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This case study of an M97.01 3.8 engine is follow-up to our Understanding Bore Scoring in Al-Si Cylinder Systems. With knowledge of the wear mechanism of Al-Si engines, we will examine an engine that came to us having suffered an IMS bearing failure of the larger, non-serviceable 06-08 bearing. An IMS bearing failure will normally not damage the cylinder bores or pistons unless the failure occurs at high speeds or if the engine jumps time, causing the pistons to contact the valves, resulting in at a bare minimum, bent valves. In this instance, none of those things occurred. To learn more about the IMS, visit
https://lnengineering.com/products/ims-bearing-kits-for-porsche-m96-97-engines.html
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TECH TIP
If you own a 2006-2008 Porsche Boxster, Cayman, or 911, it's important to have the grease seal removed from the IMS bearing to allow the engine oil to properly lubricate the IMS bearing. Remember, these engines are wet-sump and since the IMS is at the bottom of the engine, it's submerged in oil.
To learn more preventative maintenance for model year 06-08 IMS bearings, visit
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What's interesting about this failure is that the piston skirt coatings are in the process of failing, but the bores have not yet scored to the point that there would have been any symptoms. Without precisely measuring the bores for wear, it is likely that a visual inspection of the bores by an untrained eye might have not identified an in process cylinder failure as there was no scoring or indication of problems with the cylinders. Had the IMS not failed, the engine would have experienced cylinder bore scoring perhaps a few thousand miles later, resulting in the tell-tale ticking noise caused by piston slap. This is coupled with increased oil consumption and typically a single sooty tailpipe, as often cylinder bank two is the first to fail. At this point in the failure, we would have expected increased silicon and aluminum levels in used oil analysis test results. It is also possible that an inspection of the oil filter and sump may have found ferrous flakes of the piston skirt coating, indicating that once the piston coating is compromised, scored cylinder bores are to be expected.
As part of our failure analysis, we took many measurements. Both case halves had approximately .002" variation in height, which is normal for these blocks and something we correct for by resurfacing the block deck during the Nickies sleeving process. The cylinder bores all exhibited similar trumpet shape with center cylinders being the most out of round. Ovality and taper was far beyond Porsche's wear limit of 0.002" on all cylinders, which is common for these Lokasil engine blocks (they are perfectly round with no taper when new from Porsche). Even if this engine had passed a visual inspection, the excessive cylinder bore distortion would have required corrective action before being suitable for engine reassembly. To learn more about the Nickies process, visit https://lnengineering.com/products/watercooled-cylinders-pistons.html
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We also took a look at the cylinder surface finish with our Mitutoyo profilometer to evaluate the cylinder bore surface. The factory specifications for the Lokasil cylinder surface are as follows:
Roughness Average (Ra) 5.91-13.78 µin (0.15-0.35 µm)
Peak Height (RpK) 15.75-27.56 µin (0.40-0.70 µm)
Core Roughness Height (Rk) 7.87-23.62 µin (0.20-0.60 µm)
Groove Depth (RvK) 3.94-27.56 µin (0.10-0.70 µm)
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We've highlighted the results from our cylinder bore surface traces, both in the area of ring travel and below, where the piston rides. According to Kolbenschmidt, the stated minimum for the RpK of 11.81 µin (0.30 µm) for mechanical exposure of Si particles on a new Al-Si cylinder surface. As you can see, the surface finish is out of spec, with cylinder number four being the worst. We could further extrapolate that cylinder four would have been most likely the first to score. This is to be expected as it is always bank two's cylinders that score first in M96 and M97 engines, as mentioned previously.
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Lokasil and Alusil cylinder bore surfaces get smoother as they operate in the ultra-mild wear (UMW) regime, which is described in depth in Understanding Bore Scoring in Al-Si Cylinder Systems. The distribution of exposed, unfractured silicon particles is very important, however this cannot be evaluated with a profilometer - a microscope with 100-150X magnification is required to verify that no more than 30% of the exposed particles are destroyed. That is why it is so risky to reuse an Alusil or Lokasil cylinder or block without proper reconditioning to restore the original surface finish and ensure proper silicon particle distribution. Without sufficient distribution of intact silicon particles and the required depth of exposure for those silicon particles, you can't get enough oil between the silicon particles to lubricate the piston and piston rings. Losing its ability to retain oil, a period of severe wear will result in a rougher cylinder bore surface finish - scoring. The scoring will expand to include the full length of the cylinder sliding surface where the piston and piston rings travel, subsequently resulting in increased oil consumption and piston slap, which is commonly mistaken for noisy lifters.
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Understanding how scoring begins and where is very important to identifying it. Inspecting cylinder bores for scoring with the piston at BDC as witnessed through the spark plug hole does not allow for a proper evaluation. When borescoping an engine with Lokasil or Alusil bores, it is mandatory to scope each cylinder bore from below with piston at TDC, to see the area below ring travel, as it is here that bore scoring will first appear. It is for this same reason that a compression and leak-down test will not indicate scored bores until enough wear has accumulated in the area of ring travel. A visual inspection of the cylinders, as well as the sump and oil filter, is the only way to ensure an engine has not already started to score.
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Want to learn more?
Subscribe to The Knowledge Gruppe's Rennvision YouTube channel for more videos on bore scoring including how to scope your cylinders properly.
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The M96 and M97 engine is known for relatively low oil consumption, with some using little to no oil between service intervals. With no consumption, a good UOA showing that you do not have elevated silicon and aluminum levels, clean tailpipes, and quiet operation, there is a great chance your engine isn't suffering from scored bores. So what can you do to try to keep it that way? As many already know, cold weather operation and short drives are suspected to be the number one culprit, as many of the engines we received in the past came from areas that experience colder weather. Allowing an engine started at or below 32F 10 to at most 30 seconds (below 0 F) to idle lets oil circulate and begin to warm up. Avoid high rpm, keeping it under 3000 rpm). Equally important is not to lug the engine or use full throttle until the coolant has reached full operating temperature. Porsche does not offer a minimum oil temperature in their owners manual or a published number we can refer to, but Mercedes AMG models run in a reduced power mode until oil temperature reaches 68F and some BMW M-series models (S65 engine) state the minimum oil temperature is 175F for maximum output.
More frequent oil changes using an oil high in ZDDP and moly, like DT40 (or DI40 for direct injected engines), can help protect these components from wear. We recommend an oil change interval of 5,000 miles or six months, whichever comes first, for normal driving conditions. Those vehicles regularly operated short distances or started in temperatures at or below freezing should be serviced every 3,000 miles or three months.
As the newest of these models are over 10 years old, we are seeing more Gen 1 987 and 997 3.4, 3.6, and 3.8 models with scoring even from warmer climates. With many plastics aging and becoming brittle, it is critical to ensure you have no vacuum leaks that may be causing the engine to run rich, which washes the cylinder bores down with extra fuel. Smoke testing and looking at fuel trims with a Durametric or PIWIS are both good ways to identify problems that might not cause a CEL, but can slowly cause damage to your pistons, rings, and cylinder bores. With the prevalence of ethanol enriched fuels, we've also seen injector issues that can also cause similarly damaging cylinder washdown. Where ethanol free fuels are not available, use Top Tier fuels and use an ethanol fuel additive. Used oil analysis can also be used to inspect for fuel dilution in the oil caused by any of the above problems, however it is critical that you have the oil tested every oil change, as trend data is needed for your engine to identify if and when a problem occurs.
Unfortunately, some will experience cylinder bore scoring, even if they follow the rules and take all precautions. What is important when you reach this stage is to know what to do. Without the proper inspection tools, it is impossible to properly evaluate the suitability of a Lokasil or Alusil engine block. Most automotive machine shops are not equipped to properly recondition Lokasil or Alusil cylinders, so typically they are only subjected to a visual inspection to look for scratches or irregular wear patterns. Most don't check for ovality and taper, as if they did, one would find the bores in most blocks to be over the wear spec of .002" ovality and taper published by Porsche.
We often encounter blocks that have had single cylinders sleeved, rather than sleeving every cylinder, or blocks that were reused without any corrective action solely because they have no visible wear. Correcting for a single scored bore by sleeving it without consideration for the ovality, taper, and surface finish of the other bores means the other cylinders can, and often do, fail shortly after the engine has been reassembled. Direct plating of the block doesn't address inherent flaws and weaknesses of the block and can result in later cylinder failures, such as cracks. Cast iron or steel sleeves, although quick and easy to install, result in compromises such as reduced performance and thermal issues, and if installed incorrectly, can cause the aluminum block casting to crack and fail. Although the most expensive option next to a new block from Porsche, LN Engineering utilizes billet aluminum NSC-plated sleeves. Nickies maintain the thermal efficiency intended by Porsche while providing a stronger, long wearing, and low friction cylinder bore surface that is proven to last. Don't accept compromises or sacrifice the performance you deserve.
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125 Gladiolus St.| PO Box 401 | Momence, IL 60954
Phone (815) 472-2939 Fax (413) 280-9041
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All logos and trademarks used for product identification purposes only.Porsche ® 356 ® , 911 ® , 912 ® , 914 ®, Boxster®, Cayman®, Panamera® and Cayenne® are registered trademarks of Dr. Ing. H.c. F. Porsche AG.
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