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alex yates
Brands Hatch
Brands Hatch


Joined: 06 Mar 2014
Posts: 14476
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Sat Dec 01, 2018 5:25 pm    Post subject: Reply with quote

Bearing failures. I also have the data where people had them replaced but they stated there was nothing wrong with the original when removed. Out of 132, 29 have been replaced (but 6 of those were the failures shown in the charts).
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2000 Manual 996 C4 Arctic Silver Convertible


 
  
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segart
Spa-Francorchamps


Joined: 28 Jan 2015
Posts: 347
Location: Jersey - Britains South Sea Isle


PostPosted: Sat Dec 01, 2018 8:05 pm    Post subject: Reply with quote

Great work Alex. You should be on wages!
Rick
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Ghianightmare
Monza


Joined: 25 Apr 2017
Posts: 174
Location: Dublin


PostPosted: Sun Dec 02, 2018 1:38 pm    Post subject: Reply with quote

Agree
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alex yates
Brands Hatch
Brands Hatch


Joined: 06 Mar 2014
Posts: 14476
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Sun Dec 02, 2018 2:57 pm    Post subject: Reply with quote

Cap
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PDCC4S
Newbie


Joined: 09 Oct 2017
Posts: 31



PostPosted: Sun Dec 02, 2018 8:18 pm    Post subject: Reply with quote

Evening

2002 996 c4s owned for the last 16 months, 73k miles to date no IMS change car pulls like a train just spent £1700 on various works service & had the car fully checked over, indy report was to have the car insured for an agreed value ( which I done ) so it must be a good one. My indy said if its not broken don't fix it! Happy motoring.

PDCC4S
 
  
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eabeukes
Silverstone


Joined: 30 Jan 2018
Posts: 127
Location: Aylesbury

1999 Porsche 996 Carrera 2

PostPosted: Mon Dec 03, 2018 9:54 am    Post subject: Reply with quote

I've posted my data but just to say that out of all the bearings, it was the *replacement* one that was boderline failure (likely due to poor fitment). All the paperwork says the old bearings were just fine.
Early 3.4 C2, ferrous pistons blah blah.

I assume if they hadnt been swapped they'd still be going strong.
 
  
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NedHan79
Silverstone


Joined: 08 Nov 2018
Posts: 121



PostPosted: Sat Dec 08, 2018 12:38 pm    Post subject: Reply with quote

Mines a 996.1 3.4 c2. 74k and some change. Porsche and specialist history, sevrviced every 2 years though not many miles between most. Mot certificates to back up mileage. No invoices for any major work like ims etc so I’m assuming it’s all original. Nice to see some real world figures. This thread has just lifted a weight off my shoulders as I’m new to the 911 experience and had heard all the horror stories
 
  
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INWB
Monza


Joined: 02 May 2016
Posts: 172
Location: Leicestershire


PostPosted: Sat Dec 08, 2018 12:51 pm    Post subject: Reply with quote

Hi Alex

2003, 64,000 miles C4S

Have had the IMS replaced as I was doing the RMS and clutch and everyone asks "Have you done the IMS bearing" so I replaced it.

Old one was immaculate, no play at all. Total waste of money getting it replaced except for resale purposes.

The garage (Quorn Classics) did have one very tired looking IMS from a 996.1 car but it hadn't failed.

Note: My car has been serviced with oil change every year (except 2008 and 2010) despite having 2 year service schedule.

Thanks for the work.
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Griffter
Monza


Joined: 22 May 2016
Posts: 226



PostPosted: Sun Dec 09, 2018 11:12 am    Post subject: Reply with quote

INWB wrote:


Old one was immaculate, no play at all. Total waste of money getting it replaced except for resale purposes



I speculatively advertised my car over the summer and had two serious enquires. Both long conversations on the phone, all good vibes until “have you had the IMS bearing done?”. No amount of explanation of the evidence, the risk of replacement causing damage or “check it when the clutch is done” gave the assurance they were after. Very frustrating! One guy even said “you’ve explained that really well, are you an engineer?” - but he still wanted £2k off to get it done himself!
 
  
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GMG
Monza


Joined: 07 Jan 2018
Posts: 200
Location: Devon


PostPosted: Sun Dec 09, 2018 12:15 pm    Post subject: ASR- 1995 sl320 R129 Reply with quote

...kind of vindicates my view that unless you're selling a rebuilt one or have had the IMS replaced then values will be impacted...

No amount of reassurance (whatever data is proffered) to prospective buyers will overwhelm concerns harboured about these engines...

I believe IMS,Bore Score and the usual and universal 100k miles phobia will stick with this engine and be reflected in saleabilty and associated value...

One can state that this shouldn't happen but it will ...
 
  
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Chris_in_the_UK
Estoril


Joined: 19 Mar 2014
Posts: 3509
Location: Harrogate


PostPosted: Sun Dec 09, 2018 8:25 pm    Post subject: Re: ASR- 1995 sl320 R129 Reply with quote

GMG wrote:
...kind of vindicates my view that unless you're selling a rebuilt one or have had the IMS replaced then values will be impacted...

No amount of reassurance (whatever data is proffered) to prospective buyers will overwhelm concerns harboured about these engines...

I believe IMS,Bore Score and the usual and universal 100k miles phobia will stick with this engine and be reflected in saleabilty and associated value...

One can state that this shouldn't happen but it will ...


It does not vindicate any view TBH.

The reality is the internet is awash with stuff and that is what people read and believe. Alex has attempted to get some traction on what members on here have experienced and the data is interesting.
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GMG
Monza


Joined: 07 Jan 2018
Posts: 200
Location: Devon


PostPosted: Sun Dec 09, 2018 9:03 pm    Post subject: Reply with quote

...data is one thing...people choosing how to spend their hard earned quite another , as a previous posters experience attests...

Like it or not; this engine has a reputation for fragility;one that naive optimism cannot dispel...

The thing about the internet is that people access it and the thing about people is that they believe what they read...how else do you explain the existence of a The Daily Mail and Brexit ?!
 
  
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Chris_in_the_UK
Estoril


Joined: 19 Mar 2014
Posts: 3509
Location: Harrogate


PostPosted: Sun Dec 09, 2018 9:10 pm    Post subject: Reply with quote

data 'v' experience?

There are plenty of folk who have been 'rinsed' out of money by people suggesting all sorts of repairs to these cars over the years. If you are suggesting that some of those 'experiences' are the basis for your (and others) views then it's a cr@p shoot at best.

As for the naive optimism - you know nothing of me and my background.

I am not sure why you are here or why you post - it could be considered trolling at worst, or are you just a 'self enforced' realist'........
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NedHan79
Silverstone


Joined: 08 Nov 2018
Posts: 121



PostPosted: Sun Dec 09, 2018 9:18 pm    Post subject: Reply with quote

Alex’s data is great. I’ve a 3.4 and his data shows them to be a safer bet than a 3.6 which is first class news for me. But, I like most, wasn’t on here until I had actually bought a car. So the data is only good for current owners
 
  
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GMG
Monza


Joined: 07 Jan 2018
Posts: 200
Location: Devon


PostPosted: Mon Dec 10, 2018 5:52 am    Post subject: Reply with quote

...I post because we don't live in north Korea thus my opinion is as legitimate as anybody's; the fact that you don't like it is irrelevant and my suspicion is that some of those that express hostility towards my posts on this subject (and applaud this data ) own cars with engines that haven't had any remedial work thus drive with their fingers crossed which isn't a terribly scientific approach to the demonstrable issues afflicting these engines; although perversely ironic!
 
  
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Griffter
Monza


Joined: 22 May 2016
Posts: 226



PostPosted: Mon Dec 10, 2018 7:21 am    Post subject: Reply with quote

What I find interesting is that the data shows that the most valuable models (C4S) are the most failure prone. That suggests to me that the market is permeated by fear and irrationality.

More data would enable more robust conclusions.
 
  
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g911omr
Monza


Joined: 29 Sep 2009
Posts: 222



PostPosted: Mon Dec 10, 2018 9:34 am    Post subject: Reply with quote

The fact that these cars have fragile engines is already built into the price.
Interestingly an engine rebuild appears to add very little value. I'd say that the majority of potential buyers wouldn't have a clue about IMS or any of the other potential pitfalls for that matter. If you actually take a look at the number of cars for sale with well north of 100k on the clock it shows that you are more likely not to need a rebuild as a result of IMS failure.
 
  
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bazhart
Approved Trader


Joined: 20 May 2009
Posts: 898
Location: Bolton Lancashire


PostPosted: Mon Dec 10, 2018 12:06 pm    Post subject: Reply with quote

Our experience is that some original bearings were fitted tighter than others into the IMS housing limits and fits always make this possible) and these ground away more "running in" surface imperfections early on when the bearing was filled with grease and this turned some into a type of grinding paste (metallic particles and grease).


The outside of the early bearings have a very thin wall thickness and can easily distort out of round inside their housing and this can alter how nicely they run and how much running in metal they rub off early on.


The seal is relatively ineffective - but gradually the heat made the grease thin (like oil) and it leaked out. The IMS bearing is at a level that the sump oil bath is at and anyway there is a lot of oil being thrown in all directions by the chains and sprockets - so oil was always being thrown at the bearing seal.


Failures seemed depend on fate and whether there was too much grit retained before it escaped out of the seal and before enough oil was forced back in to lubricate it.


Therefore some failed quite early but if they lasted beyond that the seal became more worn and allowed more oil in and that washed out any remaining grit and the bearing could last a very long time.


The first bearings were double row but spec wise not much different to the single row that replaced it (because the double row had less recess area for the balls to run in compared to a single row).


When the bearings are replaced the hole they fitted into has often changed shape and often has "pick up metal" (compaction) on the surface so removal and refitting can result in an even tighter and more out of round fit for the replacement bearing than the original and if it is done while the engine is still together it is difficult to feel if the fit was right on assembly.

Two weaknesses therefore were the fit of the bearing and the resulting metal wear and grease and how quickly one ran out and the oil managed to get in. A further problem is making things worse by trying to fit a replacement in situ.


If the IMS bearing has survived a long time and high mileages the original fit will have been OK and the seal will by now allow more oil in - so they can then last a very long time.


Replacing the bearing in situ can strain the chain, become too tight and even damage the chain runners - so although you get a new bearing - it might not make things better (and bearings are made with different qualities and clearances) but because of the different fits in the housing a very high quality tight bearing may be worse than a lower quality looser one (since the greater clearance of the loser one can accommodate out of round housings better).


However the small single or double row bearings are verging on being marginally too small for the loads applied and the larger replacement bearing takes more loads comfortably and has a thicker outside diameter (so doesn't distort as much on assembly) and seems much longer lasting despite still having a seal and being grease filled from new.


Removing the seal allows more fresh cool oil in and more debris out - so seems to improve things.


We see relatively few IMS bearing failures so hence if it has already lasted high mileage it might be best to leave it unless the engine is stripped when the fit of a replacement bearing can be more easily established or it can be replaced with an IMS with the bigger bearing (and no seal).


Numerous replacements available have better or worse outcomes. Rollers take more radial loads but less axial ones, ceramics can fail because they are too brittle if there are a lot of vibration loads present, a plain bearing is probably best of the same size replacements but requires an oil feed and is therefore more expensive.


The larger ball bearing without a seal - so far seems the best all round compromise to solve a difficult issue technically and in practice at a modest cost (if the engine is stripped) and a plain oil fed bearing (if not).


Baz
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Bluebird911
Nürburgring


Joined: 29 May 2010
Posts: 421



PostPosted: Mon Dec 10, 2018 3:28 pm    Post subject: Reply with quote

Great insight and explanation Baz. Thanks for posting. Seems like it is a luck of the draw, though thankfully relatively rare! Seems there is no right or wrong answer to avoid occurrence, so literally 'fingers crossed and hope for the best' you are not the x% failure affected.

Seems the only 'no brainers' is regards the seal / or oil feed system to maximise oil flow and change the IMSB when being overhauled.

I've got to agree with Griftter though. The 'market perception' is that the 996 has significant weakness in the engine. I would say 50% of people I talk to at car shows and meets - not normally, but including Porsche specific, ask me if I have changed my IMSB and why am I waiting. Many say they wouldn't buy a 996 unless it had been changed.

Perhaps it is the financial consequences of failure that grabs the headlines rather than frequency that fuels the perception...
 
  
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GMG
Monza


Joined: 07 Jan 2018
Posts: 200
Location: Devon


PostPosted: Mon Dec 10, 2018 5:47 pm    Post subject: Reply with quote

...unless you have a spare £10k plus sat doing nothing then it remains my view, despite whatever you take from this data, that anyone would be mad to contemplate buying a 996/7 with the M96 engine without engine work....

I am inclined towards a view that buying a leggy nice condition model which has had some money spent on it in the usual places and then getting the engine rebuild represents an excellent proposition however...
 
  
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