Abstract: Disclosed is a lubricating system for lubricating moving parts in a crank case of a four-stroke-cycle engine. The lubricating system comprises an oil tank for holding oil, an oil passage connected to the oil tank and an engine crank chamber, an oil supply means for supplying fine particles of oil held in the oil tank to the moving parts in the crank chamber via the oil passage, and an oil removing means for removing the fine particles of oil applied to the moving parts in the crank chamber, from the crank chamber without forming oil accumulation. To supply the fine particles of oil to the moving parts in the crank chamber, the oil of a liquid form is thrown to impinge against the moving parts in the crank chamber or is mixed with a gas entering the crank chamber.

Abstract: Air is drawn into the crank chamber when the negative pressure is built up in the crank chamber, and the air mixed with the blowby drawn into the crank chamber is led as the secondary air to the exhaust gas discharge section when the positive pressure is built up in the crank chamber. Thus the secondary air is mixed with the exhaust gases discharged from the combustion chamber, and the mixture of the exhaust gases and the secondary air is burned again (oxidized) in the exhaust gas cleaning section, thereby cleaning up the exhaust gases. Furthermore, the present invention is provided with two valves for checking the back flow of the air while maintaining the air flow from the crank chamber to the exhaust gas discharge section. One valve (first valve) is disposed within the intake passage and opens when the negative pressure is built up in the crank chamber. The other valve (second valve) is disposed within the guide passage and opens when the positive pressure is built up in the crank chamber.