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New Subaru Engine Features Overhead Cam Technology

Sat November 08, 2008 - National Edition
Construction Equipment Guide

Subaru’s EX40 overhead cam engine is now the largest model in its line of high performance air-cooled, four-cycle EX Series engines. Delivering a maximum output of 14-hp (10 kW), the EX40 effectively opens up the EX Series to a new level of applications, including general construction equipment, power generators, compressors and small agricultural machinery.

Utilizing chain-driven overhead cam (OHC) technology, the new engine offers more power, easier starting and quieter operation than competitive engines in its class. OHC technology allows the EX40’s intake and exhaust valves to be positioned to offer lower resistance for the air/fuel mixture flow, thus optimizing engine performance. Designed with a highly efficient pent roof combustion chamber, the EX40 is able to utilize a high compression ratio to produce higher power and torque.

The EX40 meets both CARB and EPA Tier III emission standards, due in part to an OHC valve narrow-angle layout that enables the combustion chamber to function without a special catalyst.

Furthermore, enhanced cooling balance contributes to higher combustion efficiency, thereby lowering fuel consumption.

Easier starts are another advantage of the EX40. An automatic decompression timing system reduces the required recoil pulling force by 30- to 40-percent when compared with overhead valve (OHV) engine designs. In conjunction with the optimized combustion chamber design, starts are fast and easy with no perceptible kickback, according to the manufacturer.

The EX40 is engineered with an inclined cylinder, lighter-weight parts, and improved rotation balance to make it easier to mount onto machinery. Additionally, the new engine’s mount and center height are the same as current EX models to ensure compatibility.

With fewer moving parts, OHC engines produce less mechanical noise than other technologies. The EX40 takes it a step further by utilizing optimized-capacity rigid mufflers and a new resinous air cleaner. Together these features make the EX engines a full 2 dBA quieter in exhaust tone than other same-class engines.

Excessive heat is the primary cause of engine failure. To combat this problem, the EX Series features technology to provide enhanced cooling performance. To utilize every possible cooling area, special heat dissipation fins have been built into the mounting base, cylinder and both the inner and outer crankcase surfaces. Additionally, the OHC technology allows for 360-degree airflow around both the exhaust and intake valve stem areas.

Engine durability is further enhanced by the oil delivery system. A unique oil scraper attached to the connecting rod supplies oil to the cam chain. The cam chain then carries the oil to the overhead cam and valve train. A special rocker cover design and breather system keep the camshaft and rocker arm bathed in oil, yet prevent spouting — whether the engine is level or inclined.

Since arriving on the market in 2001, the Subaru EX Series has sold approximately 1.7 million units worldwide. The four original models — ranging in piston displacement from 126 to 265 cc — have been rated highly by users for achieving both outstanding low-emission environmental performance and user-friendliness, such as low noise and easy start-up operation, while keeping durability and reliability intact.

For more information, call 800/277-6246 or visit

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