Four-Cycle Tamper Mates Convenience with Power

By Walt Moore | September 28, 2010

Bomag BT65/4
This new Bomag BT65/4 tamper is powered by a 3.3-hp, four-stroke Honda GX100 engine that can be transported in a horizontal position without concern for oil-contamination of the cylinder, muffler, carburetor or air filter.

The two-stroke-cycle (two-stroke) engine has long powered tampers and continues to do so. The two-stoke, because it does not depend on an oil sump for lubrication, can be operated at extreme angles and can be thrown into the back of a pickup truck without concern that oil in the sump will leak into the cylinder, air filter, muffler or carburetor. Plus, the engine is lightweight, simple in design, durable and usually economical to repair. So why would a tamper manufacturer like Bomag spend three years developing a tamper with a four-stroke-cycle (four-cycle) engine?

Because, says Peter Price, product manager for Bomag Light Equipment, the four-cycle engine can be made to more easily comply with future emissions standards. Plus, the four-cycle produces fewer exhaust fumes and it's less noisy, both big advantages when used in the confinement of a trench, and you don't have to mix oil with the fuel. But, on the down side, says Price, the four-cycle's oil sump can leak into sensitive areas of the engine if the tamper is not in an upright attitude; the four-cycle is heavier, affecting tamper balance; and its more sophisticated design makes it vulnerable to the pounding forces the tamper produces.

Early attempts at using a four-cycle engine on a tamper, says Price, were not completely successful, and often resulted in "de-tuning" tamper performance to reduce impact force in the interest of prolonging engine life. And although some of these early engines had a side oil reservoir that allowed laying the tamper on one side, it could not be placed in any other horizontal attitude without possible oil leakage occurring.

Complete redesign

When Construction Equipment visited with Price at Compaction America in Kewanee, Ill., he explained how Bomag's new four-cycle-engine tampers have been designed to overcome these drawbacks. The new engine, developed in partnership with Honda, has features such as a diagonally split, rigid crankcase and a one-piece cylinder that address the issue of oil infiltration into other components, effectively eliminating the problems resulting from angled operation and horizontal storage. Plus, he says, engine components have a robust design that enhances durability.

But creating a four-cycle tamper is not as easy as bolting on a new engine, even one as well designed as the new Honda, says Price. The issues of tamper balance, weight distribution, travel speed and performance had to be completely reevaluated with the new engine, resulting in essentially redesigning the tamper from the shoe up. In fact, says Price, Bomag field-tested 72 different shoe designs to find the one that best complemented the overall performance of the four-cycle tool. At the same time, however, the redesign process was careful to retain features that customers have come to appreciate, he says, such as its air-cleaning system and impulse-style carburetor.

In Bomag's assessment, its new tamper combines the operating convenience of a four-cycle engine with the high stroke and impact force of a two-stroke.

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