate to use LS engines as an example again, but look at the entry level versions of that engine. All mass produced using machines and relatively cheap parts. Then there's the higher-end version like the LS7's and LS9's that are hand built with more expensive parts and more performance.

I can't imagine it was a cheap process to design, test, redesign, tool, and manufacture a completely new engine... especially when you consider the cost of revisions (although I'm sure they didn't anticipate the enormous failures of the early motors). I understand parts bin construction, and actually, I think that theory would prove what I'm saying. How would it be more cost effective to have two different engines to manufacture and two different engine assembly systems?

Not only that, but good luck selling a "high-end" German sports car with the mentality of "Well we pinched as many pennies as we could to give you the least expensive thing that we thought we could get away with and still turn a profit". Obviously that's not their marketing strategy, but this seems to be the reasoning a lot of people use to explain things like the M96.

Quote:

Jakes pictures of the twin cam bevel drive engine is very illuminating - it would have taken a Porsche master tech quite a few hours to select, assemble and shim the componants to spec - something that Porsche wanted to get away from when adding up the assembly hours to produce a financially viable car.
Beautiful engine design though - I hate to think what it would cost to manufacture today though

This engine pictured cost 125,000.00 to rebuild and thats fairly cheap.

It takes no less than 16 hours to complete the cam timing procedure as the components must be surface ground for precise adjustment. These engines were produced when a single builder assembled the entire engine, the same way we do the process here under our roof.. No automation, no robotics, nothing less than human hands.

The IMS/Layshaft provides a means of inherent balance for the engine as well

The higher the surface speed of timing chains, the more they will wear and the faster the chain rails that support and tension them will wear. I'll bet that the designers also didn't "master link" these chains, so changing them can prove to be just as near impossible as the M96.

I';ll know all about it when I get the 2010 Cayman engine apart in 2-3 months.