Balance Shaft Clatter

If you'd like to get rid of the ticking-clacking sound the gear driven balance shaft creates there may, or may not be a solution. I say this because the condition worsens as performance goes up. A stock motor makes the noise but it's less pronounced. A higher compression build makes more sound because the crankshaft speed is more unsteady than it was originally. A two stroke engine's crankshaft turns very different speeds as it goes through the motion of a revolution. You can get an idea of the kind of speeds involved by looking at the piston speed at various RPM. At high rpm the piston is standing still at TDC (though loaded with inertia) but accelerates to somewhere around 50 miles per hour by the time its traveled forty five degrees of crankshaft rotation. Another forty five degrees later it has accelerated to about 70 miles per hour. From right about here it starts to level out then decelerate. At a hundred and thirty five degrees ATDC it's traveling about 40 miles per hour then, it obviously stops completely at BDC. The rest of the rotation makes the piston accelerate similar to the way it did on the first half of the trip though it doesn't ever quite reach the peak speed it did on the way down. Considering this, it's easier to imagine the balance shaft with its small amount of lash which is necessary to keep the parts from sticking can start to chatter. The inertia of the spinning balance shaft wants to make the crankshaft keep spinning a constant rate but the crankshaft has to go through it's speed variations. Every time the crankshaft slows down a little the balance shaft gets ahead of it and produces a click as it takes up the lash. Because of this the balance shaft produces noise several times per revolution. This "model" is more directly related to piston speed than actual crankshaft speed variations but the point comes across well using this as an illustration. To lessen the noise it may be necessary to replace the gears involved - the primary gear is not involved it's the gear under that one which drives the balancer.