The Stovebolt Site Forums The Shop Area Engine Shop Harmonic Dampener-235's

OK, please educate me. There have been several recent posts about the harmonic or vibration dampener.

Beside providing the timing mark, what is the purpose of the dampener? Is it just a smaller flywheel at the front? Why is it make out of 2 pieces seperated by rubber?

The harmonic damper ,or balancer as it is also called, aids in the removal of unwanted vibrations produced by the spinning crankshaft, flywheel, the pistons, rods, and camshaft. Preferably all these parts should be balanced by a machine shop during a complete engine rebuild. The "rubber" that is sandwiched between the two rings of steel absorbs the vibrations. These can go bad over the years and can separate from age, as I found out on a small block Chevy V8 and also my friend had one come apart on his '48 Chevy 216 motor. The balancer on the 235 does not have the timing mark. The timing mark is located on the flywheel and is viewed thru a hole in the bell housing on the distributor side of the engine. The V8 motors have the timing mark on the harmonic balancer.

The harmonic balancer is also called a "vibration damper". It sets up an opposing force to the twisting motion the connecting rods induce into the crankshaft as the cylinders fire by absorbing some of the energy in the rubber damper, and then snapping the outer ring back at a different frequency than the input from the rods. It's supposed to prevent vibrations and possible crankshaft breakage due to harmonics in the crankshaft. Some engines such as the Chevy small block 400 also use an out-of-balance flywheel and dampener to help balance the crankshaft since there's not enough room inside the crankcase for big enough counterweights on the crank.
Jerry

I have seen an article from the early days of engine development where they had graphs of the vibrations across a number of frequencies with and without the damper. The differences were quite impressive.

Loads of folks here will know better than me, but I feel I should contribute when I can, so here goes . . .

The crankshaft suffers through loads of force in the process of torque-creation. All the controlled explosions in the cylinders translate their force to the crank. As the crank turns, the engine wants to turn the opposite of the crank. And the off-set combustion in the cylinders puts different twisting force on different parts of the crank at different times.

The vibration dampener acts like the shock absorber on a tennis racquet. The rubber in the dampner helps absorb and redistribute the shocks of the crankshaft forces, providing for smoother turning action. The other name for the dampner, the Harmonic Balancer, I think refers to the vibrations set up from all these forces, which are measured in sine-waves, much like music can be. I guess it keeps the competing forces "in harmony", by "balancing" them out.

OK . . . I think I may have made that more complicated than it needed to be . . . Must me readin' too many books.

PS: I didn't think our trucks HAD timing marks on the dampner, only on the flywheel - I don't recall my dampner being indexed at all to the crank shaft?
-Michael

What they said! On my 235, the damper has a rattle from the rivet being loose, and it sound terrible when I'm in front of truck. On my soon to be installed 261, the P/O installed a one groove late model 194/250 style damper. I'm kinda glad to have it, 'cause I can bolt an extra pulley to it ( for power steering) later.

As always the Stovebolt guys have come through with great info. You all helped to put into perspective. When I wrote about timing marks on the VD I was picturing my 62 Corvette 327 because I had just timed that. I have not worked on the 235 but do recall seeing the timing hole in the bell housing. Thanks for infoming me of that!

Happy Thanksgiving to all and say a special prayer for all our Service People away from their families.

Regards,

Bob