A&Q about 350Z
Q:
If an engine is constructed with balance shafts, is there a need for a harmonic balancer? I've been thinking that both components carry out the same function of cancelling crankshaft vibration, thus, wouldn't it be redundant to have both on an engine?
I've read that balance shafts consume some hp, but aren't they more reliable than a harmonic balancer?
I haven't been able to find much info on balance shafts, just a bunch of sites trying to detail removal procedures or sell parts. Could anyone provide me with a link to detailed info on balance shaft operation?
A:
Yes, you want both. The harmonic balancer is used to cancel out torsional vibrations in the crankshaft (twisting back and forth). Unless the engine is externally balanced, it doesn't even balance the rotating assembly. The balance shafts cancel out engine movement due to the harmonics of the engine itself. Be it a rocking or hopping movement. The balance shafts also have no effect on the reciprocating assembly balance. The balance shafts are simply a rotating shaft, so yes, they should be more reliable than the harmonic balancer. You could remove the balance shafts and the engine will run fine (of course if they drive the oil pump or something that's not true). It will vibrate the car more though.
A:
If the torsional vibrations happen to coincide with the natural vibration frequency of the crankshaft (a harmonic), the crank will probably break. Hence the need for a harmonic balancer.