Thread: VERY small SBC Harmonic balancer/pulley troubles

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Well, I can get the aftermarket (Dorman) brand for 37 bucks, and I'm sure I can drill and balance a piece of aluminum to fit inside... and that sound like the cheapest, most cost-effective way out...Although i don't see anything wrong with the one I pulled off, it was wiggling, even with the center bolt in the crank snout impact-gunned on.. so I guess it's warped itself, or the rubber has started to come loose.. I've seen what happens when one of those things lets go, and it wasn't pretty...aluminum radiator, plastic timing chain cover, water pump, and probably the crank snout, but I didn't stick around long enough to fully assess the carnage...

Not to get too far afield, the correct term for this component on all stock Chevy small blocks (with the exception of the SB 400) is “harmonic damper” or to be perfectly correct, “crankshaft harmonic damper”. The term often used is harmonic balancer, which suggests the unit “balances” the engine. Except as noted above (SB 400) this statement is misleading as the crankshaft assembly is internally balanced. A harmonic dampers purpose is to address torsional vibration.

Torsional vibration occurs in the crankshaft of all internal combustion engines. This is a result of an immediate and drastic reversal of load on the piston, wrist pin, connecting rod and crankshaft during compression, followed by the ignition of the compressed fuel and air in the combustion chamber. Subsequent relaxation of the load following combustion causes deflection or flexing of the crankshaft (up to 2 degrees). The crankshaft literally “snaps” back in the opposite direction! This sets up an oscillating vibration which continues until dissipated by internal friction or damping. It is possible for these oscillations to come into phase with each other and create potentially damaging torsional “peaks” in the crankshaft. Unless the magnitude of these torsional “waves” is controlled, damage most certainly will occur to engine components, specifically; wear of the timing chain and gears, pitting or cupping of the camshaft and lifters, broken valve springs and, scuffing of your crankshaft bearings. In extreme cases, left unchecked, torsional vibrations can cause loosening of bolts (flex plate or flywheel) or even a broken crankshaft. The damper is not a balancer. Its job is to control torsional vibrations on internally balanced (neutral) engines. And yes, as stated above, it provides a mounting surface for pulleys.

So – when you hear someone call it a "balancer", you can politely remind them that it's a harmonic damper, not a "balancer". They’ll probably look and you and say, “yeah sure – whatever.” But you will know that you’re correct!

Whew - that felt good.

Regards All,
Glenn