ATV Engine Rebuild Kits Buying Guide

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ATV Engine Rebuild Kits Buying Guide

Anyone who has an ATV knows that riding it is just part of the game. If an owner is going to use it, especially on rough terrain, he or she is going to have to maintain it, too. Unlike repairing a car, they are much easier to work on, and if the job does not get finished today, there is always tomorrow.

Repairing and rebuilding an ATV engine is great training as well, for learning how to rebuild an engine. Although the ATV engine is smaller, it is essentially the same as a full-sized vehicle engine. Being smaller than a car engine makes it easier to work on, even though all of the same work needs to be done.

Besides having the right information and the right tools, the other item that is needed before starting to rebuild an engine is a rebuild kit. There are different levels of kits, but at the most basic level, a rebuild kit consists of all of the gaskets and seals needed for a particular engine, along with piston rings. They usually come with crankshaft bearings as well, although these need to be sized to the crankshaft. Some add valves, pistons, and other components, for those that need to replace these additional components.

Before selecting an ATV engine rebuild kit from an ATV parts shop or eBay, buyers should know the different levels of engine rebuilds, the major components that may be bad, and how to select the right kit.

Different Levels of Engine Rebuild

Engines are usually rebuilt for one of two reasons. The most obvious reason to build one is that the engine seizes, which means that it does not turn anymore, even trying to do so manually. In many cases, the engine may turn part of a revolution before it hits something that keeps it from going any further. An engine that cannot be turned over manually has something broken inside, most likely a piston connecting rod.

That is not the only time an engine may be rebuilt, though. Assuming that an engine never suffers any serious damage, like a broken connecting rod, the engine may wear out. This is usually indicated by the engine smoking a lot and losing power. Engines that reach this point in their life have lost a lot of their efficiency and need rebuilding.

Depending upon the life of the engine, the cylinder bore may need to be enlarged. This is referred to as "boring out" the cylinder. When this occurs, the pistons need to be replaced, as oversized pistons are needed, in order to prevent the pistons from "slapping" the walls of the cylinder. If the cylinders do not need to be bored out, then the same pistons can be reused.

It is usually impossible to tell whether the cylinder needs to be bored out or whether any major components need to be replaced, until the engine is taken apart. At that time, a visual inspection and one with micrometer measuring equipment is needed to tell exactly what needs to be done.

Major Engine Components That May Be Bad

While the rebuild kit has all of the necessary seals, gaskets, and bearings for the engine rebuild, they typically do not have any of the major engine components. So, in cases where the engine has become damaged, these parts may need to be replaced separately during the rebuild.



Action Required

Piston rings


Hole in the top



Loose in cylinder

Should slip in, but not have much room to move

Cylinder has been bored out and the piston is too small; replace with one that matches the bore-out diameter

Connecting rod (piston to crankshaft)

Engine manually turns part of the way around

Rod is broken, needs to be replaced; check crankshaft and cylinder walls for damage

Bearings and crankshaft

Grinding noise

Difficult to turn engine over manually

Scoring of the crankshaft requires having it reground by a machine shop

Valves and lifters

No exhaust or vacuum

Engine turns over too easy manually

Valves broken or stuck; rebuild head

Note that all of these actions are to be done as part of the engine rebuild. This information is given merely as a guide to help in troubleshooting.

Selecting the Right ATV Engine Rebuilding Kit

In most cases, seals and gaskets cannot be reused. Time, heat, and exposure to engine fluids cause them to become brittle and crack. When this happens, oil begins to leak and engine efficiency may drop. Any time an engine is rebuilt, all seals and gaskets are replaced. The least expensive way to buy these is to buy an engine rebuilding kit.

Engine rebuilding kits must be selected with care. It is important that the kit properly matches the engine, or it is not usable. This can be harder to determine with ATVs than it is with cars. Typically, car engines are made by the same manufacturer as the car, itself; however, with ATVs, this may be different. Some larger ATV manufacturers, or manufacturers who also build motorcycles, build their own engines. Smaller manufacturers buy their engines from an engine manufacturer or automotive manufacturer.

In the case of ATVs whose engines came from another manufacturer, information about the engine make and model should be available in the ATV owner's manual. The same engine is typically used for the entire year of a particular model's production, so it is easy to determine which engine model is used. Most manufacturers have this information available on their websites.

There are four necessary pieces of information which define an engine and are needed to determine the proper rebuild kit: vehicle make and model, vehicle year, engine size (in cc), and engine model.

If a buyer has all of the other information, but are missing the engine model, he or she can still find the engine rebuild kit. If he or she has all of the other information, except the engine size, he or she can also still find the engine rebuild kit.

Other Important Data for the Rebuild Kit

Unless the engine is being rebuilt due to a problem that caused an internal component to break, it is safe to assume that the engine cylinder has to be bored out, necessitating the replacement of the piston as well. Bore-out is done in increments of ten thousandths of an inch. The piston and piston rings are sized in this manner, being labelled as .020 over or 0.50 over. If it is the first time the engine is being rebuilt, the machine shop normally bores it out to .010 over. However, if the damage is severe, it may be bored out larger than that.

The other component that may need to be machined is the crankshaft. In a small engine, this also serves as the camshaft, so it may be identified by that name as well. When it is reground, it is ground undersized, rather than oversized. The same dimensional system is used to identify the size after grinding. Main and rod bearings must be purchased to that size.

In summary, in addition to the engine model and year information, there are two other pieces of information needed in order to select the correct rebuild kit. Those are the cylinder overbore size and the crankshaft undersize grind.

When buying the rebuild kit from a private party, they have already purchased it with a specific cylinder overbore and crankshaft undergrind. Therefore, it is essential to verify that those dimensions are in agreement with the needs of the engine being rebuilt. When buying from an automotive or motorcycle parts supplier, it is normal for them to customise the rebuild kit, adding the right size piston, piston rings, and bearings.

Buying ATV Engine Rebuilding Kits on eBay

While there are a number of places where you can buy a rebuilding kit for your ATV, eBay is an excellent source. The auction format allows you to compare rebuild kits from various manufacturers and suppliers, to find the exact kit that you need, at the best possible price. Buying the kit on eBay is a great way to save money, as eBay sellers list their wares at the lowest possible prices, to ensure selling their products.

eBay Stores

Many of the sellers of ATV engine rebuild kits on eBay are eBay Stores. This may be the Internet presence of a brick and mortar shop, or a seller who only sells on eBay. In either case, they are generally experts on their products, who can help you if you cannot find the exact engine rebuild kit that you need.

If you need assistance in selecting the right ATV engine rebuilding kit, you can contact one of these eBay sellers, and ask for their assistance. Most are prompt to respond, providing the expert information that you need in order to make the right selection.


Buying an ATV engine rebuilding kit provides all of the parts expected to be needed for a normal ATV engine rebuild. A typical kit includes all of the seals and gaskets, along with piston rings, rod bearings, and even new pistons. As long as there is no damage to the major engine components, this kit makes it easy to rebuild an engine.

Using a kit is much cheaper than buying the components individually. Even trying to save some components and reusing them is not cheaper than buying a rebuild kit. Gaskets and seals tend to dry and crack with age, so attempting to reuse them is likely to cause oil leaks.

When selecting an ATV engine rebuild kit, it is important to ensure that it is the right kit for the engine. Kits vary extensively, as they are designed to work only with a particular engine model. In addition to the make and model, the size and year are important information. Additionally, the piston, piston rings, and rod bearings need to be sized to match the boring of the engine cylinder and the grinding of the crankshaft.

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