Engine Mechanical problem
1991 Porsche 911 6 cyl All Wheel Drive Manual 450000 miles
There is a loud clunk when starting or when turning the engine off. I have heard it on both sides of the motor. It's been suggested that it maybe that the fly wheel is loose. I am just guessing that it may be related to the all wheel drive. Transfer case connections. Just a guess Any idea?
If its a manual transmission then what you likely have is a worn whats called a dual mass flywheel. This flywheel contains a heavy fluid that prevents engine oscillations from transmitting thru the trans. Over time the oil escapes out causing the internal components to hit their end stops, thereby creating the knocking noise. An experienced tech knows how to check for wear. Replacing the flywheel will fix the noise.