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Engine Failures Continued

RMS - Rear Main Seal

Back before cylinder failures and the IMS became a well known problem with the M96 engine, the rear main seal was the number one concern of most owners. Porsche revised the rear main seal multiple times, eventually settling on the PTFE seal, first released under part number 997 101 212 00. The most current revision as of March 2020 is 0PB 105 249. For most engines, the PTFE provides leak free operation as long as it is installed properly using the factory 9699/2 RMS tool that ensures it is installed to the right depth, which as of 2010 was 13mm from the flywheel mating surface to the location of the RMS. When handling the PTFE seal, it is critical that you do not touch the portion of the seal that rides and seals against the crankshaft. Use of a non-Genuine Porsche seal is not recommended.

Products that claim to add more support to the crankshaft by adding another "bearing" falsely claim the weight of the dual mass flywheel is the reason for rear main seal leaks, when in fact engines that have been found to have chronic RMS leaks do in fact leaks because they were improperly machined from the factory, requiring engine replacement to correct this condition. This can be checked for using Porsche Tool 9699/1 or with precision measuring tools to ensure there is no more than 0.3mm of runout between the crankshaft and the housing bore into which the RMS is installed. These measurements need to be taken at four positions: 12, 3, 6, and 9 o'clock. If you have less the 0.3mm of runout, the PTFE seal will function correctly in your engine, even with that heavy dual mass flywheel!

In a perfect world, these cars would have been driven enough while under warranty to have shown symptoms and be identified has having engines that were incorrectly machined. We have even come across owners of vehicles that didn't know their engine was replaced. These cars would have received a replacement engine as indicated by AT, X, or Y in the engine serial number. Unless you are looking at a car with extremely low mileage, coming across one that is incorrectly machined is very low.

Tony Callas, PCA Technical Committee advisor and owner of Callas Rennsport, has documented the RMS in detail in "RMS: Tales of M96 Woe" which is a great read on the subject.


AOS - Air Oil Separator

The air/oil separator, better known as the AOS, performs an important function in the M96/M97 engine, as it is on many other engines. It applies a vacuum on the crankcase and separates the oil from the air/oil mist pumped from the crankcase. The oil is returned to the sump and the air is routed to the intake manifold. The AOS is also critical for engines that utilize low tension piston rings, as vacuum applied to the crankcase helps improve ring seal. As a side note, we can evaluate the overall health of an M96/M97 engine by measuring the crankcase vacuum - 4-6 inches of water column is typical for the M96/M97 engine, which is a measure of quality of ring seal.

When the AOS fails, oil can be pumped into the intake, causing the tell tale smoke screen from the exhaust. In a worst case scenario, the engine can hydrolock as the oil is a non-compressible fluid. Typically this will cause a bent connecting rod but can also cause minor to catastrophic damage to pistons, rings, and crankshaft, just to give a few examples.

The AOS should be considered a maintenance item. It should only be replaced with a Genuine Porsche AOS along with a new AOS vent tube, which can become brittle and crack, causing vacuum leaks.

When tracking your Porsche Boxster, Cayman, or 911, it's also important not to overfill your engine with oil. This causes added windage and oil mist that can overload the AOS, leading to oil consumption, smoking, or engine damage if oil gets ingested by the engine. Follow our guidelines for setting your oil level and run the oil level at the minimum fill indicated on the dipstick or dash. Adding a deep sump allows for increased oil capacity while running the oil level at the recommended level which is about 1/2 a quart lower than full.



Hydrolock, short for hydrostatic lock, is an abnormal condition in any device that compresses a gas. Typically this occurs if and when water gets ingested by an engine, like if you drive the car through deep water (that's why offroad vehicles have elevated air intakes or snorkels). In this case, typical causes for an M96/M97 engine to hydrolock is due to ingestion of oil from a failure of the air/oil separator or if there is coolant intrusion into the cylinder or combustion chamber, which can be caused by a cracked cylinder. Since water or oil is not a compressible fluid, ingestion of these fluids can result in a situation where as the piston approaches TDC, the reaction force from the non-compressible fluid exceeds the maximum stress the engine components can handle, finding the weakest link, which is typically the piston or connecting rod.


Oil Consumption

Normal oil consumption for engines with Lokasil or Alusil engine blocks is normally quite low. Most owners report not having to add oil to their engines between oil services. This is due in part to the very smooth surface finish applied to the cylinders bores. In fact, there is no visible crosshatch in the bores, unlike with Nikasil, that have bores that are equally smooth, but with a visible crosshatch. These bores are finished with a very low roughness average of below 10 microinches, much smoother than the typical finish in cast iron bores of 20-24 micro inches roughness average.

Typically, oil is retained in the valleys - the deeper the valley, the more oil is held in the cylinder honing cross-hatch. Since horizontally opposed engines tend to have oil pool in the cylinders, compared to a traditional V engine configuration, Porsche pinned the second piston ring to prevent it from rotating and to keep it from lining up with the bottom of the bore. As the second piston ring is as much an oil control ring as it is a compression ring, taking this step helps with reducing oil consumption and smoking at startup. The Air/Oil Separator applies a vacuum to the crankcase, further assisting with ring seal.

According to Porsche's Advanced Technical Information bulletin 0402 released 3-26-04 and 0604 released 11-17-06, Porsche advises the maximum value for engine oil consumption for the M96/M97 engine of 1.6 quarts in 622 miles.

As mileage increases in these engines and the bores start to become ovaled, the ability of the rings to conform to the bore diminishes, reducing ring seal. This can negatively affect oil consumption, however when an engine suffers from bore scoring, engines will rapidly start consuming more oil as the bore scoring progresses. We've seen engines come in that are consuming up to one quart in 50 miles, which at that point, the engines have very noticeable piston slap (engine may sound like a diesel), sooty tailpipes, oily bumper covers, and check engine light for stored misfire faults do to oil fouling of the spark plugs. It is also common to see these engines suffer from damage from detonation which can cause broken rings and worn rod bearings. This is caused by buildup of carbon on the piston crowns and combustion chambers, which effectively increases the compression ratio of the engine.

There are other contributing factors to high oil consumption, including but not limited to worn valve guides, weak or failing AOS, overfilling the engine with oil, ethanol enriched and winter fuels, fuel dilution of engine oil caused by leaky injectors, and even which engine oil you use.


Extended Oil Change Intervals

When the Boxster and 996 were first introduced, Porsche recommended a two year or 24,000 mile service interval. Around that time, most European automobile manufacturers were advising similar oil change intervals up to 30,000 miles. As a result, many engines suffered from oil sludging. This isn't caused by the breakdown of the oil, but rather the consumption and breakdown of the additives as the oil is overloaded with contaminants like moisture, unburnt fuel, and combustion byproducts. Cars that get driven infrequently or very short distances are even more susceptible to damage. It is for this reason we highly recommend changing your oil every 6 months or 5,000 miles and suggest installing one of our spin-on full flow oil filter adapters. If you live in an area where cars cannot be driven year round, you should change your oil before putting the car into storage and avoid starting or idling the engine while in storage. Only run the engine when you can take the car out and drive it long enough to get the oil to full operating temperature, which is warm enough to get the oil over the boiling point of water (212F or 100C), to vapor off moisture from the crankcase.


Oil Filter Bypass

Most automakers, Porsche included, have gone to a reusable canister type oil filter arrangement where you change just the filter cartridge. This is fine and all but the filter housing has a bypass valve built into it. Most filters do, which allows the filter to be bypassed if there is too much restriction in the filter. What happens is over time, the spring gets weak and the filter ends up running in bypass at startup. This poses a problem as the bypass is at the bottom of the filter housing and this is where contaminants in the filter settle. So when you start the engine, if the spring is weak, the contaminants are flushed right back into the engine. This is an even larger issue with the M96/M97 engine as they generate quite a bit of ferrous and non-ferrous debris. If you are having an IMS bearing start to fail, this means you can have IMS bearing material freely circulating in your engine, causing collateral damage. In conventional spin on oil filters, the filter is thrown away every oil change, so you always have a fresh bypass spring, ensuring the filter isn't bypassing when it shouldn't.

We've taken a different approach. We manufacture a spin on oil filter adapter (106-01) that converts the cartridge style filter arrangement to use a conventional spin on oil filter. The filter we specify is the Napa Gold 1042 (Wix 51042), which is used in many applications including the 1997-2004 Chevrolet Corvette. The filter is full-flow meaning that it does not incorporate a bypass, ensuring 100% of engine oil is filtered and no debris from the filter can be ingested by the engine.


Oil Pump and Oil Pump Drive

The M96/M97 engine features an "Integrated Dry Sump" which is, in essence, a wet sump engine. It uses a conventional single stage gear type oil pump that supplies pressure to the entire engine and one separate scavenge pump installed in each head to return oil back to the sump. There is a single oil pickup located in the center of the engine in its wet sump. The oil system is fully contained within the longblock and does not have any external oil tanks or coolers. For street use, this setup provides adequate lubrication, however if you plan on tracking the car, changes must be made to the oiling system to prevent failures from oil starvation.

Engines suffering from low oil pressure or erratic oil pressure readings may need a new oil pressure sender (only use Genuine or OEM) and should also have the updated 997 oil pressure relief fitted. The oil pressure relief is easily changed out and does not require removal of the oil pump or disassembly of the engine to change the pressure relief. If the cam covers or engine sump plate have been resealed and too much sealant is used, this too can cause excess RTV sealant to collect in the engine oil pickup screen which can also cause restriction and lead to engine failure.

In the M96/M97 engine, the oil pump is driven off the intermediate shaft using a steel hex drive. This performs flawlessly most of the time, however we have seen several failures of the oil pump drive where it twists and fails, resulting in a complete loss of oil pressure. This is something we've only seen happen on track, but anytime you have access to changing this part, it's a good idea to swap it out for our 4140 chromoly oil pump hex drive (106-11) that is heat treated and shot peened.



Intermix can occur when oil gets into the coolant or coolant into the oil. This can be caused by numerous things including, but not limited to, bad engine oil cooler (heat exchanger), blown expansion plugs (there are several in the heads and engine case), cracked cylinder head, cracked cylinder, failed AOS (some models have coolant running through them), or even failure of the steel core rubberized seal that goes between the case halves for the coolant cross-over.

When an engine suffers from from intermix with oil in the coolant, the entire cooling system must be cleaned to eliminate any oil from the coolant hoses or radiators. If a vehicle sits with intermix for an extended period of time, it may be required to change out the coolant hoses (the oil can cause the hoses to get soft and fail) and radiators. If you do need to change the radiators, CSF offers upgraded aluminum radiators that have larger cores and are more efficient, for not all that much more money than factory radiators.


Water Pump

The most common failure for a water pump is an external leak or worst case, the bearing supporting the impeller fails. If it wasn't bad enough that you might overheat the engine, that's not the biggest thing we are worrying about. As most modern engines use water pumps with composite (plastic) impellers, these impellers are in service 24/7/365 and can become brittle and crack with age or when the bearing failures, the impeller can come apart. These bits of plastic end up in the cooling system where they can become lodged in the coolant passages in the cylinder heads, resulting in cracked cylinder heads. It is for this reason we advise the water pump is changed out every 4-5 years or at most 60,000 miles, whichever comes first.

I know everyone's first instinct is to install a water pump with a metal impeller. We recommend against this. We only will use Genuine or OEM pumps with the plastic impeller. If a pump with a steel impeller is used and the pump fails, it will end up damaging the engine block resulting in a loss of coolant flow when a new pump is fitted, requiring the engine to be replaced. Changing the water pump as part of preventative maintenance is key along with installation of a 160F low temperature thermostat. Equally important is using the proper coolant, distilled water, and the proper lift tool to ensure you don't have any air pockets in your cooling system. We've made this pretty easy and offer a DIY water pump kit for Boxster, Cayman, and 911 models (both 986/996 and 987/997) and also offer the Baum Coolant Vacuum Lift Fill Tool to ensure the job is done right.


Cracked Expansion Tanks

The modern cooling systems are pressurized, allowing for higher coolant temperatures, effectively raising the boiling point of the coolant. Manufacturers are operating engines hotter and hotter for increased thermal efficiency and also to reduce emissions, but these changes aren't always the best for the longevity of the engine. Furthermore, many of the components in and on a modern engine are made out of plastics that, with age, can fail. The coolant expansion tank is one such item. They can crack and the heat seams can fail, resulting in coolant loss and also preventing the cooling system from holding pressure, both of which can cause the engine to overheat. Anytime there are any signs of coolant leaking, as evidenced by buildup of dried coolant on or in the area surrounding the expansion tank, it should be replaced. In fact, anytime we install a new engine in a car, we recommend putting in a new Genuine Porsche, OEM, or German expansion tank. If the bleed valve on the top of the expansion tank is the source of the leak, we still recommend installing a new expansion tank rather than using a repair kit to replace the leaky valve. Lastly, Porsche revised the cooling system operating pressure, so be sure to use the most current ones so your cooling system can operate at the optimum pressure. The most current expansion tank cap is 996 106 447 04 and don't forget, a 2006-2008 987 also has a coolant fill cap, part number 987 106 044 00, that also needs to be replaced.


Cracked Cylinder Heads

The most common issue with M96 cylinder heads are cracks caused by overheating, typically following a water pump failure. Symptoms include intermix and when we ask customers if they had replaced the water pump recently, most will state yes, and most, less than a year earlier. When the water pump impeller fails, bits of the plastic will circulate in the cooling system. Most don't do any harm, but if the debris gets to the heads, it can limit or block coolant flow in the cylinder head, resulting in the formation of a hot spot. That's where the cylinder head will fail and crack. Changing the water pump before it fails as part of preventative maintenance is the best way to avoid this type of failure.

When it comes to fixing the cylinder head, some cracks can be repaired and some can't. We recommend replacing the cylinder head with a known good core that has been pressure tested for cracks, as we've seen mixed results with heads that have had to be welded. Every cylinder head must be pressure tested when it is rebuilt, even if there was no intermix in the engine previously. It is important that whomever you have rebuild your cylinders heads are Porsche experts, experienced in working with M96 and M97 cylinder heads.


Dropped Valve Seats

The VW Type 4 engine, used in Porsche 914 and 912E models, was known to suffer from dropped valve seats, but these types of failures are not common any longer when cylinder heads are fitted correctly with new valve seats. Likewise, 3-chain 3.4, 3.6, and 3.8 engines used in 2002 through 2008 models can suffer from dropped intake valve seats, requiring new ones to be fitted whenever rebuilding these heads. We include the 3.4 Cayman S engines as well since they are fitted with 3.6 cylinder heads. When the seat comes loose, it can come apart, breaking into multiple pieces, damaging the head, chamber, and taking out the valves. A valve seat failure can cause collateral damage to the piston and cylinder wall and in some cases, debris can be sucked into the intake manifold and cause damage to other cylinders. When this occurs, it requires a complete engine overhaul including replacement of the offending cylinder head. It is critical that every 3-chain cylinder head have new intake valve seats fitted by a cylinder head technician experienced with the M96/M97 cylinder head when rebuilding the heads. A three-angle SERDI valve job is a must. Never under any circumstances should you reinstall a cylinder head without at bare minimum checking the guides, doing a valve job, resurfacing the head with a CBN, and installing new valve stem seals.


Worn Valve Guides

Those familiar with aircooled engines know that worn valve guides can cause an engine to smoke and consume oil. Long drain intervals along with low quality fuels and oils can lead to increased guide wear, however most of the M96/M97 cylinder heads we see show very little valve guide wear. This is something a trained M96/M97 cylinder head technician can inspect for and advise if needed. Be sure to use Top Tier premium fuels as the have increased detergents that help prevent intake deposits that can lead to guide wear. More frequent oil changes using a 5w40 rather than the factory fill 0w40 will help reduce oil consumption and provide slightly better protection due to an increase in HTHS (high temp high shear) viscosity.


Freeze plugs

There are freeze (expansion) plugs in the engine case and also in the cylinder heads. When these parts were manufactured, often access is needed for machining that later needs to be plugged. Steel expansion plugs are fitted, however they can, over time, come loose or if anti-freeze is not used in the cooling system, water can freeze and push these plugs out rather than cracking the aluminum castings. In either case, you can end up with intermix of oil and water when this occurs. When rebuilding an M96/M97 engine, it is important to inspect these plugs and replace them if there is any sign of corrosion or pitting. Replacement plugs are available from Porsche. Some cylinder head technicians recommend epoxying over these plugs in the heads or even tapping the passages for thread in plugs to prevent any future intermix. These are all steps that can be taken when rebuilding your engine, but nothing you need to worry about until that point. If you choose to have your engine block direct plated with Nikasil, be aware that the acid etching process can and will damage these plugs and cause them to fail if they are not replaced.


Blown Cylinder Head Gaskets

We list blown head gaskets not because it's a problem, but rather the opposite, we've never seen an M96/M97 engine suffer from a blown head gasket, unless the engine was fitted with steel sleeves. The factory head studs are quite robust and do a great job of ensuring even clamping load on the head gasket. Likewise, the factory MLS (multiple layer steel) head gaskets are silicon coated and are very robust. Even an engine that has been overheated to complete failure due to coolant loss won't blow a head gasket. However, there are some issues with the design of the M96/M97 engine, specifically leaking around the chain box/well area. The sealing surface is very narrow and there are not enough fasteners in this area, so we do recommend that any time you are replacing a cylinder head or assembling the engine, that sealant is applied on both sides of the head gasket in the chain box/well area to reduce the likelihood of leaks.


Blown Camshaft Plugs

If you've had your cam covers resealed and had the camshaft plugs blow out, you know all about this one. If too much sealant is used when installing the cam covers, excess sealant can block an oil passage and cause the plugs to blow out. Fix for this one is simple - use the correct sealant in the correct amount. More is not always better!

If you do need to remove the cam covers, it is critical that the proper camshaft holding tools are used. If you pull the cam covers without these installed, the camshafts can crack and break. Anytime you are working with the cams, be sure handle them with care, especially with the timing ring at the end - it is just pressed onto the camshaft and if bent or dislodged, the camshaft must be replaced.


Bad Lifters

Does your engine have a tick that sounds like a bad lifter? The first question you have to ask yourself is, do I really have a bad lifter. If you have a 3.6, 3.8, or late 3.4 from a 987 Cayman S or Boxster S, you first need to make sure you don't have bore scoring. That said, there are several lifter related issues with Boxster, Cayman, and 911 models with the M96/M97 engine.

Early 5-chain Boxster (97-02) and 996 (99-01) engines utilize the same lifter in both the exhaust and intake location, as do 3-chain Boxster and Cayman engines without variable lift. 2002 and later 3.6 996, 3.6 and 3.8 997, and 3.4 987 engines with variable lift use a special intake-side valve lift switchover that allows two distinct intake camshaft profiles to optimize engine (and emissions) performance.

The single best thing you can do to minimize camshaft and lifter wear is change your oil every 6 months or 5,000 miles and use an engine oil with increased ZDDP and Moly anti-wear additives, such as Driven DT40.

The first cause for camshaft and lifter wear is from extended oil change intervals, which can cause sticky (noisy) lifters. Lifters hydraulically adjust valve lash using engine oil, so contaminated engine oil can cause lifters to not function properly. The biggest mistake someone can do is use any type of engine oil flush product in these engines. This will dislodge years of contaminants that are then directly transported to the lifters. As the lifters only have a single oiling hole (only in, no out), they act like 24 little tiny lifters. If you have an engine that has been poorly maintained, it's best to drop the oil pan to clean any sludge or contaminants and observe shorter oil change intervals with several changes back to back. We had one engine that required six oil changes back to back until the filter and oil did not come out black.

Over the years, many engines have been misdiagnosed as needing to be replaced because the lifters have pumped up and become over-extended, causing the valves to be held open enough that the engine has no compression. This typically occurs if the oil that is in the engine is too thick, especially in cold climates. If this occurs, the solution is to drain and fill with a thinner oil like a 0w30. Once the lifters bleed down, the valves will close and allow the engine to build compression and run! Then switch the oil out for the proper viscosity.

When replacing lifters, Porsche advises that the lifter valley (cradle) is also replaced. There are no specifications for ovality and taper for the lifter carriers, so it is difficult to evaluate them for re-use. We have seen instances where if there is excess wear in the lifter bore, that the added clearance can cause the lifter to seize in the bore, which will cause the lifter carrier to fail and often will also blow a hole in the cam cover. As the cam cover and cylinder head is a matched pair, you can't just replace the cam cover - you have to replace the cylinder head too, making this a very expensive mistake. It's simpler to just replace the lifter cradle (valley) when rebuilding the engine that suffer this easily avoidable problem.

M96.21, M96.22, and M96.24 m-codes are the only engine designations where we see physical camshaft and lifter failures, intake specifically and on cylinder number 1's outboard engine lifter. These failures will generate FOD (foreign object debris) that can cause damage throughout the engine and can also result in bent valves or broken valve springs. Complete engine disassembly is advised when this occurs.

Although the variable lift intake lifters (buckets/followers) are often trouble-free, it is important to inspect them when rebuilding an engine. They can crack across the face between the center variable lift portion and the outside diameter of the face of the lifter body. The variable lift portion can also stick, causing random misfires that can be hard to diagnose as they will often be intermittent unless the lifter gets stuck in the open position.


Failed Fuel Injectors

With the prevalence of ethanol enriched fuels, we are seeing more and more injector failures including poor spray patterns or leaky injectors, both of which can wash cylinder bores down. Remember, fuel is not a lubricant, even less so with ethanol enriched fuels. Since ethanol-free fuels are not available to the majority of consumers, the best we can do is run Top Tier fuels. The reason to use Top Tier fuels is they have added detergents and lubrication enhancers, as well as more stringent testing for moisture content. Besides using top tier fuels, fuel system additives using polyetheramine (PEA) can help keep injectors clean, but these additives do not help with fighting corrosion caused by ethanol fuels. Driven's Defender fuel system additives provide added protection from the damaging effects of ethanol to fuel system components. Porsche has their own fuel additive to protect against damage from ethanol enriched fuels- The Porsche Classic fuel additive is available under part number 00004420602 and for the US-variant under 00004420622.

It is suggested that corrosion of the steel pintle in the injector can lead to injector failures. Unlike ethanol free fuels, those fuels enriched with ethanol have much shorter storage life of a few months compared to a year or more with ethanol free fuels.

Many of the engines we've diagnosed with bore scoring have also had bad injectors in the cylinders that were scored. We've even seen one instance where a shop used a factory shortblock score the same cylinder within 3,000 miles of being put into service because of a bad injector. This is why we recommend new injectors be fitted on rebuilt engines - simply sending them out for cleaning and testing does not guarantee they will not leak or fail after they are installed.

Every owner of a Porsche Boxster, Cayman, or 911 should be checking their fuel trims regularly as an engine that is running rich due will score bores. Likewise, fresh rebuilds that are running rich and washing down cylinder bores, even with Nikasil bores, will cause accelerated ring wear, requiring the engine to be re-ringed to correct for loss of ring seal. That is a fact.


Vacuum Leaks

The most common vacuum leak that will trigger a check engine light is a gas cap. We've all left that one off at one point in our life. They aren't designed to last forever and can even leak if tightened properly. Good thing they are cheap - we usually recommend installing a new one along with a new oil fill cap when installing a new engine.

There are lots of other plastic components and seals that can cause problems as they age. Plastics can get hard and brittle, then crack, and o-rings can flatten or permanently distort, and once disturbed, not seal up again. Intake seals, AOS vent tubes, oil fill tubes, and plenum boots are just a few items that should be inspected and replaced. Smoke testing an engine is an excellent way to find cracks that might be causing vacuum leaks. We recommend doing this anytime you are doing a major service on the engine and it's a must when installing a new engine to make sure you don't have any vacuum leaks that can cause enrichment and lead to cylinder washdown. The engine's ECU has a very large range for adaptation and will use the various sensors on the engine to adjust fuel trims and won't throw a check engine light; fuel trims can be checked using a Durametric or similar Porsche system tester and should be checked and recorded at every service. Vacuum leaks are a silent killer.


Cracked Ignition Coils

When replacing your spark plugs, which Porsche recommends every 4 years or 48,000 miles on Boxster, Cayman, and 911 models, it's important to inspect the coil packs for cracks or carbon tracing and replace them if they are cracked or even if they aren't cracked if the car hasn't been fitted with the 997 style ignition coil pack. Even though there are heat shields installed on 911s, the coil packs do see quite a bit of heat and when driving in the rain or snow, it's easy for water to splash up on these components, causing misfires when they crack. When replacing the coil packs, it's important to use the most current revision of coil pack, part number 997 602 107 03. It is ok to use OEM here or Genuine, but the OEM Beru units come with the longer fasteners required to install the updated coil packs.


Cracked Spark Plug Tubes

On 1997-2002 Boxster and 1999-2001 911 models with 5-chain M96 engines, spark plug tubes should be replaced, not just the o-rings, when replacing spark plugs and ignition coils. They are made out of plastic and can become brittle. If they crack, they will cause a vacuum leak and lead to over-fueling that can wash down cylinder bores and cause engine damage. Stick to OEM or German made here if you don't go with the Genuine Porsche ones (note o-rings are not included with the Genuine and must be purchased separately).


Broken Chain Tensioner Paddle

The crankshaft is connected to the intermediate shaft via a chain. This chain is tensioned with a tensioner blade (also referred to as a paddle) that operates on a fulcrum point. The blade itself is acted upon by a hydraulic chain adjuster to ensure even pressure. The blade has a replaceable wear pad the chain rides against. The blade itself went through several revisions. The first was changing the pressure pin from a mild steel part to plastic; later revisions added reinforcement ribs to the casting as they can break in the mid-point where they are weakest. This was one of the first internal engine components that LN re-engineered to address the weaknesses of the original part resulting in the introduction of the Billet IMS to Crankshaft Chain Tensioner Blade/Paddle (106-10). This can only be replaced with complete engine disassembly.


Broken or Stretched Timing Chains

Some manufacturers use belts that need to be replaced at certain intervals where others use permanent timing chains. The M96/M97 engine uses permanent timing chains that were designed to last the lifetime of the engine, however, these timing chains do have a finite service life. Some manufacturers offer what are called master link timing chains, allowing you to change the timing chain without disassembling the engine. However, master link timing chains are not available for the M96/M97 engine, so engine disassembly is the only option if you have stretched timing chains.

Stretched timing chains are more prevalent on 2002 and later 911, 2003 and later Boxster, and 2006-08 Cayman engines. These "3-chain" engines use a longer chain that wraps around the camshaft sprockets to drive the cams, where the earlier "5-chain" engines used shorter chains that are less prone to stretching.

Long oil change intervals are hard on timing chains; engines that are coked up end up with carbon in the oil accelerate timing chain stretch, caused by wear to the chains components adding up along with entire length of the chain. The simplest thing you can do to extend the life of your timing chains is to change your oil often and if your chain tensioners are getting weak, causing rattle at startup, change them immediately. Continuing to run your engine with bad chain tensioners is accelerating the wear on your chains and your IMS bearing!


Variocam Intake Adjuster Bolt and Camshaft Sprockets

There have been several changes to the torque specs for the variocam intake adjuster bolt (Porsche part number 987 105 254 00) on 3-chain engines. This bolt is torque to yield and should be replaced anytime they have already been torqued. There is also a diamond friction washer that should also be replaced when installing the Variocam intake adjuster. Please be sure to check for the most current torque specification. Some builders have experienced failures caused by this bolt coming loose, so they choose to use loctite when installing this fastener, which is a safe precaution as having this bolt come loose will result in bent valves and will at bare minimum require the heads to come off.

The intake and exhaust camshaft sprockets early on were a two piece design - the drive for the scavenge pump bolted onto the camshaft timing sprocket. This was revised to a single piece design (Porsche part number 996 105 178 54). Anytime you are in the engine and have access to these sprockets, the updated single piece design should be installed. It is also important to note the M6 x 12mm bolts that attach the camshaft to the sprocket are a 12.9 grade fastener (Porsche part number 900 385 041 01), not 10.9 like the rest of the M6 fasteners on the engine, so do not mix these up or use the wrong bolts as they will come loose. Use of Loctite is not recommended on these fasteners.


Cracked Connecting Rods and Stretched Rod Bolts

So what is a cracked connecting rod? Engine Builder Magazine has a great article about this technology. These connecting rods are not truely a forged connecting rod. They are a powdered metal rod. Besides not being rebuildable, they also have about one third the life of a forged connecting rod. Add more power and raise the RPMs (track use) and the weaknesses of the factory rod start to shine through. Add to that the fact that the stock rod bolts can stretch, it's highly recommended that you do not raise the rev limiter (most aftermarket ECU tunes will raise the rev limiter) on a stock engine. Many have even taken it upon themselves to short shift their engines when tracking the car, to prevent a rod bolt failure, and this has proven to prevent these rod bolt issues. If you have a rod bolt stretch, in most cases, you'll have a rod bearing spin and end up with rod knock, if the engine is stopped before it grenades. If the bolt breaks, bearing comes apart completely, or rod breaks, it's all over - you'll likely need a different core engine from which to build an engine. It's the 3.4 Cayman and 3.8 997 engines when tracked that seem to be most prone to catastrophic failures, so understand this when choosing to track a car that has a stock engine (be sure to address oil starvation with the required oil system modifications and use of the right motor oil for track use). This can easily be corrected when the engine is rebuilt - street cars should be fitted with ARP rod bolts (torqued to ARP's specification, not the factory torque) bare minimum and if you think you might autocross or track the car, replace the connecting rods with forged rods. There are several brands of connecting rods available - Carrillo, K1, and Pauter, all of which are far superior to the original cracked connecting rod.


Single and Dual Mass Flywheel

The dual mass flywheel is a critical component in most modern engines and primarily serves to reduce noise, harshness, and vibration (NVH) and separates the engine and drivetrain from torsional vibrations by dampening them. Porsche had issues with crankshafts cracking, even with the dual mass flywheel resulting in the 82.8mm crankshaft to be redesigned two times. Even with these changes, Porsche added a harmonic dampening crankshaft pulley on the M97.01 3.8 engine.

The dual mass flywheel can go bad - anytime you have access to the flywheel, it's critical to use the proper LuK DMF tester to inspect the DMF for proper spring back or replace it when fitting a new clutch is the best option. Fight the urge to install a single mass flywheel - the dual mass is critical to the performance and longevity of your M96/M97 engine. Not only are they not balanced out of the box (they are off by the weight of the missing tooth on the timing ring), but we've seen multiple instances where engines have suffered broken or cracked crankshafts shortly after having been fitted with a lightweight, single mass flywheel. We have also seen numerous engine failures on track where lightweight flywheels have been fitted, even with a deep sump or race oil due to the extra heat transfer through the aluminum single mass lightweight flywheel into the rearmost main and rod bearing. Long story short - use an OEM LuK or Genuine Porsche dual mass flywheel along with an OEM SACHS, SACHS Performance (organic lining), or Genuine Porsche clutch. We've had no clutch slippage issues reported with even the stock clutch and pressure plate, even on performance builds.

Some claim that the weight of the dual mass flywheel is the reason why the rear main seal leaks. This is completely false. Porsche realized they had a problem where the crankcase was incorrectly machining, causing the rear main seal to leak. This can easily be inspected for using Porsche Tool 9699/1 or with precision measuring tools. There should be no more than 0.3mm of runout between the crankshaft and the housing bore into which the RMS is installed when measured at four positions: 12, 3, 6, and 9 o'clock. Porsche also revised the rear main seal several times, resulting in the most current PTFE seal which is proven to prevent rear main seal leaks if your engine is properly machined, even with the added weight of the dual mass flywheel.


Power Steering Pump

The M96/M97 engine is known to have issues on track due to oil starvation, however the power steering pump can also cause problems. Depending on driving style, specifically sawing of the steering wheel to help increase front end grip, coupled with the power steering pump that can be overdriven at high engine speeds experienced on track, elevated power steering fluid temperatures can cause the reservoir to melt. The resulting loss in power steering fluid can cause an engine fire, so some racing classes allow electric power steering pumps and all races classes, even stock classes like Spec Boxster, Spec 996, or Spec Cayman, allow for the addition of power steering coolers and underdrive crankshaft pulleys.


ECU Tuning Software and Cold Air Intake

Many owners are looking for easy horsepower and a cold air intake coupled with an software flash of the ECU can be attractive. In our experience, the majority of cold air intakes will increase intake air temperatures (IAT), resulting in reduced engine performance, albeit more intake sound being transmitted to the interior by these aftermarket intakes- it just sounds faster. The factory airbox has proven itself time and time again the most efficient. For the 911, the 3.8 airbox is the king - making the most horsepower, even with a paper filter. On early Boxsters, the later 987 airbox can be fitted to the vehicle when taking your 3.2 to 3.8 liters, ensuring the engine can breath. In fact, the 987 airbox is the same on the 987.2 with the MA1 engine and we learned years ago it flowed enough to even support Flat 6 Innovation's Cayman X 4.2 liter engine. It's hard to improve in this area over what Porsche supplied.

With regards to ECU tunes, we use them all the time on 987.2/997.2 and later engines, regularly installing Cobb Tunes on these vehicles. The difference with these engines compared to the M96/M97 is that they don't have anywhere near the number of issues, specifically with rod bolts, that we have to worry. Most ECU tunes will raise the rev limiter, further stressing the stock connecting rod bolts on the M96/M97 engine. Some tunes also will lock out adaptation or turn off monitors that can prevent a check engine light from coming on if there is a problem with your engine. Do your homework before purchasing an off the shelf tune for a stock engine, especially if you track your car.


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