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|3-Series (E36) Chat relating to the BMW 3-Series from 1992-1999. Autodoodad Specific models include: BMW 316i, BMW 318i, BMW 318iS/ti, BMW 320, BMW 323, BMW 320, BMW 324, BMW 325, BMW 328.|
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Originally Posted by utahprez
I spoke to a friend of mine (a factory trained BMW tech) and he said that most likely he didn't throw a rod. He says that the camshaft is made of steel that can distort a lot befor it breaks and he says that most likely my son downshifted from 4th into 1st thinking that he was hitting third. When this happens, the camshaft candistort up to 20 degrees before breaking and it is likely that the intake valve was still fully open when the piston was at TDC...a lethal combo. He says that is is not uncommon for this to happen.
I talked to Bavarian Motor Exchange and they are fixing me up with a long block performance rebuild.
Originally Posted by triggrhaapi
It's highly unlikely that the camshaft twisted. M50 camshafts are forged steel and hollow, which means they are both brittle and fragile. It is highly unlikely that they were twisted. It's rather much more likely that the valve floated (this happens at high RPM when the valvespring can no longer keep up with the rate at which the valve is being depressed by the camshaft and the valve stays open for longer than the desired duration, which can lead to very hard contact with the piston (keep in mind that the force acting on the valve must exceed the tension of the valvespring in order for this to happen, so if the valve made piston contact, it would be with a great amount of force) and that could very easily break the piston itself, shear the wristpin, cause the motor to throw the connecting rod, or any combination therein. the only way that the camshaft would cause the valve to be open at the wrong time is if the timing chain were to break.
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