M96/M97 Engine Failures
Every engine, no matter who manufactures it, suffers from one problem or another. No manufacturer is perfect. Aircooled 911s suffered from broken Dilivar head studs, 2.7s specifically had thermal reactors that made the engines run poorly, and factory rod bolts have been known to stretch. Hindsight is 20/20 - both Porsche and the aftermarket have developed solutions to known issues over time - fixes that are now commonplace and of little concern to owners of vintage Porsche models.
Likewise, the M96/M97 engine has its share of problems. It's been on several lists for possibly the worse engine ever created, but many of the issues we see can be either prevented through preventative maintenance, or at the bare minimum, the likelihood reduced significantly. For well over a decade and thousands of engines later, we're confident the M96/M97 engine found in Boxster, Cayman, and 911 models can and should be rebuilt and upgraded in the case you do have a failure. While some high mileage cars that were rode hard and put away wet might not be worth fixing, many of us, myself included, own a 986, 996, 987, or 997. The question you have to ask yourself is how much money would you spend on a new car that will bring you equal enjoyment compared to say a 1999 Porsche Boxster with a 3.8 liter engine, like what I have. Yes, I have more money in the car than what it is worth, but both in a straight line and in the corners, it's every bit as fast as a much newer GT3. Add in bonded chassis, more electronics, and vehicles that are just that more complex requiring special Porsche testers are just more reasons why the 1997-2008 models are a much friendlier generation for mechanics and DIY guys alike.
This list isn't inclusive, in any particular order, and most certainly isn't intended to scare you into not buying one of these cars or make you hurry to sell yours. You won't find common items listed that can fail on most any modern engine, but specifically those items or failures unique to the M96/M97 engine. The purpose of this list is to make you aware of what possible problems exist and what you can do about it. Like they say, knowing is half the battle. In this case, it's absolutely critical.
Enjoy the Drive!
The Boxster, Cayman, and 911 from 1997 through 2008 utilized a hypereutectic engine block casting technology called Lokasil. It's very similar to its cousin, Alusil, which is also a technology developed by Kolbenschmidt. Alusil is utilized by many European manufacturers and many engines from Porsche have used this casting technology for decades including Porsche 944, 928, 968, as well as Cayenne V8, Panamera V6 and V8, and most recently, 2009 and later Boxster, Cayman, and 911 models with the 9A1 (MA1) engine. Although both Alusil and Lokasil are considered to be hypereutectic, that's where the similarity ends.
Lokasil is what we call "localized Alusil." This is an over simplification, but aptly named. Where with Alusil the engine engine block is cast out of the high silicon content aluminum, originally called Reynolds 390, Lokasil blocks are cast using pre-forms that hold the silicon matrix in suspension in a a resin binder. This binder is infiltrated by molten aluminum in a high pressure die casting process, leaving behind silicon particles suspended in aluminum. At this point, the bores are prepared using a mechanical or chemical process to expose the silicon particles. The oil film on the cylinder bore combined with these silicon particles support the piston/ring/cylinder system. If sufficient silicon particles fracture, the cylinder can no longer support normal operation. The pistons are also iron coated to prevent metal to metal contact, which leads to adhesive wear (scoring), if the coating fails. These failures can occur with any hypereutectic cylinder technology, not just Lokasil.
When we started sleeving blocks with our Nickies sleeves en mass in 2008, most of the cylinder failures we experienced were not bore scoring. But as these cars have gotten older, bore scoring is the number one cylinder failure we see and always on bank two (cylinders 4, 5, and 6). Bore scoring is primarily a problem with the 3.4 (m96.01, m96.02, m96.04, m97.21), 3.6 (m96.03, m96.05), and 3.8 (m97.01) engines found in 911 and Cayman S models (and Boxster S models with the 3.4 m97.22 engine).
Symptoms include oil consumption and piston slap, which is often misdiagnosed as bad lifters. Typically the first symptom is one tail pipe being dirtier than the other. On a 911, that would be the driver's side tail pipe that would get sooty first and the passenger side on Boxster and Cayman models. This typically occurs well before there is any noticeable oil consumption from loss of piston ring seal or abnormal engine noises from the increased piston to cylinder clearance. Once the problem gets really bad, misfires on cylinders 4,5, and 6 will be common, accompanied by oil fouled plugs. The rear bumper cover will also likely have an oil film on it by that point. Engines that are operated for an extended period of time with excess oil consumption noted by oil on the bumper cover and misfires from fouled spark plugs will likely damage the catalytic convertors, requiring them to be replaced.
How can I determine if I have scored bores?
Borescoping and used oil analysis are great tools. Bank two needs to be bore scoped and if possible, checked from the sump with the piston at top dead center (TDC) to check for scoring at the bottom of the cylinder. The reason we recommend this is that scoring starts at the bottom of the bore. Checking through the spark plug with the piston parked at bottom dead center (BDC) may not identify present bore scoring. Used oil analysis is important since we can look for increased aluminum and silicon content - these are indicators of cylinder bore wear in hypereutectic aluminum engine blocks.
So what can you do about it?
We know that oils with elevated levels of ZDDP and moly will help reduce cylinder and piston wear. This is based off of years of independent research with hypereutectic Lokasil and Alusil engine blocks, as outlined in our white paper on bore scoring. Driven DT40 and DI40 (for 2009 and later direct injected engines) have the highest levels of moly found in any street oils, with over 300 ppm of moly. Many have been using LM's Ceratec oil additive to boost moly levels to 300 ppm when added to an A40 approved engine oil.
Overfuelling can wash cylinder bores down and cause cylinder bore scoring. Remember, fuel is not a lubricant. Although lubricity enhancers are used in modern ethanol enriched fuels, these fuels have reduced lubricity compared to ethanol free fuels. Where ethanol free fuels are not available, using Top Tier fuels and ethanol fuel additives like Driven's Defender fuel additives can help with the negative effects of ethanol fuels. Rich running condition can be caused by many variables such as vacuum leaks, faulty mass air flow (MAF) or oxygen sensors, or even bad fuel injectors. Keeping an eye on fuel trim values and recording these values every time you change your oil (which you should be doing every six months or 5,000 miles) can be the first indicator that you have an enrichment issue that might be washing your cylinder bores down. Likewise, taking regular crankcase manometer readings will gauge overall engine health and provide a measure of ring seal, which 4-6 inches of water column is normal for these engines with a healthy AOS. The most common sources of vacuum leaks leading to enrichment are oil fill and aos vent tubes, oil and fuel fill caps, and any plastic engine component subject to aging - plastics contantly exposed to petroleum based products and thermal cycling will over time become brittle and crack. Smoke testing can help isolate the source of these vacuum leaks. Remember, by the time you get a check engine light or malfunction indicator for enrichment, the damage is already done.
On a positive note, we don't see scored bores in 2.5, 2.7, and 3.2 engines found in Boxster and Cayman models.
On a fresh rebuild, overfuelling can cause worn rings and glazed over cylinder bores, requiring that the bores be deglazed or even re-honed along with fitment of new rings to the pistons. Fresh engines, if bore scoped, will exhibit a phenomenon called streaking, which is caused by transfer of piston ring coatings onto the bore during break-in. This is purely cosmetic and does not affect ring seal or oil consumption. However, if engine components including piston rings and bores are not properly cleaned, contamination can cause damage, even to nikasil. Remember, cleanliness is next to godliness. Bore streaking should not be mistaken for bore scoring.
We see many shops and engine builders doing engine rebuilds where they are simply re-ringing the original pistons, solely doing a visual on the cylinder bores for scoring and cracks. Pressure testing plates are not commercially available, so assuming a cylinder isn't cracked is a huge risk when re-using the stock block without being properly reconditioned. More concerning is that most shops do not have the proper tools to check bore surface finishes as well as ovality and taper. The wear limit is 0.08mm, or just over .003", larger than the base measurement. For years we measured blocks when they came in and typically bores would have about .001" of ovality/taper per 20,000 miles, on average, with the worst blocks being out of round by 0.010" to 0.015". This means that most every block needs to be sleeved. If you get a quote for a rebuild and the block isn't being rebuilt, then think hard about what exactly your builder or shop is doing. We have purchased new engine blocks from Porsche over the last decade and the bores measure perfectly round with no taper or ovality (within .0008") when new, so we know they are round to start. New piston rings are round, so if the bores aren't round, then they can't seal up. It may take tens of thousands of miles for them to seat, or never.
Although scored bores are the most prevalent cylinder failure we see, the M96/M97 engine can suffer cracked cylinders. D-chunks failures are most common on 99-01 3.4 996 engines, but all M96 and M97 engines can get intermix caused by cracked cylinders. On the positive side, 2.5 and 2.7 base Boxster and Cayman models seem to be immune from cylinder cracking. Installing a 160F low temperature thermostat and making sure you change the water pump before it fails and you overheat your engine are the two things that you can do to help mitigate this issue.
In the first few years of production of the Boxster and 996, Kolbenschmidt had production issues leading to some blocks to have to be sleeved to fix the bores rather than sourcing a new crankcase. The blocks were bored out and a thin metal matrix composite (MMC) sleeve was used. The sleeve has a small lip at the top (closest to the cylinder head mating surface aka deck) to locate the retain the sleeve. The sleeve can work its way loose and with repeated up and down travel of the piston in the cylinder, the sleeve can fracture at the lip, allowing the sleeve to be pulled down towards the crankshaft. Once this occurs, the piston rings get caught, resulting in the top of the piston being ripped off in the worst case scenario. Most of these failures occur at very low mileages and to be best of our knowledge, it's limited to 986 and 996 models made before model year 2000. Low mileage cars (under 60k miles) were never driven enough under warranty for this to be a problem and have an engine replaced under warranty. When looking at an early car, this, along with rear main seal leaks, were common reasons for engines to be replaced, which can be identified with an AT, X, or Y in the engine serial number.
Just like with slipped sleeves, porous crankcases were isolated to early Boxster and 996 models. Symptoms include oil leaking or weeping though casting surfaces not necessarily located at mating surfaces or where seals or gaskets may have failed. Again, low mileage cars are the ones to worry about since they didn't get driven enough while under warranty for symptoms to present themselves.
The Lokasil engine block used in Porsche Boxster, Cayman, and 911 models requires iron coated pistons. This coating prevents aluminum to aluminum contact between the piston and uncoated aluminum cylinder wall. Just like with Alusil, many incorrectly think the cylinder bores are coated, as in an engine with Nikasil bores, but that is not the case. In a Lokasil or Alusil engine, the cylinder bores are hypereutectic aluminum and undergo a process to expose the silicon particles. The pistons and rings are supported by these exposed silicon particles and the oil film that surrounds them. The piston coating is critical to this system, as without it, you end up with adhesive wear from the aluminum on aluminum contact. The load between the piston skirt and cylinder bore is highest at bottom dead center (BDC), when the piston has to change direction at bottom of the cylinder bore. That's why scoring always starts on the bottom of the cylinder and where piston skirts are contacting the bores. This is also why bore scoping the cylinders from the spark plug with the piston parked at BDC often can hide the evidence of bore scoring.
Although we seldom reuse them, over the years we have inspected many factory pistons. The factory cast pistons found in 2.5, 2.7, and 3.2 models have a much more durable iron coating on them that seldom wears. Likewise, we do not see a lot of wear in the piston ring grooves or collapsed piston skirts. Collapsed skirts can be checked for by measuring the piston 90 degrees to the axis of the piston pins approximately 6 mm up from the bottom of the skirt. A worn or collapsed skirt is one that measure 0.04mm smaller or more than the base measurement within a set of pistons. The piston ring grooves also need to be measured to check for the play between the piston ring and ring groove with no more than 0.15mm of play, verified using feeler gauges placed between the piston ring and ring groove.
The factory pistons also utilize wrist pin offsets. The purpose of the wrist pin offset is to reduce noise, vibration, and harshness (NVH) and also reduce internal friction which increases power. The reduced angularity lowers thrust forces exerted upon the cylinder wall by the piston. However, in the M96/M97 engine, the pistons are not bank specific, meaning the offset goes the correct direction on one bank and the incorrect way on the other. It wasn't until around 2010 that bank specific pistons were introduced in Cayenne and Panamera models. Lack of bank specific pistons has been suggested as a contributing factor to bore scoring in Porsche Boxster, Cayman, and 911 models.
The crankshaft indirectly drives the camshafts via the aptly named intermediate shaft. It also serves to slow down the chains to improve chain life as the M96/M97 engine does not utilize master link timing chains. This means the engine must be disassembled completely to change the timing chains out, if they wear and stretch. The intermediate shaft is different than what is found in aircooled and watercooled Mezger engine in that a sealed ball bearing was used on one end, rather than a plain bearing. But more on this later.
The intermediate shaft has several sprockets that are press fit onto a steel tube. These sprockets are not indexed, keyed, or pinned, which means that these chain sprockets can come loose, leading to a loss of proper camshaft timing and ultimately engine damage. The solution to this is to pin the main drive sprocket that drives the chain that connects the intermediate shaft to the crankshaft. We also check the sprockets and bearing housing bore for runout. Shafts with runout in excess of 0.005" should be replaced to prevent premature chain and IMS bearing failure. Intermediate shafts that have suffered through an IMS bearing failure always have excessive runout and will result in failure of the replacement IMS bearing.
On the side opposite the factory sealed ball bearing, an oil fed plain bearing supports the intermediate shaft. It is fed pressurized oil from the engine oil pump through a small bleed hole, riding in the front console that houses the oil pump. There is a small press fit plug in that end of the intermediate shaft that prevents the oil pump drive from falling into the intermediate shaft tube, which is hollow. Some IMS kits recommend putting a hole in this plug to allow oil to feed their replacement IMS bearing, however this can dislodge the plug, which will result in a complete loss of oil pressure if the oil pump drive disengages from the oil pump. Simply removing the grease seal off the ball or roller bearing when replacing it will allow the engine oil in the sump to properly lubricate the bearing, as the intermediate shaft is located in the bottom of the engine and is submerged in engine oil.
From 1997 to 1999, Porsche use a dual row intermediate shaft bearing which has proven to be as robust as the larger single row used from 2006 through 2008 model years. The Eisen IMS Class Action Lawsuit filed against Porsche revealed the factory Dual Row was much stronger than the Single Row used from 2000-2005. Starting in 2000, Porsche began phasing out the dual row bearing and went to a smaller single row, with significantly less load capacity. From 2002 through 2005, all engines used this smaller intermediate shaft bearing until they went to the larger, third revision for the 2006 model year, which increased the load capacity back to what the original dual row bearing could support. The larger model year 2006 and later bearing also increased the diameter, which increased the bearing and ball speed, further improving the bearing. However, this change has not been enough to resolve the IMS failure issues completely. By far, the single row ball-bearing used starting in model year 2000 through 2005 are the most problematic.
It is not known exactly why these bearings failure, but there are many contributing factors including over-loading. Poor lubrication, long drain intervals, high fuel and moisture content in the engine oil, high oil temperatures, and even operational speeds can affect bearing life. That’s why some bearings last 3,000 miles and others have lasted over 200,000 miles. What we can all agree on is that the IMS bearing must be replaced as part of preventative maintenance. Once the IMS bearing starts to fail or has failed it is too late. The IMS bearing should have had a service interval mandated by Porsche requiring replacement as a wear item, like a timing belt. The sealed bearing also should not have been fitted, as the IMS shaft and bearing is submerged in oil - simply using an open bearing like what is commonly used in gearboxes would have ensured ample splash lubrication from partial submersion. However, a pressure fed plain bearing would have ensured a lifetime of trouble free operation, like that of the IMS bearings in aircooled and watercooled Mezger engines. In fact, the opposite end of the M96/M97 intermediate shaft is supported by a pressure oil fed plain bearing which performs trouble-free, fed oil directly from the oil pump. Replacing the factory IMS bearing with an IMS Solution backdates the engine to use a plain bearing, preventing future IMS issues with the only permanent solution with no moving parts to fail.
It is not commonly known that Porsche did come up with their own bearing update for the most problematic 00-05 Porsche Boxster and 911 engines with the 6204-series ball bearing. It utilizes a ceramic hybrid ball bearing similar to the first and original Classic Single Row IMS Retrofit, however Porsche chose to retain grease seals on the bearing rather than running an open bearing to allow engine oil to lubricate the bearing. However this kit is no longer available for purchase and unfortunately, guidelines for service and installation were not published nor were service intervals. Anything other than an IMS Solution, be it a roller or ball bearing, should have a service interval. All roller and ball bearings will wear subject to the same environmental conditions that contribute to the failure of the original factory bearings.
So what can be done to minimize the
likelihood of an IMS failure? Although a greatly debated subject, most experts
agree that more frequent oil changes every 6 months or 5,000 miles is a good
first step. Secondly, actually driving your Porsche more often and avoiding
higher gears to keep the revs above 2500-3000 rpm is another good step to take
to improve the life of the ball-bearing in the intermediate shaft. Although
there is limited data, the general trend is that lower mileage vehicles with
infrequent oil changes or driven light-footed (as in run at low speed/engine
rpms) are most likely to suffer a failure rather than those cars that are driven
hard and well-maintained. Lastly, use of a high quality motor oil like
DT40 can also provide added protection to all critical engine components beyond
just the IMS bearing.
Along with more frequent oil changes, the addition of a magnetic drain plug coupled with close inspection of the oil filter and magnet at these shorter intervals may help owners identify a failure in its early stages, but later models using the single row bearing can fail with little warning. When inspecting the filter and magnetic drain plug, ferromagnetic debris from the intermediate shaft bearing can be identified easily, appearing like silver glitter. Larger debris than this is indicative of a complete failure. When using the Spin on Filter Adapter & FilterMag, a filter cutter is used to inspect the full flow filter, allowing for visual inspection, which is more reliable than used oil analysis due to the fact that the larger particles generated by IMS wear are not seen by traditional oil analysis.
Early M96 engines utilized an o-ring for the IMS flange seal. The design was revised to use a 4mm wide triple lip seal that provides much better performance compared to the earlier design. The service history of many early vehicles will reflect IMS reseal which involved replacement of the IMS flange with the updated flange and seal, however this is not to be mistaken with replacement of the IMS bearing itself.
The center bolt for the IMS also has an o-ring on it that seals on the center bore of the IMS flange. This o-ring should always be replaced if performing a reseal of the factory flange. One of the major changes when the IMS Retrofit was introduced was the relocation of the inner seal to the flange itself. This eliminated the undercut of the center stud that is the source of many factory IMS failures that result in a large loss of engine oil when it breaks, due to the fact that IMS is submerged in oil.
When you start up the engine, do you hear a rattle or clatter that quiets up after a few seconds, but only on cold start? What you are hearing is chain noise caused by a weak chain tensioner. Some find that by putting a thicker oil in their engine they can reduce the startup noise, but that's not the proper solution. Installing a new chain tensioner (or tensioners) is needed. This is even more important as the rattle at startup is caused by the slack in the timing chains. This can further damage the timing chains and even more importantly, cause false brinelling in the ims bearing caused by these oscillations and vibrations. If in doubt, replace the tensioner for the crankshaft to ims drive chain when replacing the IMS bearing. Better safe than sorry.
There are three chain tensioners on the M96/M97 engine - they are all location specific due to pressure differentials across the engine. Be sure not to mix them up when replacing them. Also, the tensioner for the IMS drive chain has two versions 99610518057 for models up to year 2000 and 99610518056 for model year 2001 and up. The later tensioner is readily identifiable by it's external spring. The early tensioner is for the roller type chain drive crankshaft and IMS and the later is tooth style chain as outlined in this bulletin.
On 1997 through 2002 Porsche Boxster and 1999-2001 Porsche 911 (996) vehicles, a five chain arrangement is used to drive the camshafts. One chain connects the crankshaft to the intermediate shaft, two chains are driven by the IMS out to the heads, then one last pair of chains connect the intake and exhaust camshafts. The 4th and 5th chains are tensioned by the variocam tensioner cylinder and changes tension on the chain connecting the intake and exhaust camshafts, effectively changing lobe centers to provide variable cam timing at specific RPM trigger points. This system is either on or off, whereas the later Variocam Plus provides continuously variable camshaft timing along with variable lift on 3.6 996, 3.6 and 3.8 997, and 3.4 987 engines.
The variocam tensioner cylinders on 5-chain engines have replaceable chain guide rails that are known to wear. If your cam timing deviation is more than 4 degrees, that means these wear pads need to be changed. Porsche revised these wear pads, with the new timing chain rail set for the solenoid actuated Variocam chain adjusters, part number 996 105 253 00, being the correct part to use. You'll need two sets to update your engine. This can technically be done with the engine in the car, but it's easier to drop the engine as the cam covers will need to come off. At that point, it's much easier to change the IMS, AOS, water pump, and all major service items that should be replaced as part of your vehicle's preventative maintenance.
The M96/M97 engine is not a dry sump engine like the Mezger engine used in aircooled 911 and watercooled 996/997 Turbo/GT2/GT3 models. In fact, it has what Porsche calls an "integrated dry sump," which means the engine has a wet sump (oil is stored in the bottom of the engine). The engine utilizes an AOS along with oil defoamers in the sump to control windage and crankcase oil foaming. Each cylinder head is equipped with a scavenge pump that returns oil from the cylinder heads to the sump via interval oil passages (or galleries) through defoamers. This system, when coupled with a Porsche approved N-spec street tire, is adequate to prevent engine damage from occurring due to oil starvation in most driving situations.
Where this all gets thrown out the window is when you start making modifications to the car, like putting sticky tires, stiffer suspension, and other changes that will allow you to pull extended G-forces on track. First mistake people make is they think is that since they aren't racing the car but only doing a driver's education event, that they don't need to take any special precautions. The stock oil system has several deficiencies. Vehicles with the factory X51 power pack featured the "X51 oil baffle" but that wasn't the most important change to the oil system - the kit added a tandem scavenge pump on one of the cylinder heads to aide in scavenging oil trapped in the heads during sustained high g-forces. Although some have converted these engines to dry sump, it's complicated and expensive. Simpler solutions include the addition of an Accusump oil accumulator or deep sump. Although LN still offers an Accusump kit, our 2 quart deep sump which incorporates a modified X51 style oil baffle, anti-slosh tray, and most of all, two extra quarts of oil capacity that all together improve oil pressure during extended high g-force cornering.
With the introduction of the 987 and 997, Porsche updated the oil returns (defoamers) from the 996 swirl pots the oil slingers. They increase the oil flow back to the sump and de-aerate the oil by slinging it against the walls of the sump.
Many don't even bother to change their oil change intervals or increase preventative maintenance. Most, if not all, Porsche clubs require you to flush your brakes before going to the track. What about your engine oil? What many do not realize is that the engine doesn't know any difference between a PCA track day or full on racing. In most cases, race cars are seeing far more frequent maintenance and are being prepared at a much higher level, so it's not these cars I am so concerned with. It's the daily driven cars that are taken to the track on weekends and still only see at most one oil change a year that concern us the most.
What oil being used makes a big deal. You run sticky tires and race brake pads, so why not upgrade your oil. The factory fill is designed to allow Porsche to offer a single product for a global market - something that will work in the Arctic or in Death Valley, but doesn't excel in providing the best possible protection for say, a track event. Besides more frequent oil changes, we believe it's very important to use a race oil if you take your car to the track. Race oils, like Driven's XP9, are formulated with extra anti-wear additives, defoamers, and made to handle the elevated oil temperatures of 300F or more these engines can see on the track. A true race oil will have low detergency, further improving it's wear protection, but also requires that it be changed out at roughly 500 miles of use. A street oil is designed to provide ample detergency to allow for extended drain intervals and corrosion inhibitors that aren't needed in a race oil.
There are three different stroke crankshafts utilized in M96/M97 engines. The 2.5 Boxster uses a 72mm stroke. The 2.7, 3.2, and 3.4 all use a 78mm stroke crank, however the M97.21 and M97.22 engines found in 987 3.4 Cayman S and Boxster S engines have a 78mm crankshaft that uses the larger 3.6/3.8 main journal diameters. Lastly, the 3.6 and 3.8 996 and 997 engines all use an 82.8mm stroke crankshaft. The 72mm crankshaft is very strong and we have not seen many issues with these cracking, but the larger stroke 78 and 82.8mm crankshafts can crack. The reason the 3.4 engine from the Cayman S (and Boxster S) uses the larger main journal diameters is that this increases the overlap between the rod and main journals, greatly increasing the strength of the crankshaft. However, this is still not sufficient to prevent broken crankshafts when these engines are fitted with single mass flywheels.
The reason crankshafts are more prone to cracking with a single mass flywheel is that by eliminating the dual mass flywheel, you are eliminating the vibration dampening capability of DMF. Porsche went as far as to add a harmonic dampening crankshaft pulley in addition to the dual mass flywheel, so they were concerned with harmonics and vibration that can cause crankshafts to crack. In fact, the factory 3.8 pulley can be fitted to any M96/M97 or if you want an underdrive crankshaft pulley, a harmonic dampening underdrive pulley is available from RSS.
The 3.6 and 3.8 crankshaft also went through several revisions with the most current part number 996 102 012 04 being the third and most current revision to increase the strength of the crankshaft with larger radii on the journals, among other changes. When rebuilding any M96/M97 engine, it is critical that the crankshaft is magnafluxed to check for cracks. Skipping this test can lead to catastrophic failure.
Journals can be polished, but if there are deep scratches or gouges, the crankshaft journals should not be turned as Porsche only offers standard bearings. There are aftermarket undersize bearings that require the crankshaft to be cut, weakening it further. Even common repairs using welding have proven not to be durable enough, so replacing a scored crankshaft is the best option. If the thrust surface is damaged or any of the journals have been heavily scored or scorched (blue) due to oil starvation, the crankshaft must be replaced.
Unlike most conventional engine blocks where the main bearing saddles are part of the case halves, the M96/M97 engine is a 3 piece design with a separate crankshaft carrier. What is interesting here is the head studs thread into the crankshaft carrier, not the engine case halves. In fact, the crank carrier is the heart of the engine. The carrier has steel main bearing saddle inserts, with exception of some base model 2.7 engines that used an all aluminum crankshaft carrier without the steel inserts. Typically there are very few issues reported with the crankshaft carrier other than in engines with significant track use where the carrier bolts can stretch and cause fretting of the main bearing saddles. This is easily rectified during an engine rebuild by replacing the stock crankshaft carrier bolts with stronger ARP fasteners. Since the crankshaft carrier is the heart of your engine, we believe every engine can benefit from ARP fasteners here. Oversize bearings are not available from Porsche for the crankshaft carrier nor are specifications or tolerances for the housing bores, so reconditioning the carrier is not possible. Good thing is they are a very robust piece and unless you've had an engine failure like oil starvation, crankshaft, or connecting rod failures, the crankshaft carrier will be reusable during your next rebuild. One of the things that always takes engine builds by surprise is that as you are tightening up the carrier bolts, the crankshaft will become hard to turn and can actually lock up. Don't worry yet - you need to torque all the fasteners to the proper final torque before the crankshaft will free up and spin freely. This is very normal and nothing to be concerned about. Another benefit of using ARP fasteners here is that they are not torque to yield (TTY), so you can safely torque them and still reuse them, where the factory bolts are single use only.
There are some other oddities worth noting. When you disassemble your engine, keep your main bearings and make note of the bearing locator tangs as there are those with left, right, and center tangs, not all of which are available from Porsche. However this is not a problem unless you have had a catastrophic engine failure. In most cases, the main bearings will have no wear and look like new. In instances where new bearings cannot be sourced, we have sent the original ones to Calico Coatings for their CT-1 coating.
Unlike an aircooled Mezger engine, the oil squirters are located in the crankshaft carrier, underneath the main bearings. With the main bearings removed, if you turn the carrier upside down, the squirters will come out easily. In engines that have suffered any kind of engine failure, including scored bores, that has generated foreign object debris should have these squirters replaced. Another big difference compared to aircooled piston squirters is that these have check valves that prevent them from opening if engine oil pressure is below 35 psi, ensuring engines have adequate oil pressure where it's needed. Most importantly, don't forget to put them back in. If you miss even one squirter, the engine will have very low oil pressure and will have noisy lifters among other symptoms like low pressure at idle and across the whole rpm range.
Another big difference with the M96/M97 engine is how crankshaft endplay is set. Most engines use external endplay shims, allowing the engine builder to set the crankshaft endplay after the engine has been assembled. With the M96/M97 engine, there are a pair of thrust bearings that go into the crankshaft carrier on either side of one of main saddles, but only on one half of the crankshaft carrier. Engines from cars with Tiptronic transmissions will never have thrust bearing wear meaning the bearings can be re-used. Engines from cars with manual gearboxes will have varying levels of wear depending on how the car is driven. Deactivation of the clutch start interrupt that requires you to depress the clutch to start the engine is the number one thing you can do to reduce wear on these thrust bearings. Likewise, take the car out of gear at a stop light rather than keeping your foot on the clutch pedal, as this is very hard on the thrust bearings. Failures of the thrust bearing are not common, but do sometimes occur, as we've found them wadded up in the oil pan. When this bearing fails, there is a loss of crankshaft endplay resulting in accelerated rotating assembly component wear and possibly catastrophic engine failure.