Porsche M96/M97 Bore Scoring
There are many articles online and various posts in Porsche forums about bore scoring issues and engine failure; if one were to believe what they see online, they’d think it was an endemic problem. The simple truth is that while cylinder bore scoring has been an issue on a relatively small percentage of 996 and 997 models, it isn’t a universal problem.
If you look at the photo gallery below, you will see typical wear and light scoring found in almost every car on the road. This is not a reason to panic, but rather a reminder to take extra care and precautions with your Porsche. Below, we’ll share our feelings on this issue and what you can do to mitigate it or, ideally, prevent it from occurring in the first place.
How Does It Happen?
The M96/97 Crankcases use ‘Lokasil’ Cylinder liners (a flexible but hard-surface metal matrix composite). Due to the layout of the open deck crankcase on 996/997 models, the cylinder banks are not rigidly supported like the first generation 928, 944, and 968 water-cooled engines. Another factor in the M96/97’s engine design is the difference in lubrication and cooling.
The oil spray and coolant face the lower side of the cylinders, which means the piston thrust on the right-side cylinder runs slightly hotter than the left-side. When thermal and mechanical stresses are applied across the two banks of cylinders, the sixth cylinder becomes hotter. This, in turn, causes the sixth cylinder to become slightly oval in shape, causing more friction between the cylinder and the wall, which results in the cylinder lining being rubbed away.
Once the protective cylinder lining is damaged, the cylinder is in direct contact with the wall, which causes scarring. In addition, a two-year oil change interval (DON’T DO THAT!) compromises cylinder lubrication. When fuel and moisture contaminate the oil (due to low mileage short journeys), the oil becomes diluted, which results in friction between the piston and the cylinder bore wall and localized overheating.
Borescope Results For Porsche 911 (Click to enlarge)
Other than cylinders 5 and 6, we’d consider this normal wear on this engine. Cylinders 5 and 6 show some marking, but nothing compared to what would be thought of as severe bore scoring, as noted in the LN Engineering image above. A stuck piece of carbon, other impurities, or a high engine rev on a cold engine might have caused the slight galling present on cylinder 5, whereas cylinder 6 looks like some debris was caught in a piston ring. Dirty engine oil, extended change intervals, or low-quality oil may have also contributed to it.
Additional Reading
A full, in-depth article on this issue and other export opinions can be found here by our friends at LN Engineering –
https://lnengineering.com/products/watercooled-porsche-cylinders-sleeves-and-pistons/bore-scoring/tips-on-how-to-prevent-porsche-bore-scoring.html
Porsche Models Prone To Bore Scoring
All water-cooled 911 Boxsters and Caymans from 2004 through 2009 are at risk of suffering from bore score; however, it appears the percentage of engines actually affected is quite low.
“Porsche GB advised that it sold 9710 E 996s and 997s in the model years 2004-2006. Some very wet-finger-inthe-air guesswork suggests independent specialist rebuilds and OPC warranty replacements combined may have reached 500 engines from that period, which indicates an overall percentage of around five percent.” (Source: GT Porsche Magazine)
Symptoms of Bore Scoring
• A rhythmic noise that sounds similar to that of an exhaust leak
• One exhaust pipe has more soot than the other
• Increased oil consumption
• Extremely black engine oil
• Pooling of oil within the cylinders
• Aluminum debris was found in the oil filter and engine oil sump.
Realize It’s Not The End Of The World
Consider that for an engine that has traveled 60,000 miles; each piston has gone up and down over 300 million times on average, leading to serious damage and, potentially, eventual engine failure if the required preventative maintenance has not been carried out. Slight to moderate bore scoring is not the end of the world or the end of your engine. It may increase oil consumption or provide an occasional puff of smoke at start-up, but in no way does slight to moderate scoring indicate the need for engine teardown. Engines like this might last 30K, 40K, 50K, or even 100K miles before the effects are severe enough to warrant attention. It is something to be aware of, to try and mitigate, but we don’t believe that it deserves the amount of attention that is often focused on it on the internet. Run your car, enjoy it, and don’t worry.
Avoiding This
Factors that make it less likely include a good service history, a healthy cooling system (to reduce the chance of localized cylinder overheating during the warm-up or over-run), and a usage that isn’t inner city or predominantly short journeys (where the engine is always running with a rich mixture and excess fuel can dilute the oil). The 20K/2yr service intervals also haven’t helped with engine life when diluted oil isn’t often changed in such an urban environment.
Preventative Maintenance
We would strongly advise changing your car’s engine oil every six months or 5,000 miles, preferably with oils formulated with increased levels of Moly additives that most oils do not have, which in turn helps to protect the cylinder walls. Doing so will help the oil remain free of contaminants that could lead to Porsche cylinder bore scoring. Models that have been well maintained with good service history and a healthy cooling system will reduce the chance of localized overheating. More frequent oil changes may be necessary if you track your car, drive short distances, or operate the engine in cold climates.
How We Can Help You
The Service Team here at Atlantic Motorcar is well experienced in this issue and others. With over 40 years of European auto specialization, serving clients from the New England areas, we are familiar with the needs of your auto’s special service.
As Maine’s leading European auto specialists, we provide expert-quality services at a fair rate compared to nearby dealerships and specialty shops. If you’re experiencing any of the above-mentioned symptoms in your auto, please call us immediately; we can usually see your car the same day! At Atlantic Motorcar, we’ve developed some very specific procedures and tooling, combined with our expert technicians, to make this otherwise onerous repair a snap.
Finally
If you have questions or if we can help with service on your Audi, BMW, Mercedes, Sprinter, Honda, Infiniti, Lexus, Mini Cooper, Porsche, Volvo, or VW, please contact us. Our team of Service Specialists is here to help with even the newest autos! (207) 882-9969.
Knowing, not just “doing,” that’s the Atlantic Motorcar Center way.
Thanks!
Warmly,
The Atlantic Motorcar Center Service Team