Small gas engines

Ah, the good old days, when everybody smoked unfiltered cigarettes and your portable power equipment ran off noisy, fume-spewing, two-stroke engines – and nobody cared.

“In the past we didn’t have to worry about emissions,” says Dale Gabrielse, training manager for Robin America. “They ran them as rich as they wanted. More gas equaled more power.”
Today, you can still find some two-stroke gas engines with vastly improved emissions, but most are on consumer grades of equipment. For contractor grades of equipment – such as powered concrete trowels, screeds, vibrators, generators, pumps and welders – the four-stroke engine is becoming the engine of choice.

Driving this trend are emissions regulations set forth by the EPA. As with big diesel engines, those emissions standards will only get tougher in the future.

Two-cycle engines, however rowdy and inefficient they may have been, were certainly popular in their day. They were simple, uncomplicated and had a great power-to-weight ratio, especially for the smaller equipment like concrete saws, string trimmers, and vibrators. But the rapid migration toward four-cycle engines in the past six years has brought virtually no trade offs and only a few complications. Four-cycle engines burn cleaner, use less fuel, and are quieter and lighter. They also start much easier, especially in cold weather. And prices have stayed in line with the two-cycle engines they’ve replaced. Most recently the introduction of mini four-stroke engines (under 50cc) has brought this technology down to the smallest equipment applications.

Down but not completely out
One of the holdouts for the two-stroke design has been the rammer market. “It’s a smaller, lighter engine; and it’s simpler, not a lot of parts,” says Marc Leupi, a product manager for Wacker. “And in an intense application like a rammer, you get a lot of vibration and impact that four-cycle engine makers have struggled with. It took a lot of time to get it right.”

To survive this intense pounding, engine manufacturers had to develop four-cycle engines that were geared specifically for the rammer/tamper market, rather than use a generic engine, says Peter Price, product manager and trainer for Bomag’s light equipment division. “What you’re seeing now is an engine that will withstand the abuse two-cycle engines experience.”

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The other issue with tampers was that the two-cycle engines, being self-lubricating, could be worked, transported or stored in any position. Four-cycle engines with float bowl carburetors and oil sumps couldn’t be positioned too far off vertical without risking oil or fuel spilling into the filters. “About six years ago we worked with Honda to develop a four-cycle engine for a tamper that would allow it to lay on its side, and that became a big advantage,” says Price.

“In the past, the advantage the two-stroke engines had was that they had the higher impact force, but with the new four cycles, they’ve overcome all those objections and I’ve seen the advantage of two-cycle engines dwindling drastically,” Price says. “We’ve discontinued our two cycles as of this year.”

Robin still manufactures two-cycle engines – although fewer models than before – primarily for rammers and tampers, but it has also developed a line of mini four-stroke engines
for this demanding application.

Customer preferences
Chuck Mayo, general manager at Vibrastrike, sees customer interest in four strokes picking up, especially with the multi-position capabilities. “We’ve offered the Honda four stroke for a number of years and starting last year we began offering the Fuji-Robin four stroke. It’s not that big of an issue, except for our concrete vibrators,” he says. “With a power screed the engine pretty much stays in a vertical plane.”

One maintenance chore the two strokes require that the four strokes don’t is pre-mixing your gas and oil. Manufacturers tout that as a benefit, but opinions are mixed. “It’s a tradeoff,” Mayo says. “You can still burn a four-stroke engine up if you run it without oil.” Gabrielse says pre-mixing never was a big issue with contractors since they pre-mixed big batches of fuel ahead of time. For their four-cycle engines, contractors have to check their oil levels daily, so for most commercial users it’s a wash, he says.

The EPA standards cometh
Honda, never much into two-cycle engines to begin with, started developing an industrial/construction grade of four-cycle engines (its GX series) as far back as the early 1980s. “Efficiency in emissions and fuel economy are tough to promote in this kind of business,” says Joel Borowski, Honda’s manager of technical operations. “But now that we have CARB (California Air Resources Board) and EPA standards, everyone has gotten into the overhead valve design. They have since done a lot of work on the side valve designs to make them cleaner, but for the commercial market everybody has gone to overhead valves because of durability and clean, efficient operation.”

“The overhead valve design changes the position of the intake and exhaust valves relative to the combustion chamber,” says Paul Blum, marketing product manager for Kohler single cylinder engines. “It’s a much more efficient, clean burn. You get much less carbon monoxide, hydrocarbons and nitrogen oxide out the tailpipe. It’s the same basic technology they’ve used in automotive engines for years.”

Emissions and the EPA aside, the other big push in small engine technology is to try to make them more productive for end users. This includes changes such as better filters that don’t have to be replaced as often, longer oil change intervals, increased fuel tank capacity and greater fuel economy, Blum says.

Quiet, please
Noise, while not a big issue in the United States, is an important criteria for engine certification in Europe, but most manufacturers see those standards coming to the United States in a few years anyway. “One of the biggest challenges we have as equipment manufacturers is reducing the decibels of the overall machine,” says Bomag’s Price. “There have been great strides taken by the engine manufacturers to help us reduce noise by using different materials and composite materials.”

Reducing noise also means working closely with the OEMs that put the engines in their equipment, says Blum. On a lot of equipment used in the concrete trades the engine noise becomes secondary once you engage the machine, he says. So the most effective noise reduction is achieved by designing the engine as a total package solution for the OEMs. The same holds true for designing engines for reduced vibration and better cooling, Blum says.

Regulations aside, reduced noise levels may give contractors a competitive edge by enabling them to work at night, around schools, in crowded environments, indoors or anywhere noise levels will be of a concern to project owners.

Looming on the horizon are Tier 3 California standards coming due in 2007 for gasoline engines under 225cc. According to Cam Litt, Kohler’s marketing product manager for twin-cylinder engines, these will likely require the addition of a catalytic converter to control exhaust emissions, but the standards will also regulate evaporative emissions – trace amounts of gas that escape from the fuel tank, fuel cap and fuel lines. These regulations won’t affect engine design immediately, Litt says, but are affecting the engines on the drawing board.