gripshifter

Bruce, the 2 engines you had failures on were both from Boxsters not 997s and one of them had close to 200K miles. You also stated that the failure was not due to the IMS and on the other the cause was unknown..

Quote from your very first post on Rennlist in 2013 before you acquired your 997.2:

QUOTE:
Thanx for you help. I am new to this forum as I owned a 2000 S Boxster for 12 years and 197K miles!!! For just some background my 2nd engine failed and that was it for this car. The first engine failed at 47K miles and was covered under warranty .... the 1st failure cause was unknown, the 2nd cause was also unknown but it definitely was NOT the IMS.

Check out my dearly departed 2000 S Boxster at around 175K miles.. note the painted wheels and roof.

My dearly departed car.

Thanx so much
Bruce in Philly

END QUOTE

Lvt19672

BogdanR

True. But an OEM can request a seal material change that would counteract those effects from bearing manufacturers. The problem is what to do with the inventory of already ordered old bearings. On a tight, lean supply chain, things like these may or may not been easily solved.

Not impossible but improbable. All bearing manufacturers use Six Sigma statistical quality control. Such manufacturing defects are quite rare. That's not to say that incorrect fill for this particular application has been calculated to begin with, however, that will result into a whole production run (if not more) of "problem" parts and things like these usually trigger a recall.

You would be amazed to know how much a chain stretches under load and how much take-up chain timing drive systems have to account for in order to keep timing errors under control.

Good design practice has a total system failure mode analysis performed and then tested both in house (durability test benches) and in vehicle, on the field. Known weak spots found on time are usually re-designed but at some point there's a revision freeze in which no other changes will be made in order to be able to ramp up production and launch the product on time. Anything that's not taken care of at the design stage will be assessed for risk of failure then added to the in warranty maintenance cycle of the vehicle or addressed on product "refresh". The problem part in question however has to be made as accessible as possible in order to keep warranty costs down...

People always complain... that's a given but for a product like Porsche, would be nice to know what to prepare for. I bet people would complain less in this case :-)

Bruce In Philly

My point of saying I had two engines blow, was not to pile on the IMS issue or hide something to make a point (I am not sure what point I was really making as I am just frustrated). I am a frequent poster for 14 years now with the same moniker and all frequent readers should know about my engines. My point, albeit a veiled weak one, was expressing frustration at Porsche for making a substandard engine design. I think the IMS is just the most talked about and maybe the most common failure although it appears to get blamed incorrectly sometimes as was my 2nd engine.
All Boxster/Caymen/911 engines are variants of the same fundamental design (except turbo and GT3 as I understand) and suffer from multiple failure modes. And as many old timers have pointed out over and over for the 14 years I have been posting, many of us never remember having engines blow like this, American or German. It is beyond the flattening of the world via the internet, as I know personally folks who had their Porsche engines blow. Back in circa 2003 (?) at Jim Ellis Porsche in Atlanta, I could not believe my eyes when I was in the repair bay and asked the mechanic how common this was.... he just waived his hand and there were literally engines all over the place.... probably 7 or 8.

Unfortunately, wining like I am does not do anything for me or the good folks driving these cars today who hate reading this stuff. But I like many find it fascinating to read about all of the theory, speculation, and some good hard facts about the IMS issue.... my personal conclusion is that it just is a bad design all around from decisions made by accountants trying to save their company.

When Mr BogdanR made his/her original post, I both read it with fascination and a bit of "here we go again". It has been say 12 years I have been reading about this stuff. He clearly posts from a perspective of legitimate authority. But I think what triggered my post was a bit of "why are we analyzing one bearing when there are other modes that destroy this engine". At some point, I look at the whole engine as a system and just conclude the system is weak.

Anyway, my intent was not to challenge Mr/Ms BogdanR, but voice my frustration and fascination in watching engineering meet accounting meet saving a company meet serving a customer meet emotions meet the internet and all of us experts. Interesting...

Peace
Bruce in Philly

wc11

Here's an article in this months PCA-UCR webpage.

http://pcaucr.org/

BogdanR

My "educated" guess is they did find an answer but probably not THE answer we're looking for or we expected.

Along the way it is a number's game. How many exactly have failed compared with the total number of vehicles already sold? Specifically how many warranty affected vehicles are we talking here? These are the questions Porsche had to answer and weigh in their response to the situation. If the problem number is relatively small, replacing engines under warranty while trying to fix an inherent issue with different bearing iterations will be less costly than a recall which will not totally solve the problem anyway. There's a whole inventory of parts waiting to be assembled into engines that have a rather low probability of developing a major problem, the engineering team works on ways of decreasing this probability further and the engine design boys have a new, direct injection powerplant in the works which makes this IMS history.

What would you do in this case? Probably exactly what PAG did... The incidence of problems was not high enough to trigger neither a recall nor a premature end of that engine program.

I'm sorry this issue has affected you so directly. I sure hope I will not be this unlucky...

Cheers!

Bruce In Philly

Marc, you are spot on of course, ..... but......

All parts are not equal. Some parts break, we replace them, and keep on driving. Some other parts break and ......KABOOOM!..... in other words, not all parts are equal.

Take steering linkages/parts. If they were to randomly break, say 5 percent of cars.... that could be quite a few deaths. So, car companies make sure these are designed to a higher specification. Internal engine kaboom parts, while not carrying a death sentence with them, are pretty darn important for serving your customer, maintaining a healthy used market, and preserving your brand reputation. I would think a smart company would work hard to ensure kaboom parts are wee bit tougher than say a coolant tank.

But hey, what do I know. We live in the world of this internet thing and most consumer companies would shoot themselves if they got this kind of bad press for 14 years.... but Porsche just raises its prices and sets sales records..... so who really are the smart guys and gals in this arena?

Peace
Bruce in Philly

BogdanR

Great article WC11. Thanks for sharing!

tbrom

You might try talking with Rabby's tech people; they are the after market bearing manufacturers and they have an idea how long these bearings will last and a recommended service life for one of the ones they produce. I think I remember 50k miles. They do the installs and charge 6k for the 997.1. They are very friendly over the phone. I've talked to them a couple of times.

BogdanR

I’m on the other side of the border but good idea, thanks! :-). I’ll talk to the guys at Autowerks about this on PPI day.

USMC_DS1

+1... I spent a dozen years in product development for the IT industry. The bean counters have a way of compelling management and designers alike to make compromises which make no sense at times... unless you're driven by the quarterly/annual stock holder's meetings.

Porsche's use of larger bearings is a calculated compromise... larger bearings = longer MTBF = fewer in warranty claims. In fact, we've seen very few if any well documented large IMBS failures of the 997.1 (MY06-MY08) to date. Of course, for the few that may fail years from now it will be a costly expensive for the customer to service out of warranty as it will require a full engine tear down to replace the large bearings or worst the entire engine. Such an approach is, of course, likely calculated to minimize the cost to Porsche. Hmmm... my SWAG re MTBF for the larger bearings is a bit north of the 100K miles CPO max warranty coverage so if these blow at all it will likely be around 120K-140K miles perhaps. Odds are most of us will never experience this issue within our ownership time, however, there are many other more immediate and frequent issues to be concerned with such as the water pump, over heating, the Porsche recommend oil change interval(18K miles is way too long), scored cylinder walls, etc.

FWIW, some of us have taken a more preemptive/preventative and more frequent approach towards maintaining our 997.1. For example, I've added additional cooling capacity via a 3rd radiator and an FVD oil pan with increased oil capacity and cooling fins. Use of newly formulated Porsche approved oils, Motul Xcess 8100, vs. MB-1. More frequent oil changes every 3k miles/6 months along with getting an oil analysis from Blackstone. Replacing the WP before it fails... estimated between 40K-50K miles. Properly warm up the engine to operating temp before driving it hard. Shifting at higher RPMs, between 4K-5K as lower RPM shifts induces more load on the engine. Here's some night time reading from an M96/M97 engine rebuild shop out of the UK. May provide you with some additional insight.
http://www.hartech.org/docs/buyers%2...20part%205.pdf

FWIW, my engine has 63K+ miles on it and my oil analysis reports have been clean to date. Frankly the car has been much more reliable and more affordable to maintain than my prior BMW's. Just keep it well maintained and enjoy the ride. Nothing is truly failure proof... even the GT3's and TT's have their own issues. https://rennlist.com/forums/997-gt2-...-registry.html

Charley250

gpjli2

Thanks for sharing this, guy.

Since this post goes over old ground here's a repeat of my 2 cents: switch to a grade 5 full synth oil, double up on factory recommended oil changes, and keep the revs up and the runs long enuff to keep oil hot and clean. Optional but cool: search the literature on Militec-1.

What is good for the engine overall is good for the bearing. Happy driving

Gerry

RollingArt

Welcome to Rennlist Bogdan. Hope you're able to capture that 997 next week.
Always good to hear from an actual expert in the field. Thanks for chiming in. I think you may be a bit fuzzy on this one. The large bearing and the smaller bearing are both spinning at the same rpm. The new larger bearing has larger diameter races. At the same rpm as the smaller bearing, this larger diameter inner race is traveling at a higher speed than the smaller race. Agreed , or am I missing something here?
I believe that it has been established that these IMS bearings were specially made to Porsche's specs and were lubed at the factory with oil and not grease.



Wait a minute, only the bearing is larger. The chain sprocket is still the same size, same chain wrap. Am I missing something here too?

Little history on M/96, M/97 cam chains. The early m96 engines had a five chain layout that saw a lot of wear on the chain guides. In I believe '03 that design was revamped into a three chain layout that has been fairly trouble free. Porsche stepped up and did the right thing here.

Again, welcome to the forum. Looking forward to your input.

BogdanR

No, you’re right. The rpm is actually the same but the ***** are travelling in the races faster. The larger bearing however will have better static and dynamic load carrying capability. This particular layout is an outer ring rotating which is inherently worse for the life of the bearing than an inner rotating ring.

If that is true, it would be the first oil filled bearing I come across in 22 years of engineering.

You’re right again. I’ve just now come across the actual 5 chain layout and corrected the misconception in my mind that the intermediate shaft was acting like a sort of idler. My mistake, I apologize. The rpm will obviously not change, nor the wrap angle which is actually 3 wrap angles. By the look of it, this bearing will bear a good portion of CS and camshaft induced torsionals load. The chain between the CS and the intermediate shaft is short therefore good for controlling timing errors but it’s shortness adversely affects the way cylinder firing torsional loads are getting absorbed by the system. You’d need a well dynamically damped chain tensioner to dissipate all that energy and the hydraulic ones this system use are not particularly good at that. Both IMS and CS bearing will see a lot of high cyclic loading, especially at low/ idle rpm and worst at lugging. I’d venture a guess that, statistically, tip vehicles would suffer less issues then manual ones.

Losing two chains lowers the inertia of the system potentially shifting the 3rd order resonance of the system outside the operating range of the engine. A good thing. Less complexity, less parts to go wrong as well.

Thanks! And thanks for keeping me on my toes :-)