Porsche M96/M97 Bore Scoring issues explained
There are many articles online and various posts in Porsche forums about bore scoring issues and engine failure! While cylinder bore scoring has been an issue on a relatively small percentage of 996 and997 models, it isn’t a universal problem.
How does bore scoring happen?
The M96/97 Crankcases use ‘Lokasil’ Cylinder liners (a flexible but hard-surface metal matrix composite) and 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 & 968 watercooled engines. Another factor in the M96/97’s engine design is the difference in lubrication and cooling. The oil spray and coolant faces the lower side of the cylinders which means the piston thrust on the right side cylinder runs slightly hotter than the left side. This results in the sixth cylinder becoming hotter when thermal and mechanical stresses were applied across the two banks of cylinders. 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 will the wall which causes scarring. In addition, lubrication of the cylinders is also compromised by a two year oil change interval. When fuel and moisture contaminate the oil (due to low mileage short journeys), the oil becomes diluted which results friction between the piston and the cylinder bore walland localised overheating. A full in-depth article on this issue and other export opinions can be found here
Porsche models that could be at risk of bore scoring
All water cooled 911’s Boxster’s and Caymans from 2004 through to 2009 are at risk of suffering from bore score however, it would appear the percentage of engines actually affected is relatively low.
“Porsche GB advise 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 per cent.excerpt: GT Porsche Magazine (above link)
Rear the full discussion on cylinder bore scoring with the M96/M97 Carrera engines in the March 2015 GTPorsche magazine, by Peter Morgan
Bore Scoring Article GT Porsche
Symptoms of Bore Scoring
- A rythmic ticking noise that sounds similar to that of a hydraulic lifter
- One exhaust pipe has more soot than the other
- Increased oil consumption
- Extremely black engine oil
- Pooling of oil within the cylinders
- Aluminum debris found in the oil filter, and engine oil sump.
Factors that make it less likely include a good service history, a healthy cooling system (to reduce the chance of localised 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 in such an urban environment, a diluted oil doesn’t get changed often.
Preventative maintenance
We would recommend an annual oil change for these models especially if you use your car for regular short journeys.
Models that have been well maintained with a good service history and a healthy cooling system will reduce the chance of localised overheating.
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FAQs
The Porsche bore scoring issue is well known among owners, enthusiasts, and mechanics. Porsche models from 1997 through 2008 including the 911, 996, and 997 as well as the Boxster, Cayman, 986, and 987 have all can experience the Porsche bore scoring problem.
How do you stop the bore score on a Porsche? ›
Maintain your fuel injectors – Use a bottle of Driven Injector Defender every other fill-up. We recommend replacing your fuel injectors every 75 thousand miles to eliminate the chance of leaky injectors washing down your cylinders that can lead to bore scoring.
Can bore scoring be fixed? ›
Proper engine maintenance is crucial to minimize the chances of cylinder bore scoring, but if it does occur, LN Engineering's Nickies sleeves offer a permanent solution.
Does 997.2 suffer from bore scoring? ›
Both 997.2 cars and 991.1 cars have scored but no where near the degree of the 997.1/987.1 cars. The mechanism of the latter cars tends to be different (injector issues is one example) and the scoring is generally at much higher miles, and the cost to sort out the latter cars is huge.
Does a 996 turbo suffer from bore scoring? ›
Porsche M96/M97 Bore Scoring
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.
What year did Porsche fix the bore score? ›
IMS was designed out in 09. Bore scoring less likely in the 09-14 model year range (997.2 and 991.1) but still can happen. 2015+ model year (starting 991.2), they used sumibore which pretty much you won't see bore scoring anymore.
What causes bore scoring on a Porsche? ›
During normal operation, the piston and piston rings are supported by the oil film and the exposed silicon particles. If there is a breakdown of the silicon particles, oil film, or piston coating, cylinder bore scoring can occur.
How to avoid bore scoring? ›
Replace or have your fuel injectors cleaned professionally every 75k miles, this sometimes requires removal of the fuel injectors. Every 20k miles, remove and inspect your engine oil sump plate (oil pan), inspect it for any debris and have your cylinder bores checked for any scoring with a Borescope.
Why is 997.2 the best 911? ›
The revised engines of the 997.2 were simpler designs with 40% fewer parts than its predecessor and are known to be reliable. For the 997.2 generation, the standard 3.6-litre 997.2 Carrera engine's power output increased to 345hp, whereas the Carrera S has an output of 385hp from its 3.8 litre flat six unit.
Is Porsche 997.2 a future classic? ›
The year 2023 will be a big one for 997 owners around the world, as it becomes an official Porsche classic.
Porsche 997 bore scoring is a prevalent issue that owners should be aware of to ensure the longevity and performance of their vehicles. By understanding the causes, symptoms, and available solutions, owners can take proactive measures to address bore scoring before it escalates into more significant problems.
Which Porsches suffer from IMS problems? ›
Boxsters, Caymans and 911s from MY1997 to MY2008 are all at risk of IMS bearing failure, with the exception of Turbo, GT2 and GT3 models.
Does the 2.7 Cayman suffer from bore scoring? ›
The 3.4 engine fitted to Porsche Cayman S and Boxster S vehicles is also susceptible to bore scoring. The 2.5, 2.7, and 3.2 Boxster and Boxster S engines as well as the 2.7 engine fitted to base Boxster and Cayman are not known to suffer from scored cylinder bores.
Do Porsche 981 suffer from bore scoring? ›
Although base model Porsche Boxster and Cayman 987.2 and 981 models share similar Alusil engine blocks, we have never seen a case of cylinder bore scoring with these models.
