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United States 

Environmental Protection 

Agency 

Air and Radiation EPA420-F-00-008 

March 2000 

Office of Transportation and Air Quality 

Regulatory 

Announcement 

Minor Amendments to Emission 

Requirements Applicable to Small 

Nonroad Spark-Ignition Engines and 

Marine Spark-Ignition Engines 

The U.S. Environmental Protection Agency (EPA) is adopting several 

minor revisions to current regulations concerning exhaust emissions 

from: (1) nonroad spark-ignition engines at or below 25 hp, such as 

lawnmowers, string trimmers and chainsaws (known as the “Small SI” 

rule); and (2) marine outboard and personal watercraft spark-ignition 

engines used in recreational boats and jet skis (known as the “Marine 

SI” rule). These revisions address minor issues that have arisen since 

EPA began implementing these two rules in 1997-1998. 

Background 

The amendments being adopted address four specific issues for Small SI 

engines and Marine SI engines. 

•	 The amendments specifically classify model airplane engines as 

“recreational” and thereby exempt them from coverage under the 

Small SI rule. 

•	 The amendments revise the definition of “handheld” in the Small SI 

rule to include engines that may weigh too much to be “handheld” 

under the current definition only because they have advanced or 

additional emission control technology. 

Printed on Recycled Paper 
Model airplane 

engines 

The weight 

limit in the 

definition of 

“handheld” in 

the Small SI 

rule 

•	 The amendments provide compliance flexibility to small volume 

Marine SI engine manufacturers who may face difficulties with the 

existing averaging program because they have very limited product 

lines. 

•	 The amendments limit the applicability of the current replacement 

engine provisions in the Small SI and Marine SI rules so that the 

replacement engine provisions cannot be misused by importers who 

may be “manufacturers” by definition of the Clean Air Act, but do 

not actually manufacture engines. 

How does the rule address each of these issues? 

Background: When the Small SI rule was written, EPA was unaware that approximately 8,000 nonroad spark ignition engines are 

sold in the United States each year that are used by hobbyists in 

model aircraft, boats and cars. EPA has no emission data on these 

engines and is concerned that the Small SI test procedure may not 

be appropriate to represent the operation of these engines. Further, 

many of these engines are produced by very small entities that may 

lack the resources to conduct emission testing and certification. 

These engines represent a just a fraction of a percent of the 

20,000,000 Small SI engines sold each year in the United States 

that are covered under the Small SI rule. 

Final rule: There is a minor change to the definition of the term 

“recreational” as used in the Small SI rule so that it would include 

model airplane engines. We believe that the existing definition and 

regulatory text already place engines used in model boats and cars 

under the term “recreational.” “Recreational” engines are excluded 

from coverage under the Small SI rule. We plan to evaluate the 

emissions and appropriate standards and test procedures for recreational engines in a future rulemaking. We believe this is a more 

appropriate forum to determine whether regulations are necessary 

and appropriate for model airplane, car and boat engines. 

Background: Handheld equipment has historically used lightweight 

two stroke engines which have much higher emissions than the 

heavier four stroke engines. While the Small SI rule regulates the 

emissions from both “handheld” and “nonhandheld” engines, it 

applies less stringent standards to “handheld” engines than to 

“nonhandheld” engines. To limit the use of two stroke engines to 

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Compliance 

flexibility for 

small volume 

marine SI 

manufacturers 

equipment that truly must be “handheld,” the Small SI rule provides 

for equipment weight limits above which a piece of equipment is 

considered non-handheld and must use an engine which meets the 

more stringent nonhandheld engine standards. 

Recently, a manufacturer of handheld equipment pointed out that 

the current weight limits on handheld equipment prevent the use of 

lightweight four stroke engines that are intended for handheld 

equipment and are much cleaner than conventional two stroke 

engines. 

Final Rule: We are not changing the weight limits, but in cases 

where a piece of equipment exceeds the weight limit, the engine 

will still be eligible for the handheld standards, if the excess weight 

is directly attributable to the use of a four stroke engine or other 

clean technology. 

Background: The current marine SI standards are centered around 

an averaging, banking and trading program whereby engine manufacturers can offset engines that exceed the emission standard with 

engines that are under the standard. Such averaging schemes are 

common in EPA rules and allow EPA to impose tighter overall 

standards than might otherwise be possible in a situation where 

every engine had to comply with the same standard. 

While averaging, banking and trading (ABT) programs have many 

advantages, they may pose difficulties for very small engine manufacturers that lack a diverse product line. These companies may 

only have one engine family and, if it exceeds standards, they will 

not have a “clean” engine family to offset it. Theoretically, these 

companies could buy emission credits from other marine SI engine 

manufacturers, but there is no guarantee that credits will be available for sale at a reasonable price. EPA’s experience with ABT 

under other rules indicates that manufacturers are reluctant to sell 

credits to competitors. 

We have become aware that some very small manufacturers of 

marine SI engines exist who may be unable to offset the emissions 

of their sole engine family in the later years of the marine SI standard phase-in. These manufacturers either require additional time to 

comply or to stage an orderly exit from the market. These manufacturers point out that their products may be cleaner than similar size 

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Applicability 

of the 

replacement 

engine 

provisions to 

certain 

importers 

engines from larger competitors, but they will lack the emission 

credits to cover them that their larger competitors will generate 

from other engines. 

In more recent nonroad rules, we provided special flexibilities for 

small volume manufacturers. Typically, these flexibilities would 

exempt small volume manufacturers from phase-in requirements 

and require them to simply comply with the final phase-in requirement. 

Final Rule: Because the marine rule has an unusually long (9 year) 

phase-in, we are not exempting very small marine SI manufacturers 

from the entire phase-in, but rather a manufacturer producing less 

than 1000 engines per year would be allowed one four-year “window” beginning in model year 2000 or later when it could maintain 

a negative credit balance, subject to some very specific constraints. 

Background: Our replacement engine provisions permit engine 

manufacturers to sell uncertified pre-regulatory engines or certified 

engines built to earlier standards in cases where an owner requires a 

replacement engine, and no certified engine is available (either 

performance or physically) to fit the equipment. Typically, the 

manufacturer must ascertain that no certified engine from any 

manufacturers’ product line is available that will fit the equipment. 

The engine manufacturer must also take the old engine in exchange 

for the new uncertified engine and destroy it. 

These replacement engine provisions affect only a very small 

fraction of engines sold each year and serve to aid equipment 

operators who experience premature engine failures where engine 

repair or rebuild is not available, costs too much, or takes too long. 

Under the Clean Air Act definitions, any importer of an uncertified 

engine is considered a “manufacturer.” Such importers may actually 

have had nothing to do with the actual production of the engine. 

Abuse could occur under the Marine SI and Small SI rules if, for 

example, an equipment operator imported an uncertified engine. 

Since it would be a “manufacturer” by definition, the equipment 

operator could determine that no certified engine was available from 

itself, and improperly import an uncertified engine, when a certified 

engine might actually be available from the original engine manufacturer. 

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Final Rule: We are amending both the Small SI and Marine SI 

replacement engine provisions to require that, if an uncertified 

replacement engine is to be imported, the engine manufacturer’s 

designated representative must determine that no certified engine is 

available to fit the equipment. 

How will these revisions affect the Small SI Phase 2 

Rule? 

These revisions affect the existing Small SI engine rules. The Phase 1 

rule took effect in 1997; the Phase 2 nonhandheld rule was adopted in 

March 1999; and the Phase 2 handheld rule is being adopted along with 

these amendments. 

How can I get more information? 

You can access the entire text of the final rule, including both the preamble and the regulatory text, electronically on the Office of Transportation and Air Quality Web site at: 

http://www.epa.gov/otaq/nonroad.htm 

When you access this web site, click on the “Nonroad Engines and 

Vehicles” icon. Then click on “Laws and Regulations,” then “SparkIgnition Engines” and then scroll down to “Spark Ignition Engine Emissions Regulations/Related Documents.” 

For further information on this final rule, please contact John Guy at: 

U.S. Environmental Protection Agency
 

Office of Transportation and Air Quality
 

Certification and Compliance Division (6403-J)
 

401 M Street SW Washington, DC 20460
 

Email: guy.john@epa.gov 

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How can I view comments sent to EPA on this final 

rule? 

Materials relevant to these amendments are contained in Docket No. A98-16 and are available for public inspection and copying at the following address: 

U.S. Environmental Protection Agency
 

Air and Radiation Docket (6102)
 

401 M Street SW
 

Washington, DC 20460
 

The docket is located in Room M-1500, Waterside Mall (ground floor) 

and may be inspected from 8:30 a.m. to noon, and from 1 to 3 p.m., 

Monday through Friday. Copies of information in the docket may be 

obtained by request from the Air Docket by calling (202) 260-7548. A 

reasonable fee may be charged for copying docket materials. 

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