beowulf

When I purchased my 40th anniv. 6 years ago (used) I looked into 996's and came across reports of MKI cylinder head cracks....
Per "Total 911" review:

"First, it’s important to point out that it is the early 3.4-
litre engines, made from 1998 to 2000, that are most
susceptible to major failure. The later 3.6-litre engine is
pretty much problem-free. Also, Porsche made many
changes to the 3.4-litre unit over its production life, so the
last of these smaller-capacity engines – made in 2001 –
tend to be more reliable......."

LINK: http://www.autofarm.co.uk/pdf/Total911_July06.pdf

BruceP

I think the picture has changed a bit since 2006. I daresay even Adrian's book would probably benefit from an update. Only now does the entire 996 fleet have enough years and miles under its belt to know anything meaningful.

perfectlap

I picked it up over the weekend for a steal !!!

I just installed it in my living room. Just Needs a little paint.

mrjr1000

What a fantastic array of information.

Boil it all down and the end result is... no matter what year it's a Porsche and as with all other cars, one lives with the good and the bad. We take our chances every time we pull out of the garage.

Choice is still 996 (various reasons) Cab for certain... unless coupe with sun room is just too good to pass up. Exterior red, white, or black... unless any other color is too grand a deal to pass up. Interior cashmere or black... unless grey too fantastic to ignore. For sure 6-speed. That is non negotiable. Now that that is settled:

LET THE HUNT BEGIN!

Cefalu

Funny how people try to put a spin on "facts" to serve their position.

The 2008 911 article started off postulating the early M96 motor was bad because of the IMSB design. We all now know this was an erroneous conclusion. In fact the "improved" design single row IMSB bearings and 3 chain motors were not an improvement. But I am sure they cost less to build. The early 5 chain dual row motors are a more robust design. The issue is so bad with the "improved" motor that even the ceramic bearing upgrade is not considered adequate and a solid bearing is suggested to reduce the IMSB risk. There are those people of course who maintain there is nothing wrong at all with the bearing and ignore the issue completely. Not a risk I would take.

Next, the article launched into cracked cylinder heads and D chunking. I have seen intermix problems and D chunking failures posted here. But it seems to me these issues are not isolated to early M96 motors, nor are they so widespread at this point you could draw any kind of certain conclusions. Hartech makes no distinction. I would say that when the article was written 5 years ago, the newer M96 engines were newer so failures were less frequent on the later M96 motors.

The 911 article addressed weakness in cyl's 2 and 5. This is generally where the ovality occurs, and according to Hartech the 3.4 and 3.6 motors are not showing any material difference as time passes. In fact there is concern over the increased power of the 3.6 which uses the same liner thickness as the 3.4. The 2.5/2.7/3.2 Boxster motors have thicker liners which do not share the 3.4/3.6 propensity to oval. The 3.4 motor was characterized as defective, but the 3.6 follows along with it in this respect.

Hartech goes on to conclude the that 3.6 adds one new problem to the M96 game, cylinder wall scuffing, and Hartech then concludes regarding the increased displacement M96 3.6;

PRIMARY CONCLUSIONS
In conclusion it would seem that the increased piston thrust loads between the piston and the
cylinder bore that has a relatively small amount of hot oil to lubricate it - combined with less
accurate distribution of temperature control inside the engine and higher cylinder temperatures -
has resulted in the more vulnerable side (Bank 2) running closer to critical operating temperatures
and eventually fail in some case where age and other contributory factors separate one example
from another.

ISSUES THAT RENDER THE Cayman S, 3.6 and 3.8 engines different to the 3.4’s and Boxsters.
The head gasket now fits both sides but has larger coolant holes to the cylinder heads, reducing theproportion of coolant to the cylinders and changing their balance that then run hotter.
The connecting rods are shorter increasing cylinder wall loads and friction.
The torque developed is higher increasing piston to cylinder wall loads especially at low revs –increasing friction.
The oil spray jets are the same size as before and therefore the ratio of oil in the cylinders to surface area is reduced.
The space for the coolant to circulate in the cylinders has been reduced.
The crankshaft is wider (reducing any spray oil to the cylinders buy entrapment).

FINAL CONCLUSION.
Although earlier designs didn’t usually suffer this problem – the increases in power output combined with the reduction in cylinder block coolant flow and balance, the direction of the oil spray jets and the quantity of oil present - have pushed the later engines even closer to that limit and as a result some fail when mileages get higher, bore clearances increase, piston coatings wear thin, oil deteriorates, radiators leak, etc, etc – i.e. some engines with some driving conditions – just slightly go over that safe limit for a few seconds and this then results in the scoring we are concerned about.

My take away from the 911 article was it was premature to draw any conclusions between the 3.4 and 3.6 in 2008. They sure got it wrong in the IMSB issue.

Maybe this is why Jake likes the early 996's

beowulf

etwd

[My take away from the 911 article was it was premature to draw any conclusions between the 3.4 and 3.6 in 2008. They sure got it wrong in the IMSB issue.

Maybe this is why Jake likes the early 996's[/QUOTE]


Amen!

5CHN3LL

Comments like this make me love my Oct. '98 build date...

CDLVancouver

Funny how you just did the exact same thing....

I believe that the replacement is adequate as a pm item, but if you are refering to failures of the replaced bearing in the early v late m96 then youre way off. It has been documented here on this forum that those 5 or 6 failures were due to incorrect installations and the like. Not the bearing itself.

KrazyK

There are also other improvements on the 2002+ that make it worth considering.

Cefalu

What I know is what I read from the bearing suppliers. The single row bearing is not as robust as the dual row. There have been many technical discussions here about bearing speed, loads etc. From what I read, the single row bearings have a larger diameter which leads to higher bearing velocities, and force/unit area stresses, than the dual row. I personally think this issue has been raised to a level of hysteria.

And yes, I have heard Jake say that in virtually every failure, the replacement install was done incorrectly and that has led to failures. I don't have a breakout of the replacement failures for single vs double.

Honestly, here I am writing like an expert and all I know is what I read here. But I did actually change my own dual row IMSB myself, successfully I might add, so at least I know where it goes, how it works and what it looks and feels like. Which makes me an expert compared to the majority of people here.

What gets me are the people who spout off how superior the later M96's are based on an old article, when the newer M96's have there own host of issues too.

mrjr1000

With my 2000 Boxster S there was some uncertainty as to whether the IMSB was a single row or double row. From the information I could gather, one could only be certain after removing the bearing or at least inspecting the bearing retainer. Chassis numbers cannot verify which was used.

Is there accurate information regarding when the 5 chain and dual row bearing was replaced with 3 and single for the 3.4 996? Build date? Chassis number?

Also the idea that Porsche would use less quality parts and materials as the "years" progress in a particular model ie 996 seems odd to me. Generally price increases occur MY to MY so to say parts and materials are cheapened to save them money just seems a bit odd to me. I assume improvements as the model years appear. Are these "improvements" only superficial such as headlamp change to appease customer complaints? Please set me straight.

Flat6 Innovations

The information regarding which bearing that is employed in a 2000 and 2005 car could not be less accurate. These REQUIRE visual inspection.

As for 3 chain Vs. 5 chain:
All 5 chain 996 engines were 3.4
All 3 chain engines are at minimum of 3.6L

RF5BPilot

My guess is that the variance of reliability from car to car (now affected by its manufacture, how it's been used and how it's been maintained) is far stronger than attempts at generalizations about model years.

Cefalu

The Porsche engineers responsible for making engine design changes are not offering their insight as to why they made the changes they did. So it's pure speculation as to why they made them. Changes are usually made to improve something, bottom line? defective design? list the ways. But as they say, it is what it is.

The BMW M60/62 engine used in 540/740/840i's started off as a 4.0 V8 and featured a dual row timing chain with all steel cog turning points. The M62 was later released in LARGER displacement as a 4.4 liter with a single row timing chain and a plastic idler guide. Do the math. And yes it's a big issue now with single row timing chains sawing through plastic idler guides. next came the variable valve timing (VANOS) version, and boy is that fiasco.

I am very glad I have the first version dual row V8 4.0 version in my 840Ci.