996 Bearing Assemblies Shifting In Engine

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Hello,

Just relaying an experience I have had over the last few months that I thought might be interesting. First time I ever posted anything on the internet so please bear with me, thanks in advance.

Well I have recently taken to rebuilding 996 engines for the Grand Am Koni Challenge Series. I have rebuilt five of them in relatively quick succession and have noticed something I'd like to share for what it is worth.

Before I removed one bolt, a gentleman at a Porsche dealership whom I was discussing my 996 rebuild endeavour with alerted me to some problems I may encounter running these engines. The rear main seal was one, lifters were another, and then he mentioned the possibility of the entire bearing assembly moving inside the case halves. I couldn't believe it but he said they had seen it at the dealership. I planted those seeds in my mind and proceeded to rebuild.

Well, after some rebuilds I got an engine back in which a vibration was reported. I received the engine sans flywheel and I noticed the crankshaft sensor had been cut by ostensibly the flywheel. Inspection of the rear main seal revealed a cranshaft that was not in the center! At that moment I recalled what I had been told and that was that.

Of course upon complete disassembly I found no witness marks to confirm that the bearing assembly had in fact moved. To make an otherwise long story short, the crankshaft broke at the number six rod journal. Broken over two thirds the circumference.

My theory is that the dealer thinks there is a problem with shifting bearing assemblies because they remove engines, see what I saw at first, and then ship them off to Porsche as cores--they don't ever take them apart at the dealer.

Do people really talk about a so called bearing assembly shifting problem? Just thought I'd put it out there. The flywheels are insanely heavey, even the Aasco ones. It was really built well I like to think like the others. I have built many Porsche engines, granted only five 996's, but a broken crank I've only seen once before from Porsche. Only 15 hours on the engine...anyway.

Thanks for reading. Sorry for the bad photo skills.

[AFJuvat]

Welcome to the forum.

Definitely an interesting picture.

Personally, I don't think it is a case of the bearing assembly moving, but more of the fact that the crank, bearing cage, and case are not concentric to each other, unlike the older engines where the bearing journals were actually part of the case.