M50TU: Body vibration at varying engine speeds

[theirongiant]

I have a 1993 525i/M, M50 engine, with 207,000 miles on the clock. The engine, transmission, and driveshaft components are all original to the car.

I have noticed some light vibration in the car at varying engine speeds. The car feels like it drives OK, but I wonder if these symptoms are signs of impending component failure:

Here's what I have done so far to test: I park the car, put it in neutral, and *slowly* press down the accelerator to go from idle through 4,000RPM.

From 600RPM through idle, there is no vibration. At 1,000RPM, there is a steady throbbing that is timed to the crankshaft on every 2nd rotation. At 1,500 RPM, it disappears. At about 2,200 RPM, the vibration returns. At 3,500RPM, it disappears again.


Am I experiencing the normal forces of combustion? Are my engine mounts going? Is there something in my driveshaft that might need attention?

[BillionPa]

engine mounts!

its a harmonic amplification of the engines offset rotation, the mounts balance it out. you can also pick up a fluid damper to help offset the rest.

also the flywheel is supposed to help balance it out too, it may be rusting away, changing its weight distribution.

[liquidtiger720]

Hmm....any write up's on how to do motor mounts for the m50/tu?

[Russell]

Think there is. however, I did it on mine. I may have also posted on my experience, not sure.

Even so, Jack up the engine each side at a time just enough to remove the top and bottom nuts, remove and replace mount. Caution, remove bolts on the radiator shroud. I cracked the drivers side top portion of the shroud before I knew this.