The bearing could fail due to a stud stress and besides It could begin to make a different orbital movement due to steel balls wear. Both things could happen.
That's why I substitute an hybrid ceramic compound balls bearing (with the same size), which is harder and resistant to fail for more than 10 time compared to steel balls.
The bearing support as you could see in the link I posted before, has 12 mm large compared to 8 mm OEM.
After extracting the bearing from the IMS tube we saw that the internal grease was contaminated with wear oil, and the result is well known.
That's why we decided to install the bearing with a single side seal, to allow the oil make a good lubrication task.
Thanks for your reply.
This thread is very interesting
Originally Posted By: Doug Hillary
Hi,
Joaquin - You said this:
"The bearing suffers of a lack of lubrication and finally breaks the balls..."
There are many myths about the M96 engine family. Most IMS issues occurred in the EARLY engine series and Porsche did indeed replace many engines as needed under Warranty
Extensive UOAs conducted in NA around 2002 did not highlight a lubricant problem and all 100 or so lubricants that were Approved and Listed remained so!
This extract note from Autofarm and JZ Machtech in England tells the story. Both Organisations rebuild Porsche engines including the M96
STARTS
All 996 engines have an intermediate shaft that runs the length of the underside of the block and is chain driven from the crankshaft. This, in turn, drives the twin camshafts on each bank of cylinders. At the end of this is a sprocket which turns on a bearing. The sprocket is retained by a small stud that can break, causing the bearing to fail. At first, this manifests itself as a noisy rattle, which turns into a death rattle as the cam chains come off, leading to further internal damage.
Porsche changed the design of this shaft no less than four times during the life of the 996; partly to solve the bearing failure issue, and partly to reduce an annoying rattle on start-up. Later types, therefore, have a larger bearing and a different sprocket designed to mate with a special toothed chain, whereas the earlier ones drove a conventional double chain.
Because of this, it is not possible to fit the later type intermediate shaft to an early engine without also using a later-type crankshaft, which will work with the toothed drive but is an expensive solution. So you have to fit another early-type shaft which may, of course fail again.
However, Autofarm can modify a 997 intermediate shaft with an original-type sprocket to get around the problem.
Both parties are keen to point out that the problems they’ve discussed probably affect five to ten percent of early 996 engines.
In other words, there are plenty out there that are running fine.
ENDS
