posted on March 19, 2017 14:01
Performance Car Engines That Suck- The Porsche M96
A few months ago we did an article on 5 performance car engines that suck. This story was highly popular, and we have had many requests for more engines that suck. So here we go, in more detail, the next performance car engine that sucks, the infamous Porsche M96 engine.
In 1998, Porsche did a major change to their flat engine line up. Mostly due to tightening emissions standards, they boldly diverted their path from the traditional air cooling to water cooling. Thus was born the M96, Porsche's first flat-6 water-cooled engine.
We didn't really know too much about the M96 until a friend bought a 996 911 for what he thought would be a relatively cheap and reliable track car. Boy was he wrong! During the cars first brisk canyon run days after its purchase, it promptly blew up! Thinking we could help him out, we tore into the engine to find that the M96 is a pretty diabolical nightmare of an engine with many faults, especially the early examples.
Let us show you just how diabolical these engines can be!
The evilest part of the M96 engine is the IMS shaft or more, so the IMS shaft bearing system. The IMS shaft is an intermediate shaft that is driven by a sprocket and chain off of the crank at the rear of the engine that passes through the entire engine and drives one the cams at the front of the engine.
The fact that the engine was designed with such a dumb method of driving the cams is dumbfounding to begin with. Why not drive them just by taking the drive from the front of the crank like any other company would? We think this was done so the same head casting could be used for both cylinder banks. This would save some money but would also add parts and unneeded complexity to the motor, a bad idea.
So we got a sprocket and drive chain for the shaft at the rear of the engine that goes through the entire engine right at the sump level to drive two chains that drive the cams at the front of the engine. WTF! Why is all of that necessary....
Our personal theory is that Porsche previously used intermediate shafts to drive large cooling fans on the top of their engines and with the switch to water cooling, they had to do something with a shaft. That is a joke, well maybe not...
What makes the IMS shaft really dumb is that Porsche didn't use a durable bearing with forced lubrication from the engines oiling system for the shaft. They used a sealed bearing, sort of like a regular industrial bearing, or a skateboard.
The bearing proved to be very underrated for the job. In some cases, the bearing would fail outright. In others, engine oil would penetrate the seals and wash away the grease. With no grease, the bearing would fail. Strangely, failures seem to be more common with cars that are garage queens and sit a lot and cars that are driven gingerly. Cars that are track driven and are driven hard seem to have this problem less frequently.
It seems like about 8-10% of the M96 engines fail like this. In early M96 engines, the failure rate is much higher. These failures have driven down the resale price of old Boxsters and 996 911's and they can be had for bargain prices.
The early engines had bearings that would fail right away. When the IMS shaft bearings failed, the IMS shaft would whip around, damaging expensive stuff. Bearing debris would get circulated around the engine, wrecking havoc and finally the cam drives would fail to let the valves hit pistons. An IMS shaft failure would normally claim everything south of the intake manifold.