Honda rammer engines, shown here on a BOMAG rammer, have a special oil alert system that only operates during engine starting. This eliminates any nuisance engine stopping from oil splash during operation.
Subaru introduced the ER12, specifically intended for rammer applications, after working closely with OEMs to meet their design specifications.
There is no oil sump on the Wacker Neuson two-stroke rammer engine. Instead, the oil is injected as needed for greater efficiency.
According to Wacker Neuson, two-stroke engines offer the same horsepower at a lighter weight than four strokes, enabling better balance so it's easier to keep the rammer moving.
Wacker Neuson's two-stroke engines have fewer moving parts than four-stroke versions and meet all current EPA emission requirements.
Engine manufacturers agree that rammers are the toughest application for their products. There is no other machine that creates more vibration and takes more abuse from operators than a rammer. Because of that, or perhaps in spite of it, today’s rammer engines have been designed to take their licks.
It started about 15 years ago, when Honda introduced the first four-stroke engine for rammers. It alleviated the need to mix gas and oil, a process fraught with potential for error. Previously, four-stroke engines couldn’t be used on rammers, because laying the machine on its side for transport would cause gas to flood the carburetor, damaging the engine. Since the introduction of Honda’s G100K2 AR, many rammer manufacturers adopted the use of four-stroke technology. Not all followed suit, however.
Wacker Neuson, in fact, still maintains its commitment to the two-stroke rammer, and is the only manufacturer that still builds a two-stroke engine for its machines. “We’ve always manufactured a two-stroke engine for rammers,” says Dave Schulenberg, compaction product manager. “It will always be our core engine for rammers. It’s the only one built specifically for rammers.”
According to Schulenberg, the company’s two-stroke engine is ideal for withstanding the intense vibration inherent in rammer use. There is no oil sump; instead, the oil is injected as needed for greater efficiency. Two-stroke rammers can be laid on their side, he adds.
While it’s true that today’s four-stroke rammers can handle the side orientation, as well, he asserts it’s less reliably true. “As a machine get older, there is still a chance that laying it on its side could cause damage,” Schulenberg explains. “We advise that four-stroke rammers be left in the upright position for a while after use before laying them down.”
He adds that Wacker Neuson two-stroke engines are durable, have fewer moving parts than four-stroke engines and meet all current EPA emissions requirements. The company also manufactures four-stroke rammers, as well as diesel-powered models, to meet customer demand.
“As much as we believe that two-stroke is best, the customer is always right,” says Schulenberg.
Designed for the application
Today, four-stroke engines dominate the rammer market, and leading engine manufacturers continue to work on designing the best engine for the application.
Subaru, for example, introduced the ER12 after working closely with OEMs to meet their design specifications. “The application for which a rammer engine is designed is very unique and specialized, which means the engine and its features have to be matched to each OEM’s product individually,” says Brad Murphy, vice president of sales and marketing, Subaru Industrial Power Products. “So we work very closely with each OEM, essentially customizing the engine to their needs, and virtually every customer receives a different version of the ER12 engine.”
Currently, OEMs can choose between a diaphragm or bowl-type carburetor. “The ER12 also comes with a standard air cleaner. But many times, the OEM will augment our air cleaner with a primary air cleaner, and then our standard unit becomes secondary,” Murphy notes. “Other times, they will design a new, larger air cleaner that’s mounted on the equipment. Either way, we work with them closely on the air cleaner modifications to make sure the engine’s performance isn’t affected, and to ensure the new unit meets emissions standards. Air cleaners and carburetors are both emissions parts, so we need to be very involved with the OEMs to make sure they’re still in compliance.
“A rammer engine is a reciprocating part of the machine,” he continues. “It moves with the product, so items like mass and dimensions are very important and must be integrated into the product design. The weight and balance of the engine and the way it performs are a big deal. It’s completely different than any other engine.”
Honda, for its part, offers two engine models for rammers — the GX100 and the GX120. The GX100 is used primarily for 55- to 65-kg (121 to 143 lb.) rammers, while the GX120 is suited for up to 70-kg (154 lb.) models.
“Honda works very closely with our OEM customers to match our engines to their applications and their specific requirements,” says Rick Wendt, national manager, OEM sales, Honda Engines. “For example, some OEMs use their own air intake system and we were able to match our components with theirs to ensure that all emissions regulations were satisfied. In addition, we always confirm the connection points between our engine and the OEM frame components so the combined product will be best for our mutual customers.”
Features and benefits
Honda’s rammer engines have two types of carburetors (diaphragm and float), which both incorporate a special structure to prevent overflow when the rammer is laid down. “In addition, our GX100 split-case OHC design allows the engine to be mounted directly to the rammer with no need for an engine base support,” Wendt says. “This allows for a compact design with improved strength and toughness against high vibration.”
Rammer engines are subjected to high vibration and operation in dusty environments. “[Honda rammer engines] have designed-in protection against carburetor overflow and a special oil alert system that only operates during engine starting to eliminate any nuisance engine stopping from oil splash during operation,” Wendt says. “Our designs offer industry leading protection against high-vibration operation in dirty/dusty conditions.”
According to Murphy, the No. 1 advantage the Subaru ER12 offers is that it’s a completely original design specifically and exclusively intended for use with rammers. “We didn’t copy a design or attempt to re-purpose an existing engine for a rammer,” he says. “It’s compact and lightweight, and maintains an excellent center of gravity to effectively transmit power to the ground, which in turn allows the rammer to offer superior performance.”
Murphy adds that the ER12 offers quite a few unique features that contribute to the optimally balanced, lightweight design, while allowing it to provide more power per cc of displacement. “The starting point is the overhead cam (OHC) design. That’s really what allows the engine to offer improved performance and more power output,” he comments.
Further enhancing the design, the crankcase features a thin wall yet durable construction and a lightweight aluminum flywheel. Subaru has also reduced the muffler size and weight.
“Also, the engine has a unique torsion bolt structure. High-strength torsion bolts extend from both the cylinder head and the gear cover deep into the crankcase,” Murphy says. “This unique design allows less material to be required on the cylinder, heads and blocks, further reducing overall weight while improving structural strength.”
The torsion bolt structure contributes to optimal balance, which is key in rammer engineering. The ER12 is designed to be balanced very close to the mounting face and on the side-to-side axis for best compaction performance and easy operation. The recoil has been integrated into the flywheel and blower housing, further enhancing balance and overall engine performance.
“Two other major features... are the pressure lubrication system and low oil pressure shut-off system. Because of their constant up-and-down motion, rammer engines are difficult to lubricate, so the ER12 was designed with a pressure lubrication system,” Murphy points out. “A gear pump transfers oil from the bottom of the crankcase to various parts of the engine that need critical lubrication. The low oil pressure shut-off system does exactly that — shuts off the engine if the oil level gets too low. It also allows the rammer to be tipped on its side without any problems, which is great for transportation of the entire unit.”
A tall order
Rammer engineering is tricky, and balance and weight are the two toughest challenges.
“Normally, you design an engine to handle the internal force of the engine, and it is stable on the product,” Murphy notes. “But in the case of a rammer, it needs not only the strength to handle the internal forces, but it also has to be able to handle the rigors of being bounced up and down and the G-forces being applied because of the product.
“As you can imagine, maintaining strength while keeping the engine light and compact is difficult to do, but it’s essential on this product,” he continues. “The challenges presented by rammer engineering just further drive home the importance of having an engine specifically designed for this application.”
Peter Witt, Weber MT, maker of rammers and plate compactors, points out that the power to weight ratio has always been vital to the design of a rammer engine. “Unlike with vibratory plates, creating a weight that can be handled by one person (120 lbs.) is critical. Older designs may meet the weight criteria but the engine was too weak. One could stand on the rammer shoe and literally stop the percussion function (not Weber but some competing brands),” Witt says.
Honda engines are designed for durability and “startability,” as well as simple operation and service. “The unique oil alert system allows the user to check the oil only before starting instead of more frequently, which minimizes the opportunity for dust to enter the crankcase,” Wendt says. “The OHC belt design in the GX100 is quiet and has very high durability, designed to last the life of the engine. The split-case design allows for easier service due to no lower engine support required. All of our controls are clearly labeled and make the Honda engine simple to use.”
He adds, “Honda’s engine application process helps to ensure that specific durability requirements and tests are met or exceeded (drop test, laydown condition, operator access to controls, etc.).”
While engine suppliers have worked hard to advance the state of the art of four-stroke rammer engines, Schulenberg maintains his position that two-stroke rammer engines are unsurpassed, adding that the incorporation of Wacker Neuson’s compensating carburetor has significantly increased the machines’ environmental friendliness. “Since making improvements to our rammers in 2010, our two strokes have the lowest total emissions of any other rammer on the market,” he states.
“Two strokes are much smaller than four-stroke engines, but offer the same horsepower. They offer better balance because they’re lighter, so it’s easier to keep the rammer moving. This results in less operator fatigue and increased productivity,” he indicates. “Customers are worried about uptime, so the easier you can make a rammer to use, the better.”