Engine Repowers: The complicated business of putting a new diesel in an old machine

Updated Jul 16, 2017
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Maintenance Lead 0717 E1499788703511
It used to be easy to replace an engine in an older piece of diesel-powered equipment in the era before emissions controls.

In many cases today, that process doesn’t start with an engine hoist, but instead requires permission from air quality regulators before you touch a wrench. That’s because with each new iteration of diesel exhaust emission technology – from Tier 0 to Tier 4 Final – engines produce fewer emissions and the government doesn’t want any backsliders. You can’t put an older tier engine in a machine that came from the factory with a newer, cleaner engine. It’s the law.

The good news is that in most of the country you can still do a like-for-like swap, putting a Tier 3 engine in a machine that had a Tier 3 engine in it previously and on down and up the line. And in many cases, you can upgrade from a Tier 1 to a Tier 3 engine, or Tier 2 to Tier 3 and thereby reap the benefits of a better, more efficient engine.


But in California and many large cities with air pollution problems, even a like-for-like swap may not satisfy the authorities.

The California Air Regulatory Board doesn’t so much look at individual machines as it does a contractor’s total fleet emissions output. “The CARB rules have a lot of particulars you want to stay abreast of,” says Darin Schultz, sales manager at Perkins Pacific. “We tell customers to use a consultant to find out exactly what they can and can’t use.”

Maintenance0717 AIf a California contractor has a mostly new fleet of equipment powered by Tier 4 Interim or Tier 4 Final engines, CARB may decide this contractor can do the occasional like-for-like swap on a few of his machines powered by a lower tier engine. If a contractor has a lot of mostly older machines, however, CARB may decide the contractor needs to put in a higher tier engine in an older piece of equipment, or scrap the old equipment and buy a new machine to reduce his total emissions output.

“California has a plethora of regulations – from off-road, on-road, portable, stationary and ag –  that drive the users to make hard decisions whether to replace or rebuild,” says Glen Chrusciel, program manager, retrofit and repower at John Deere Power Systems. “Initially it was a lot of rebuilds, taking Tier 1 machines and upgrading them to Tier 3. That was easy. Now as we’re getting close to 2020, a lot of these milestones become difficult to meet. We’re finding replacement of the whole machine to be the best bang for the buck.”

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The goal of CARB and the EPA, says Schultz, is to reduce the number of lower tier engines over time. In fact, engine vendors are required to destroy the older tier blocks they remove, by putting holes in them, taking a photo of the destroyed block and sending that and the serial number to the EPA.

Keep in mind that it’s not just California that restricts what you can do with a repower. So check with your state or local air quality officials before making a decision, buying an older piece of equipment or starting on any course of action.

Technical challenges

Putting a Tier 3 engine in older equipment designed for Tier 1 or Tier 2 engines isn’t difficult. The designs of those engines changed little from tier to tier. And doing so in California may earn your fleet some emissions credits. But it is difficult to put a Tier 4 Interim or Tier 4 Final engine in most machines powered by Tier 3 or earlier engines.

“When we first started, we had a lot of Tier 1 and Tier 2 engines out there,” says Terry Oftedal, program manager, engine application, construction and forestry division, John Deere Power Systems. “Depending on the vehicle platform, we could usually upgrade with minimum effort. But now that we’re into the Tier 4 Interim and Tier 4 Final, the aftertreatment really changes the architecture of the vehicle as well as the electronic integration.”

Tier 4 Interim engines make substantial use of diesel particulate filters or DPFs. These large canisters take the place of the muffler, and filter out particulate matter from the exhaust. DPFs are so large that equipment manufacturers generally had to redesign their machines to get the DPFs and related plumbing to fit under the sheet metal.

Most smaller Tier 4 Interim and Tier 4 Final engines (under 75 horsepower) have been able to avoid using a DPF, but they all contain a similar, if somewhat smaller, component, the diesel oxidation catalyst (DOC), which does much the same thing and likewise tends to enlarge the footprint of the engine.

Tier 4 Final engines added an additional layer of emissions technology, the selective catalytic reduction system, or SCR. In an SCR system, the exhaust stream is injected with a mist of diesel exhaust fluid (DEF) and water and then run through a catalyst. This transforms the nitrogen oxides (a harmful pollutant) in the exhaust into harmless water and nitrogen but requires storage tanks for the DEF, dosing hardware and related plumbing.

“From a practical standpoint, the primary problem is simply having enough space to accommodate the Tier 4 replacement engine,” says Mike Rochford, director of emissions regulations and conformance at Caterpillar. “When considering a repower to Tier 4 in an older machine, there must be room to fit the SCR aftertreatment, a DEF tank, controls and a cooling system that can be up to 30 percent larger than the previous engine. While some machines have the space to fit this Tier 4-related equipment, often the engine compartment does not have the extra room.”

Another complication with the new engines is the sophisticated electronic controls and sensors that help them and the machines they power be more efficient, says Oftedal. Higher tier machines all use an electronic control module (ECM) that acts as the machine’s brain. The ECM gets information from sensors in the transmission, details about engine speeds, temperatures and loads, data about the exhaust aftertreatment and how well it’s performing. Algorithms in the ECM then decide on power levels, injection timing, shift points and a wide range of performance options to maximize the machine’s productivity and fuel efficiency. To put one of these engines in an older tier machine may require an almost impossible amount of reengineering and additional upgraded componentry to communicate with the ECM.

“It’s a whole new world of software integration that is not backwards compatible,” says Oftedal. In these cases, you’re going to be better off just buying a new machine.

You can sometimes successfully repower from a Tier 3 or earlier engine to a Tier 4 Interim or Tier 4 Final engine with applications in which the engine is static and not bolted into a mobile piece of equipment, says Carl Micu, manager of OEM engine sales Americas and drivetrain sales worldwide, John Deere Power Systems. Examples include large trash pumps, light towers and gen sets. In these applications, the engine is often mounted on a skid or platform, and you don’t have the space constraints that occur with mounting an engine in a piece of mobile equipment. And since the engines in these applications generally run at a steady rpm and don’t have to rev up or down in response to loads, they don’t need sophisticated software running the ECM.

Getting it done

Assuming you can meet all your emissions requirements, it’s best to consult the engine OEM and discuss the cost and feasibility before you decide to buy used equipment that needs a new engine or to repower something in your own fleet.

“Is it in suitable condition to justify the investment?” asks Rochford. “Items such as the machine frame condition, age and intended working conditions factor into the assessment. The condition of the hydraulics and drivetrain is the next biggest driver as to whether a machine would make a good candidate.” Owners must also analyze the cost relative to other options, including the price of a new machine, used machine or rental/lease options, Rochfort says.

And note that your engine provider will likely need to assess the machine you’re putting it in unless it’s a swap for an identical engine model. “You have to do an application and appraisal,” says Schultz. “Make sure the cooling system will cool, the charge air system will operate properly. It’s an overall appraisal of the application to the engine. If the customer wants to use his own radiator package or other components then we have to sign off on those. A lot more testing may be involved.”

Engine distributors typically have kits available to hook up the most common engine repowers, and for these, the appraisals and engineering have already been done. But if the repower you’re considering is something they’ve not yet encountered, the extra engineering and testing required to ensure that it works may add to your cost.

Bigger is better

As a general rule, bigger machines are better candidates for repowers than compact units, says Chrusciel. “When you get to the point where you need to replace the engine on a compact machine, that machine is usually wrung out. We find many times it’s just better to go out and get a new machine.”

“Scrapers have been popular for repowers, as they have large engine bays, generate large numbers of hours per year and are durable platforms,” says Rochford. “The same applies for motor graders, off-highway trucks, track-type tractors and wheel loaders.” On these big frame machines, the repower cost is normally less than 15 percent of the cost of a new replacement machine, he says.

The decision to repower or not should also take into consideration your fleet’s profile and needs. “Go back and do an inventory of your machines and look at the work you’re going to be doing over the next 10 years or so,” says Micu. “Once you do that, you can get a pretty good idea of what machines are going to be around in that time and what you’re going to need to replace. And then you’re going to have to make some tough decisions based on that.”

Funding available

If you want to put a Tier 3 engine in a lower tier piece of equipment or you want to retrofit equipment with more efficient exhaust aftertreatment devices, the government has money available to help you. There are two main federal programs for diesel-powered construction equipment:

There are also numerous state and municipal programs to help fund diesel repowers and retrofits. For a full list, check out the Diesel Technology Forum.