Question about balancing rotating assembly

gregcon said

I'm not suggesting no one knows anything...I'm just saying that we all know less than we'd like to think. I do believe there is an impressive base of knowledge 'in the world'...but mostly it exists behind closed doors in places that have the chops to create it. Lexus, Ilmor, GM, etc. Sometimes that information leaks out in one form or another and we get to get little nibbles of it.

Harmonics? I dunno. When they first brought out the V10 in Ram trucks, they had an failure point where the harmonic damper would wobble loose. The blame, according to Dodge, was driveline harmonics. I take that mean the engine itself was happy but when you bolted it to the rest of the driveline, it got unhappy.

Click to expand...

The damper is there to help absorb/soak-up the crank torsional vibrations (the much higher frequency twisting vibrations in the crank), and has to be VERY firmly clamped to the crank snout to do that. Again, not addressed in balance work but in the inclusion of a damper.

In your V10 story, the crank was actually not 'happy' without the damper. It is very 'unhappy'. The damper was designed in from the get-go to make it 'happy'. The damper fastener worked loose for some reason; it could have been a weak or undersized fastener, too thin a clamping washer, too low an installation torque, or several other reasons. That is why on the SBM and BBM, you have a BIG bolt in the crank snout, with a THICK washer used, and it is torqued to 135 ft lbs. That is all done to clamp the damper HARD to the crank, so that the damper can effectively soak up those internal, high frequency vibrations.

There are plenty more 'nibbles' available if you want LOL. I actually agree with a lot said about accuracy and the looseness in numbers. But some us have striven to get pretty good at those matters and have the backgrounds and know-how. The separation of big and small end weights is the big source of error IMHO, and few understand not just the 'how' to do it well, but also the 'why' of doing it the way it is done.