NP993

Over the past few weeks, my engine has started making a knocking noise that I think is from worn intermediate shaft bearings (my car is a '77 Carrera 3.0. I recently did the top end, but the case has never been split and has 160,000 Km on it, ~100K miles). The noise emanates from the center of the motor, toward the back (fan end), and is a constant clunk-clunk-clunk-clunk sound only detectable at idle. It's not a metallic or tapping sound, such as when you need a valve adjustment--it's more of a "thunk-thunk-thunk," especially detectable if I slow the idle down and reduce other sources of noise. It's detectable inside the cabin of the car, too, and I'm pretty sure it's gotten louder over the past month. I've also heard that Carrera 3.0's had oil pump problems, but this doesn't seem like a bad oil pump. Any thoughts on this situation? How long before I need to address this? What would cause such premature wear? Thanks for any advice.

Steve, 914 guy

I'd be more inclined to think piston slap, even though it sounds like the middle.
The shaft stays pretty well lubricated, I've never seen one worn out, FWIW

911 Guy

I would take a look at the gears of the shaft. Take a chain cover off and give the chains and the int shaft gears a look. You can look at the shaft gears with a mirror as you rotate the crank. Its got to be a chipped tooth or chain damage, I would think. Of course you can only get a look at the chain side of the shaft, but it beats a 100% teardown to to take a peek.
The main hastle of this job will be getting to the chain covers. Youll need to remove the muffler and the rear part of the "pan" that block the chain covers.
Did this happen suddenly, or more over time?
Good luck,