Porsche IMS Bearing Failure

#Porsche IMS bearing years affected (and years to avoid)

The IMS bearing failure lives in one engine family: the M96 and M97 water-cooled flat six, 1997 through 2008. That is the 986 Boxster, the 987.1 Boxster and Cayman, the 996 Carrera and the 997.1 Carrera. Every 9A1-engined car from MY2009 on - 997.2 Carrera and Turbo, 987.2 Boxster and Cayman, 981, 991, 992 and the flat-six 718s - drives the camshafts off the crankshaft and has no intermediate shaft at all. The Mezger GT cars built through 2012 do still have one, but it runs in plain bearings and is not affected.

Inside that window the risk is not even. Porsche fitted three different bearings over twelve model years, MY1997 to MY2008. One carries most of the risk. The other two are low-probability wear items.

Caymans get lumped in with early Boxsters, and they should not be. The Cayman did not exist before MY2006, so every 987.1 Cayman, base and S, has the larger 6305 and none of them has a serviceable IMS bearing. The 987.2 Caymans from MY2009 on have no intermediate shaft. Either way, an in-car retrofit is not on the table for a Cayman.

#IMS bearing failure symptoms: noise, metal in the filter, or nothing

LN Engineering states that it is common for an engine with the factory single-row bearing to fail without warning and with no prior symptoms, including no debris in the filter. A car can run normally on one drive and fail on the next.

The two bearings also behave differently. LN and Flat 6 Innovations both report that the dual row tends to shed detectable ferrous debris, and sometimes make noise, well before it lets go, while the single-row 6204 frequently gives no notice. Advice written for one does not transfer to the other.

What a bad IMS bearing sounds like

When it makes noise at all, it is a low rumble, growl or whirr from the bellhousing end of the engine. It tracks engine speed rather than road speed and is usually easiest to hear at a warm idle in neutral. It does not knock and it does not rattle. A failing water pump bearing, a dry idler pulley and a worn alternator bearing all sound close to the same from three feet away, and every one of them is a fraction of the price. That is the point of the belt-off stethoscope check: if the noise survives with the serpentine belt off, the accessories are out of the picture.

Plastic guide debris is easy to mistake for metal. Cut the filter, unroll the media, run a magnet over it. When misfires or cam timing faults show up alongside metal in the filter, debris has usually already been through the oil pump and bearings, and the engine is often past saving.

#Can you drive with a bad IMS bearing?

It depends on what you have found, and the answer runs from tow it home to drive it and plan the work. Four cases cover almost everything.

• Ferrous glitter or metal chunks in the filter or on the drain plug: park it. Have it towed. Every further mile pumps that debris through the rod and main bearings, and that is the difference between an engine a shop can save and one it cannot.
• A rumble from the back of the engine with a clean filter: stop driving it until the belt-off check is done. It may turn out to be a water pump or an idler pulley, which is a cheap afternoon. Finding that out is worth one shop visit, not a road trip.
• A single-row car with no symptoms and a clean filter: drive it. Nothing short of replacing that bearing changes the odds. Cut the filter at every oil change and plan the retrofit for the next time the clutch is out.
• A MY2006-2008 car with the 6305: drive it normally. That bearing cannot be replaced with the engine in the car, LN Engineering puts its failure rate around 1%, and nobody recommends tearing down a healthy engine to reach it.

The reason the first case is worth a tow bill: if the bearing lets go, the engine usually needs a rebuild or a replacement. LN Engineering puts a rebuild at $15,000-$20,000 and up, and a rebuilt engine with upgrades, removal and reinstallation at roughly $30,000-$40,000. Where a given car lands depends largely on whether it let go at idle or at 5,000 rpm. Against those numbers, a tow and an inspection is cheap. If you have found metal, call us at (239) 777-4605 before the engine gets started again.

#IMS bearing replacement cost: 996, Boxster, 997 and Cayman

These are estimates for an independent Porsche specialist, not a quote and not dealer pricing. Porsche never sold a fix for this part, so there is no factory labor operation to quote from; the numbers below are parts plus labor, built on LN Engineering's published average labor time and parts at retail. Members save 5-15% on labor and 10% on parts, so member numbers land under the ones below. Your written estimate, before any work starts, is the number that counts.

Retrofit bearing kit

roughly $700-$1,100 at list depending on the kit; the single-row kit also needs a dedicated extraction tool, rented or bought - check current pricing

IMS Solution kit

roughly $2,100 at list - check current pricing

Clutch, pressure plate and throw-out bearing (parts)

$800-$1,600; more with a new dual-mass flywheel

Time at the shop

usually two to four working days, longer if a kit has to be ordered

What moves the number: which kit you pick, manual versus Tiptronic, and whether pre-qualification turns up bore scoring or worn VarioCam pads. The worst surprise is a car that turns out to have the non-serviceable bearing after the transmission is already on the floor, which is why an unknown bearing gets quoted in two stages.

#IMS bearing failure rate by year, and the class action

Porsche never published a failure rate for the 2000-2005 single-row bearing. The figures that circulate come out of the Eisen class action: plaintiffs' counsel put it around 10% in comments to Sports Car Market, and LN Engineering cites 8%. Treat 8-10% as their estimate, not a manufacturer number.

The 1997-1999 dual row is far lower risk. It is not zero, and dual row does not mean immune: those grease seals are now more than twenty-five years old. LN Engineering estimates the 6305 in MY2006-2008 cars at around 1%.

Read the other way, that estimate means most single-row engines have not failed. That is not an argument against the work. Preventive maintenance always gets done on some engines that would have been fine, and nobody can tell you in advance which ones.

Was there a recall, or just a lawsuit?

Porsche never issued a US safety recall for the IMS bearing. What existed was a class action, Eisen v. Porsche Cars North America, No. 2:11-cv-09405 (C.D. Cal.), filed in November 2011 and granted final approval in January 2014. It covered MY2001-2005 Boxsters built between May 4, 2001 and February 21, 2005 and MY2001-2005 911s built between May 4, 2001 and February 20, 2005, within specified VIN ranges, excluding Turbo, GT2 and GT3. Because MY2005 987 Boxster and 997 production started in 2004, early-build MY2005 cars were in the class.

Note what that leaves out: 1997-2000 cars, MY2001 cars built before May 4, 2001, late-build 2005s, every Cayman and everything from MY2006 on. It reimbursed IMS damage on a mileage-based sliding scale - 100% down to 40% for original and certified pre-owned buyers, 25% for open-market used buyers - up to 10 years or 130,000 miles, and it paid nothing toward preventive replacement. By its own terms that coverage has expired for every car in the class. Do not plan on Porsche paying for an IMS failure today.

Two more points. There is no reason to assume today's older, more often parked fleet fails less than it did during the class-action years. And the idea that Tiptronic cars fail less is not supported; fewer were built, so there are fewer failures to count.

#How a shop diagnoses it

There is no test that predicts an IMS failure. A competent shop can do three things: establish which bearing the car has, find debris that says a bearing is already going, and decide whether the engine is worth retrofitting at all.

1. 01
   Cut the oil filter open, every oil changeFilter cutter, unroll the media, strong light, magnet. Drop the sump plate if anything turns up. The most useful thing anyone does for one of these engines.
2. 02
   Listen at the rear of the engine with the belt offPull the serpentine belt first so the idlers, alternator, power steering pump and water pump are out of the picture, then stethoscope the IMS area. Keep the run short: with the belt off, the water pump is not turning.
3. 03
   Chase every rear-of-engine oil leakA leak written off as the rear main seal can be the IMS flange triple-lip seal or a broken center support stud.
4. 04
   Pull the transmission for positive identificationWith transmission, clutch and flywheel off, measure flange dish depth - 13.34 mm dual row, 19.27 mm single row - or find the 22 mm nut that means the 6305.
5. 05
   Pre-qualify before spending money on the engineFlat 6 Innovations' pre-qualification procedure drops the sump and bore-scopes the cylinders, adding three to four hours. Some engines fail it, and finding that out costs a few hundred dollars instead of a few thousand.

Single row vs dual row: how to tell which IMS bearing you have

• Dual row sealed ball bearing. All MY1997-1999 engines plus some MY2000 and MY2001 cars. Roughly double the single row's load capacity.
• Single-row 6204 sealed ball bearing. Phased in during MY2000/2001, universal by MY2002, used through most of MY2005. This is the problem bearing.
• Larger single-row 6305, non-serviceable. Late MY2005 and all MY2006-2008. Capacity is back at dual-row levels, but Porsche enlarged the bearing without enlarging the flange bore, so it cannot come out without splitting the case.

You will find engine-number breakpoints for the bearing changes published online, including by LN Engineering. They do not all agree, and LN itself says there is no reliable way to confirm the bearing from the VIN or the engine number. Use them to guess, never to decide.

A factory exchange engine is its own trap. A replacement engine carries whatever bearing Porsche was fitting when it was assembled, so an early Boxster with a later exchange engine can have the non-serviceable 6305. Check the engine for an exchange marking and the service records for an engine replacement.

Two tests owners are told to run do not do what they are told they do. The first is spectrographic used oil analysis. LN states it cannot assess IMS bearing health, because the debris the bearing generates is larger than that analysis can identify. Use it for bore scoring and rod and main wear instead.

The second is camshaft deviation. Factory spec is 0 plus or minus 6 degrees crank and it reads easily on Durametric or PIWIS. Flat 6 Innovations has said cam deviation does not show an IMS problem until the bearing is far gone, by which point there is already metal in the oil. It is really a VarioCam wear pad indicator - and both LN and Flat 6 want any deviation over 4 degrees corrected, usually with wear pads on 5-chain engines, before an IMS retrofit is attempted.

#IMS Retrofit vs IMS Solution: which fix to choose

Why the factory bearing fails

The M96 drives its intermediate shaft off the crankshaft by chain, and the cam chains run off the shaft, which slows the long cam chains and helps chain life. To hold cost down Porsche used one cylinder head casting for both banks, and that forced the two cam chains onto opposite ends of the shaft. The front end runs in a plain bearing fed straight from the oil pump and is not the problem. The rear end, at the flywheel, had no oil passage available in the crankcase casting, so Porsche fitted a sealed, grease-packed ball bearing there. It carries most of the shaft's load, including thrust.

1. The grease seal hardens with age and heat cycling. Grease purges into the sump, and the oil that finds its way in is not pressure-fed and not enough. The bearing runs in boundary lubrication, and the water and combustion byproducts a short-trip or long-parked car collects in its oil make that worse.
2. The raceways spall and pit. The single-row 6204 has roughly half the load capacity of the dual row, so it gets there sooner.
3. The bearing sheds ferrous debris, and the factory filter housing bypass sits in the base of the housing where that debris collects, so when it opens it feeds the rod and main bearings.
4. Terminal failure. The shaft loses radial and thrust support, valve timing goes, and pistons can meet open valves.

Two other failures get lumped in with the bearing. The center support stud was machined with an O-ring groove that cuts its cross-section below its own thread diameter, so it can snap and dump oil at the rear of the engine, and the drive sprockets were never pinned to the shaft, so they can slip and lose valve timing on their own.

On a 1997-2005 car with a serviceable bearing the fix happens from outside the engine, with the transmission out. The engine itself does not come apart. What goes back in is the choice.

For MY2006-2008 cars and any late-2005 car with the 6305, there is no in-car retrofit. LN's own recommendation is not to tear the engine down for it: they estimate roughly a 1% failure rate and say proactive disassembly is not recommended unless the engine is already apart. There is a third-party procedure that bores out the flange housing to remove the bearing in the car. LN, which sells competing products, calls that irreversible and says it generates debris. We are not aware of an independent test either way.

A retrofit is preventive work only. LN and Flat 6 are both unambiguous that it will not save an engine whose bearing has already started to fail, and LN has documented replacement bearings failing after being installed reactively into engines that were already making debris.

Worth doing while the transmission is out: clutch, pressure plate, dual-mass flywheel, throw-out bearing and the rear main seal. On 5-chain engines - 1997-2002 Boxster, 1999-2001 996 - VarioCam wear pads often need doing, and LN says they often wear out before the IMS bearing does.

#Buying a 996, Boxster or Cayman: years to avoid and what to inspect

Do not let the IMS scare you off a good car, and do not let a seller wave it away either. The years that carry the most risk are the MY2001-2005 single-row cars. MY1997-2000 dual-row cars and MY2006-2008 6305 cars sit well below them, and a Cayman is what it is, because nothing can be done to that bearing in the car.

On a pre-purchase inspection: cut the filter, bore-scope the cylinders, read cam deviation hot, and record the engine number off the crankcase. If the retrofit has been done, insist on the invoice - a serialized kit should have paperwork, an installer sticker and a date, and a kit with no paperwork is a kit of unknown age. If it has not been done, price it into your offer. Our pre-purchase inspection starts with the free 49-point inspection and an OEM-level scan; the filter cut, bore-scope and hot cam deviation read get quoted before we start.

How to protect the engine you already have

1. Change the oil every 5,000 miles or 6 months, whichever comes first - every 3,000 miles or 3 months for short trips or cold climates.
2. Use the right oil. LN says nothing thinner than 0W-40, which rules out 0W-30, 5W-30 and 10W-30, and to avoid low-SAPS oils because they are short on zinc and phosphorus anti-wear additives. Pick one that carries a current Porsche approval for your engine.
3. Have a shop fit a magnetic drain plug and a full-flow spin-on filter adapter, which does away with the factory housing bypass where debris collects. Use the filter the adapter maker specifies, then cut that filter.
4. Drive it. Keep revs above roughly 2,500-3,000 rpm rather than lugging in top gear, and do not let it sit for months at a time. Cars that sit are more exposed.
5. Consider a chip detector. The IMS Guardian replaces the drain plug with a magnetic chip detector wired to a dash light. It only helps if the bearing sheds metal before it fails, which the single row often does not, so treat it as a backup to cutting filters, not a replacement. Check it is still sold before planning on one.
6. Honor the interval on a replacement bearing. Retrofit kits carry a service life, and an older kit can be well past due - check the current interval with whoever made it.

#IMS bearing DIY: tools, specs and what the job involves

This is a home-mechanic job only if you already own or can rent the tooling, and only on a car with a confirmed serviceable bearing. It is a transmission-out job with the valve timing broken loose, so the risk is not the bearing. It is the engine.

1. Transmission out; clutch, pressure plate and dual-mass flywheel off.
2. Crankshaft locked at TDC, camshafts locked with the 5-chain or 3-chain cam lock.
3. Chain tensioners out, then the IMS flange off.
4. Factory bearing extracted with the IMS Pro tool kit, replacement installed.
5. Flange resealed with a fresh triple-lip seal and center-stud O-ring, new rear main seal, reassemble.

Dual row - flange dish depth

13.34 mm

Single row - flange dish depth

19.27 mm

Non-serviceable 6305

22 mm center nut

Access needed for positive ID

transmission, clutch and flywheel off

Seals to replace on reassembly

IMS flange triple-lip seal, center-stud O-ring, rear main seal

Tooling

IMS Pro kit - bearing puller, 5-chain and 3-chain cam locks, TDC crank lock pin, and an ez-out for the center stud if it snaps. The single-row kit needs its own extraction tool.

Torque specs

take them from the Porsche workshop manual or the kit instructions for your engine - we are not publishing figures we cannot tie to a source

Shop time

10-14 hours, plus 3-4 for pre-qualification

The job is tool-gated, which is fair to ask about when comparing shops. Ask which kit a shop uses, whether they own the cam locks for your engine's chain count, and what happens if the center stud snaps mid-job.

BMW owners have the same preventive-bearing argument about the S65; see BMW S65 Rod Bearings (E92 M3): Cost, Symptoms, Interval.

We are at 950 Milrany Ln in Melissa, and we work on Porsche alongside BMW, Audi, Mercedes-AMG, VW, MINI and Land Rover for owners across McKinney, Anna, Prosper, Celina, Frisco, Allen, Plano and Princeton. Every car gets a free 49-point inspection, and nothing gets worked on without a written estimate, photos and your approval. On an IMS job where the bearing type is unknown, that means approving the transmission-out inspection first; if it turns out to be the non-serviceable bearing, we stop and re-quote. Our repairs carry a 24-month/24,000-mile parts and labor warranty on the work performed, and our terms page spells out what that covers. Call (239) 777-4605.