Cantech Auto Blog

Porsche IMS Bearing Solution Continued…

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A few months back, we talked about a problem which can occur in 1997-2008 Porsche motors: Intermediate Shaft Bearing Failure

This problem is most prevalent in the M96 motors that were installed in the Boxster and 911 Carrera variants. Recently, after purchasing a 2003 911 C2S, a client contacted the shop. Early in his ownership, our client detected a grinding noise from the engine. Aware of the risks associated with an IMS failure, he immediately and wisely shut the vehicle down and had the car shipped to us. After consultation with the client, we advised him that the removal of the transaxle and an inspection of the IMS were necessary. We were not surprised to find a complete mess where there used to be a sealed cartridge bearing.

Enough heat and friction from pitted bearings caused the race damage seen here.

It’s never pleasant having to explain to a client that his vehicle is in need of a major repair. After contacting every reputable engine supplier that we know, we eventually offered the client two options: a factory reconditioned motor from Porsche ($$$) or a full rebuild, performed by us, using new factory parts and the latest solutions for IMS problems ($$). Recognizing the mechanical and monetary advantages of an engine rebuilt to a level which exceeds factory standards, the client opted for a full rebuild with new factory parts by one of our highly skilled and experienced Porsche technicians.

Wheeling away the engine for disassembly to be sent off for cleaning and machining.

Tear down of the motor was swift and without incident. The only damage beyond that of the bearing itself was a cracked timing chain guide, a common side effect of the sudden loss of tension.

The stock tensioner(L) and machined aluminum replacement from LN Engineering(R). It can fail catastrophically when tension is immediately released causing the timing chain to slap against it violently.

During a failure of this type, there is a risk of damage to the intermediate shaft itself. Though this particular shaft looked okay, we do not have the specialized measuring equipment needed for proper inspection. LN Engineering, experts in IMS reconstruction and failure prevention, recommended that we ship the shaft to them for a reconditioning with a much improved three row ceramic bearing and sprocket alignment that includes pins to improve upon the interference fit that is susceptible to slipping (potentially affecting cam timing). The set screw pins are installed at 120° spacing for perfect balance.

IMS Flange and Sprocket
One of three set screw pins used to ensure the IMS sprocket does not twist on the shaft.
Chain driven by crank shaft.

While the intermediate shaft was being reconditioned, the motor was shipped to a Porsche specialist for inspection, measurement, and slight machine work, including a valve job and crank polishing. We sourced the necessary replacement parts during this time, including  piston rings, various bearings, seals, gaskets, torque to yield bolts, a new water pump, timing chains, hoses, belts, and a new clutch and flywheel.

We received the needed parts and supplies within a couple of weeks. After methodically laying out parts and tools to take stock, the true rebuild began. The photos provide some indication of the numerous steps taken in rebuilding an M96.

Cleaned and honed block ready for reassembly.
Cleaned and honed engine bore.
Split crank carrier with new bearings.
Cleaned and polished crankshaft.
Crank carrier assembled with IMS shaft(top) and connecting rods. Note billet chain guide on right side.
Case half with crankshaft.
Fit inspection.
Piston Ring Compressor.
Valve stems and springs.
Intake ports.
Intake valves.
Clear view of exhaust ports, oil filter housing, and oil sump w/ pick up.
Installation of valve cover.
Block is built. Installation of accessories begins.
Oil Cooler
Priming the motor.
Plumbing and Catalysts installed.
Engine in!
IMS Repair complete!

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