M96 and M97 engines have intermediate shaft, the IMS. They are in the 986 and 987 Boxster, the 987 Cayman, and the 996 and 997 Carrera up to 2008. Shaft drives the camshafts through the timing chains, and on the flywheel end it runs in a sealed ball bearing. When the bearing fails, shaft moves, cam timing is gone, valves hit pistons and metal goes through the whole engine. Grit gets to the oil pump before it gets to the filter. Very often first sign is a destroyed engine.
There are three bearings. Double row is in 1997 to 1999 and some 2000 and 2001 engines. Single row is in about 2000 to 2005. Large bearing is in 2006 to 2008 and some late 2005 engines, and this one can not be changed without taking the engine apart. Model year is not enough. Engine number lists are not always right, and many engines were replaced over the years. Replacement engine built from 2006 on has the large bearing, even in a 1999 car. Only sure way is to look, with transmission and flywheel out. 13 mm nut in the center of the bearing cover means small bearing, this one can be changed. 22 mm nut means the large one.
Double row bearing usually sheds metal for a while before it fails, so there is some warning. Single row often goes fast, with little or no warning. In the class action on the 2001 to 2005 cars, about 8% of single row bearings failed already in the warranty years, against about 1% of double row. This is not a lifetime number, and some engine builders say the two failed at similar rate. Every factory IMS bearing can fail, just not at the same rate.
Turbo, GT2 and GT3 have the Mezger engine, no IMS problem there. The 9A1 engine from 2009 has no IMS at all.
Most of them fail with little or no warning, so I watch the timing live on the scan tool. With engine running it shows how far each camshaft is from where it should be, in crankshaft degrees. I read it hot, after a real drive, at idle. On healthy engine the reading holds within few tenths of a degree. When one bank dances back and forth at warm idle and the other bank holds, the bearing is close to dead. Worn bearing lets the shaft wobble on that end, so one chain goes slack and tight. Engines that danced like this came apart with loose bearings close to failing, and by then damage often started already. Don't wait on this one. Park the car until it is checked. Slow drift during warm up is more often the VarioCam pads, and big jumps of 10 degrees or more are usually sensor, bad ground or solenoid, not the shaft. And steady reading does not prove the bearing is good.
High number that holds steady is something else. On 5-chain engines, the 1997 to 2002 Boxster and 1999 to 2001 996, it is mostly worn VarioCam pads, sometimes already on low mileage. On 3-chain engines steady offset can mean the sprocket for cylinders 4 to 6 slipped on the IMS tube. Either way, before IMS job the reading has to be low, because with worn pads the timing can be lost during the job.
When reading moves at idle, or before any IMS job, I do a pre-check. I cut the oil filter open and the media goes under magnet and strong light. Brown plastic is VarioCam pad material. Black pieces can be tensioner or chain pad material, or the seal of the IMS bearing itself. Bearing sheds fine ferrous metal, magnet picks it up, and once metal shows up it is too late for new bearing in that engine. Sump plate comes off too, debris sits there and does not show in the filter. Then fault codes, over-revs, crankcase vacuum, a drive, and borescope for bore scoring. Normal oil analysis misses bigger particles. About 1 in 5 engines does not pass check like this, and new bearing in scored engine makes no sense.
Oil weep at the IMS cover is a warning too, and it is easy to take it for rear main seal. When center stud of the bearing breaks, engine can dump a lot of oil at once. Any leak at the back of the engine I check right away.
Many original bearings come out with grease gone and engine oil inside, even when the seal looks fine. You can not judge this bearing from outside.
Bearing is changed in the car with transmission out. On Tiptronic, engine and transmission come down together. There are three kinds of fix. Better ball bearing, it has to be replaced again every 6 years or 75,000 miles. Roller bearing, by its own instructions it needs replacing every 4 years or 50,000 miles, and it takes much less thrust along the shaft. Or plain bearing fed with engine oil, this one is permanent. Clutch, rear main seal, flywheel bolts and cover seals get done in same job, everything is open anyway, and dual mass flywheel gets tested. IMS is normal work for me on these cars.
On the 2006 to 2008 engines bearing can not come out without teardown. These large bearings fail way less, and I don't take apart healthy engine only for the bearing. When transmission is out for the clutch, I take out the front seal of the bearing, so engine oil gets in. This is a timing job, cams locked, crank pinned, tensioners out, not a quick pick. Center stud O-ring, cover seals and rear main seal get renewed at the same time. New bearing goes in when engine gets rebuilt.
My rule for oil on these engines is every 5,000 miles or 6 months, and every 3,000 miles or 3 months for short trips or cold weather. Broken down oil hurts the IMS and cylinder walls both. Don't let the car sit for months, water in the oil makes bearing life short. And don't lug it below 2,500 to 3,000 rpm.
Also: Porsche service · Bore scoring · Over-rev report · Porsche PPI