Pistons

Piston Kits for Scooters, Motorcycles and Small Engines

Easy Life Markets sells piston kits and cylinder kits for scooters, motorcycles, dirt bikes and other small engines, listed by bore size and engine type so you can match them to your motor. A typical kit includes the piston, a set of piston rings, the wrist pin and the circlips that hold it. Some kits go further and add the cylinder, the head and the gaskets.

What should you buy? If your engine smokes, uses oil, has low compression or has a scored piston, start by measuring the old piston or reading the size stamped on its crown. If the cylinder wall is also worn or scratched, a complete cylinder kit is usually the better choice. Our current range includes both types, and each product page lists the size and contents.

What Is in This Category

This sub-category sits inside our engine section, which is part of the wider auto parts department. It covers the reciprocating parts at the top of the engine: pistons, rings, pins, clips and the cylinder kits that include them.

Our current range is focused on small engines. It includes:

• The GY6 125cc piston kit with rings, pin and circlips, for the widely used GY6 scooter engine.
• The 64mm motorcycle piston kit for Zongshen 125cc and Lifan 138cc horizontal air-cooled engines.
• The 57.4mm scooter piston kit with an aluminium alloy piston, rings and pin.
• The SDH150 cylinder kit with a 57.3mm cylinder sleeve, piston, rings and cylinder gasket.
• The Yamaha PW50 60cc big bore kit with cylinder, head, piston, gaskets and studs.

We plan to add more sizes and engine types over time, including car and larger motorcycle applications. The guide below applies to piston kits in general, so it will still help when you shop for a different engine.

How a Piston Works and Why It Wears

The piston slides up and down inside the cylinder. On the power stroke, burning fuel pushes it down, and the connecting rod turns that push into rotation at the crankshaft. The piston has to seal against the cylinder wall, carry heat away from the combustion chamber and do it thousands of times a minute.

The sealing job falls to the rings. Most four-stroke pistons carry two compression rings and one oil control ring. The top ring holds back combustion pressure. The second ring helps with that and scrapes oil. The oil ring leaves a thin film on the wall and returns the rest to the sump. Two-stroke pistons usually have one or two rings and no oil ring, because the oil comes in with the fuel. The Wikipedia page on the piston ring explains the different ring types well.

Over time the rings lose tension, the piston skirt wears and the cylinder wall loses its finish. Overheating, a lean fuel mixture, dirty air getting past the filter and poor oil all speed this up.

Common signs you need new piston kits

• Blue or grey smoke from the exhaust, especially on acceleration.
• Oil use on a four-stroke, or oily spark plugs.
• Low compression on a compression test, or hard starting when warm.
• Loss of power that does not improve with a carburettor clean or new plug.
• Knocking or slapping from the top end, which can mean a loose piston or worn pin.
• Visible scoring on the piston or cylinder wall when you remove the head.

A compression test is the cheapest way to confirm the problem before you order parts. If compression rises when you add a little oil to the cylinder, the rings are a likely cause.

Types of Piston Kits and Cylinder Kits

Not every kit contains the same parts. Choosing the right type saves you a second order.

Piston and ring kits

A basic kit includes the piston, rings, wrist pin and circlips. It suits an engine where the cylinder is still in good condition and within its wear limit. You fit the new piston into the existing bore, usually after a light hone to help the new rings bed in. Our GY6, 64mm and 57.4mm kits are this type.

Complete cylinder kits

A cylinder kit adds a new cylinder or barrel to the piston and rings, plus the base gasket and often the head gasket. This is the simpler choice when the bore is scored, out of round or already at its largest size. It also saves the cost and wait of having a cylinder rebored. The SDH150 kit is a good example.

Big bore kits

A big bore kit replaces the stock cylinder with one that has a larger bore and a matching larger piston. That increases engine capacity, so the PW50 kit takes the engine to 60cc. Big bore kits often need carburettor jetting changes to run well. They may also affect whether your vehicle meets local rules for road or competition use, so check before you fit one.

Oversize pistons

Some engines can be rebored and fitted with an oversize piston, marked with the size above standard. This is common on car and larger motorcycle engines. If you choose this route, a machine shop measures and bores the cylinder to suit the exact piston you buy.

Piston Kits Compared

How to Choose the Right Piston Kit

A piston that is a fraction too big will seize. One that is too small will slap and burn oil. These checks help you get it right.

1. Identify the engine. Find the engine type or code. On scooters and small bikes, it is usually stamped on the crankcase. GY6 engines, for example, come in several sizes that look similar from the outside.
2. Measure the bore and piston. Use a bore gauge or calipers, or read the size stamped on the old piston crown. Compare it with the diameter on our product page, such as 57.4mm or 64mm.
3. Check the pin diameter. The wrist pin must match the small end of your connecting rod.
4. Check the ring count and type. Two-stroke and four-stroke pistons are different. Make sure the kit matches your engine.
5. Look at the piston crown and valve pockets. On four-strokes, the shape of the crown and the valve reliefs must suit your head.
6. Confirm what is in the box. Do you need gaskets, a cylinder, or just the piston? Read the contents list.
7. Compare the photos. Place the product photos next to your old piston and compare ring grooves, skirt shape and pin position.

If you are unsure about any of these, send your engine details and measurements through our contact page. We would rather check fitment before you buy.

Fitting Tips for Piston Kits

Top end work on a small engine is a popular home job, but it rewards care. A few habits make the difference between an engine that runs well for years and one that fails quickly.

• Work clean. Cover the crankcase opening with a clean cloth so circlips, dirt and gasket scraps cannot fall in.
• Check ring end gap. Push each ring squarely into the bore and measure the gap with feeler gauges. Compare it with the figure in your service manual.
• Fit rings the right way up. Most rings have a mark that faces the top. Stagger the gaps as the manual shows.
• Use new circlips and seat them fully. A loose circlip can destroy a cylinder in seconds.
• Oil the parts on assembly. A light coat of clean engine oil on the piston, rings and pin protects them on first start.
• Use new gaskets. Base and head gaskets compress once and are not meant to be reused. Our gaskets section has full sets for some engines.
• Tighten to the correct figures. Head nuts and bolts must be tightened in the right order to the torque in your service manual.
• Break the engine in gently. Vary the speed and avoid long full-throttle runs for the first period of use, so the rings seat properly.

If you have not rebuilt an engine before, or the engine is from a car, a qualified mechanic is the safer choice. Pistons on larger engines need precise measuring tools and service data.

Related Parts to Check at the Same Time

When the cylinder head is off, it is worth checking the parts around the piston. Replacing a worn part now costs far less than taking the engine apart again later.

Cylinder and head

Check the bore for scoring and measure it for wear. If it is past its limit, look at our cylinder and block parts. Also check the head for warping with a straight edge.

Connecting rod and crankshaft

Rock the connecting rod up and down. Any play at the big end means worn bearings. A worn crank on a small engine is often replaced as an assembly. Browse our crankshafts for examples such as the GY6 50cc crankshaft.

Camshaft and valve train

On four-stroke engines, check the cam lobes and rocker arms while the head is off. Our camshafts section includes the CG125 camshaft set and a motorcycle camshaft and rocker arm set.

Cam chain

A stretched cam chain on a small four-stroke causes rattles and poor timing. The motorcycle timing chain repair kit is one option, and more sit in our timing section.

Gasket sets

A full set like the Yamaha YZ125 gasket kit is handy when you strip the whole engine.

Two-Stroke and Four-Stroke Pistons

The engine type changes what a piston looks like and how it wears. Knowing which one you have is the first step in choosing piston kits.

Two-stroke pistons

Two-stroke engines use the piston to open and close ports in the cylinder wall. The piston skirt may have cut-outs or windows, and the rings are held in place by small pins so the ends cannot catch in a port. These engines fire every turn of the crank, so the piston works hard and runs hot. Many riders replace the piston and rings at regular intervals of running hours, as the maker suggests.

Four-stroke pistons

Four-stroke engines use valves in the head, so the piston crown often has small reliefs to clear the valves. There is an oil control ring, and the piston usually wears more slowly than on a two-stroke. Most scooter engines, including the GY6 family, are four-strokes.

Piston Materials and Build

Most pistons for small engines are cast from aluminium alloy. Aluminium is light, carries heat away well and is easy to machine. Cast pistons suit everyday use and are what most engines leave the factory with.

Forged pistons are made by pressing the alloy into shape under great force. They are stronger and handle more heat, so they are common in racing engines. They also expand more when hot, so they often need a little more clearance in the bore. For a standard commuter scooter or a youth bike, a quality cast piston is the normal choice.

Rings are usually cast iron or steel, sometimes with a coating on the face. Pins are hardened steel. Whatever the material, the fit matters more than anything else. Good piston kits are made to a known size, and the size is what you should check first.

Troubleshooting After a Rebuild

Most rebuilds start and run well. If yours does not, these are the usual causes.

• Low compression after fitting: rings may be fitted upside down, broken during fitting, or the head gasket may not be sealing. Recheck the assembly.
• Smoke that does not clear: a little smoke is normal at first as assembly oil burns off. Smoke that lasts past the break-in period points to ring seating or valve seal problems.
• Tight or seized engine: clearance may be too small, or the engine ran lean. Stop and inspect before it gets worse.
• Ticking or slapping: check the circlips and the pin. Also check that the piston is the right size for the bore.

Care and Prevention

New pistons last much longer when the engine is looked after. These habits protect your new top end.

• Keep the air filter clean and well sealed. Dust is the fastest way to wear rings and bores.
• Use the oil type and change interval in your owner's manual. On two-strokes, mix the fuel at the correct ratio.
• Fix lean running quickly. A lean mixture makes the engine run hot and can melt or seize a piston.
• Let the engine warm up before hard riding, so the piston and cylinder expand evenly.
• Watch the spark plug colour. It tells you a lot about the mixture and the condition of the engine.

Buying From Easy Life Markets

We list every kit with its size, engine type and contents, so you can see what you are getting before you order. The current price and availability are shown on each product page. If a kit does not suit your engine, our return and refund policy explains the next steps. For delivery questions, see our shipping policy.

These kits suit scooter owners, small workshops, dirt bike riders and anyone keeping a small engine running for work or fun. They are also a good choice for rebuilding a project bike on a budget.

Frequently Asked Questions

What comes in a piston kit?

Usually the piston, piston rings, wrist pin and circlips. Cylinder kits also include the cylinder and gaskets. Each product page lists the exact contents.

How do I know what size piston I need?

Measure the bore or read the size stamped on the old piston crown. Then match it with the diameter listed on our product page.

Can I fit new rings without replacing the piston?

Sometimes, if the piston is in good condition. On small engines, a complete kit is often only a little more and replaces every worn part at once.

Do I need to hone the cylinder?

If you reuse the old cylinder, a light hone usually helps new rings seat. A new cylinder from a cylinder kit does not need it.

Will a big bore kit need other changes?

Often, yes. The carburettor may need different jets to match the larger capacity. Check the engine runs at the right mixture after fitting.

Do you have piston kits for cars?

Our current range is for small engines. We plan to add more, so contact us with your part number and we will let you know.

Where can I find more answers?

Our FAQ page covers ordering, payment and returns.