If your heat riser is not functioning properly, your crankcase will become contaminated with unburned gas (unless you live where the outside air temperature is 180 degrees). This will lead to premature bearing failure. The heat riser directs instant heat to the underside of the cold intake manifold, warming it up to keep the air/fuel mixture atomized. Without this warming of the intake, the fuel will fall out of suspension and pool up on the bottom of the cool intake runners, then get sucked into the cylinders. Since liquid gas isn't combustible, it leaks past the rings into the crankcase.
