How to Port and Polish a 2-Stroke Cylinder
2-Stroke Engine Cylinder Before PortingOne of the best methods of improving the performance of your motorized bicycle without buying high performance upgrades is porting and polishing your 2-stroke engine. While adding performance parts to a motor can increase speed, it's porting and polishing your 2-stroke bike engine that’s going to improve its performance regardless of parts. The great thing about porting and polishing your motorized bicycle engine is that it’s a reasonable and inexpensive way to boost your engine’s power. In this guide, we’ll talk about what porting and polishing are, and what you’ll need to properly port and polish your 2-stroke engine.

What Is Porting?

Porting refers to the process of enlarging and shaping the intake, exhaust, and transfer ports around the cylinder of your 2-stroke engine. As a rule, when porting and polishing your 2-stroke engine cylinder, you’re attempting to match the size of the intake manifold and intake port, as well as the exhaust manifold and exhaust port. The intake and exhaust ports are essential to the performance of your motorized bike. Intake ports take in air and fuel and mix them properly while the exhaust ports release fumes as efficiently as possible. Though engines try to do this process naturally, a ported 2-stroke engine will do it more effectively. This process is usually followed up by polishing, which smooths these ports to help air enter more efficiently and with less turbulence — we’ll get to that a little later.

Why Porting Helps Your 2-Stroke Engine

Porting helps motorized bicycle engines create more power, burn fuel more efficiently, and last longer over time. Here’s how:

More Power

How to Port a 2-Stroke Engine CylinderIf you enlarge the intake ports on your 2-stroke engine, they will be able to take in larger amounts of fresh air when the piston is compressed. This allows more air to be combined with the fuel within the 2-stroke engine, which means more of this mixture is burned, creating more pressure and thus more power.

Greater Fuel Efficiency

Larger intake ports allow air to enter your 2-stroke engine quickly. This makes it easier for the fuel to combine with the air, which improves the engine’s ability to burn this fuel. Just like porting the intake port helps a larger amount of air enter a motorized bicycle engine at a much faster rate, porting the exhaust port helps the engine expel fumes at a more efficient rate, as well. When exhaust gases are able to leave the engine quickly, it helps decrease backpressure, minimizing resistance and pressure loss. Porting helps make the overall process of burning fuel a much simpler, faster, and more effective process.

Increased Durability

Some amount of exhaust backpressure is necessary for an engine to run. Even then, lessening this backpressure by porting and polishing your cylinder keeps the engine from having to work too hard to eliminate fumes and exhaust gases. This decreases the wear-and-tear that a 2-stroke engine that hasn’t been ported would typically experience.

How to Port Your Motorized Bicycle Engine Cylinder

While porting and polishing your 2-stroke engine may be inexpensive, you will still need a few essential tools. In addition, you will also need to take note of a few key factors to correctly port and polish your motorized bicycle engine.


There are a few key tools you will need in order to port your 2-stroke engine cylinder.
  • Tungsten carbide bits: These bits are known for their hardness and durability, making them the perfect tool for drilling into your 2-stroke engine cylinder. It is recommended that you try 1/8th inch shanks by 1/4th inch heads in order to provide good access to the intake ports and exhaust ports.
  • Dremel Rotary Tool and Flex-Shaft AttachmentDremel rotary tool: A Dremel rotary tool is effective because it operates at a high speed rather than a high torque that comes from using a standard drill.
  • Flex-shaft attachment: A 32-inch flex-shaft attachment is used with rotary tools for porting and polishing. Dremel makes these flex-shaft attachments for its brand of rotary tools.
  • File: Using an 8-inch half-round file can really help you get deep inside the intake and exhaust ports so that you can fine-tune the port work on your 2-stroke engine. While it is not as efficient on its own as using a Dremel rotary tool with a flex-shaft attachment, it is helpful when used in conjunction with a Dremel.
  • Sandpaper: This is useful for rounding out the edges of your ports. You can also use sandpaper to rough up the intake, making it easier for your motorized bicycle engine to consume fuel. Extra-fine sandpaper works best for polishing jobs — for best results, it’s recommended to use 600 grit sandpaper, though 240, 320, and 400 grits work well, too.
  • Compressed air: You should use a can of compressed air to make sure there are no loose metal bits, filings, or other debris in your 2-stroke engine cylinder when you are finished with your port and polish job.
  • Sharpie or marker: You may want to use a Sharpie to mark your margins so that you do not shave off too much metal when porting your 2-stroke engine.


Porting and Polishing a Motorized Bicycle EnginePorting the engine cylinder on your motorized bicycle is quite simple. All you need is to grab a tungsten carbide tool with an extended shank, put it in the flex-shaft attachment of your Dremel rotary tool, and enlarge your intake and exhaust ports with precision. Use a 2-stroke engine porting guide to determine exactly how large you should make the ports based on the number of RPMs you want. The steps for porting your 2-stroke engine cylinder are as follows... 1. Put On Your Safety Gear Before you start doing any porting and polishing work on your 2-stroke engine cylinder, you need to make sure you are taking the necessary safety precautions. Wear gloves that will be thick enough to protect your hands from metal filings as you drill into the intake ports, but thin enough that they don’t compromise your ability to hold the engine cylinder and Dremel tool with precision and care. You should also consider wearing a pair of safety goggles for eye protection, but make sure your vision is not impaired so that you do not damage your intake and exhaust ports. 2. Thoroughly Clean the Cylinder Before you begin porting and polishing your 2-stroke engine cylinder, you need to make sure it is free of debris, oil, and dirt. Wipe the cylinder down or give it a quick rinse and dry before you begin the port and polish process. 3. Set Up Your Dremel Take your tungsten carbide tool and insert it into the flex-shaft attachment of your Dremel. If you would rather just use the Dremel without a flex-shaft attachment, that’s okay, too. Just make sure the attachment you use has enough reach to access the intake and exhaust ports in your 2-stroke engine cylinder. 4. Determine the Size of the Ports Sizing Manifold Port for Porting and PolishingBefore you start drilling, you need to determine how large the ports will be. This is simple: By lining up your ports with your gaskets, you can determine exactly how much you need to shave off your ports without ruining the 2-stroke engine cylinder. Try using a fine Sharpie to mark exactly how much to cut away. 5. Use Your Dremel Tool to Open the Ports Once you have set up your Dremel tool, you can now use it to carefully drill away at your intake and exhaust ports until you make them larger. Note: You’ll want to make sure that both the intake and exhaust ports are matching in size. Using the tungsten carbide bit, make sure you drill away at all sides of each port evenly and uniformly. If you grip the Dremel like a gun and move it around the inside of these ports intentionally, the carbide bit will shave away at the aluminum and increase the size of these ports. 6. Fine-Tune Your Port Work Use a file to scrape off any additional metal that you were not able to access with the Dremel. It’s a good practice to look at your ports from different angles to ensure that you shaved down each side of each port evenly. Note: As always, make sure that you are taking your time through each of these steps so that you do not accidentally ruin your 2-stroke engine cylinder.

Key Factors to Consider When Porting Your 2-Stroke Engine

Before you start porting your motorized bicycle engine’s cylinder, there are a few factors you should keep in mind.
  • Heating: If your ports are too large, the cylinder gets thinner, which increases the risk of overheating.
  • Cylinder distortion: When porting your 2-stroke engine, make sure you do not alter the cylinder so drastically that it is unable to make reliable contact with the engine’s pistons — this can lead to a decrease in power. Make sure everything is rounded out properly and that all edges are smoothed so that your piston rings have a good amount of clearance.
Remember that the changes you make to your intake and exhaust ports are permanent. It’s best to take your time while porting and polishing your 2-stroke engine. A job can lead to imperfections, so make sure to be precise and careful when porting and polishing your 2-stroke motorized bicycle engine.

Polishing Your 2-Stroke Engine Cylinder

Porting Process for 2-Stroke EngineIn order to maximize the benefits that come from porting your motorized bicycle engine, you should consider polishing the ports on the engine’s cylinder, as well. To polish your 2-stroke engine, you need to use fine sandpaper to round out all the edges on each port.

Why You Should Polish Your 2-Stroke Engine Cylinder

Polishing the intake ports on your motorized bicycle engine cylinder helps increase air intake and decrease the air turbulence and other factors that hinder the efficiency of your engine’s intake ports. Smooth intake ports allow air to enter the engine’s crankcase faster and more efficiently. This increases its ability to mix with the fuel, which helps it burn more efficiently. When you polish the exhaust port on your 2-stroke engine, you decrease the amount of carbon waste that can stick to it, which gets in the way of your exhaust fumes as they try to leave the engine. In addition, polishing these ports makes it easier to clean them if any residue does adhere to them.


Polishing your 2-stroke engine cylinder is even easier and much faster than porting it. To properly polish your engine, follow these steps... 1. Use the Dremel Tool to Smooth the Ports Moving the Dremel tool carefully, you can place the tungsten carbide bits into the intake and exhaust ports to shave away any flaky bits of aluminum and remove the little bumps and peaks within the ports. If you use an extra-fine grit, you can make the intake and exhaust ports a lot smoother. You should polish the intake and exhaust ports until they look smooth and shiny inside instead of rough and bumpy. 2. Use Fine Sandpaper to Smooth Over Imperfections Fine Sandpaper for Polishing a 2-Stroke EngineOnce your intake and exhaust ports are at the perfect size, you do not want to risk making them any larger during the polishing process. Use extra-fine sandpaper (600 grit) to smooth out any imperfections until you can rub your finger along the inside of the port without feeling any bumps or burrs. Note: While you can use fine sandpaper (240, 320, or 400 grit), extra-fine 600 grit sandpaper will give you the best results. Once you have smoothed over these imperfections, you can use a rag and some WD-40 to help these ports shine. 3. Clean Your 2-Stroke Engine Cylinder The last thing that you’ll want to do when polishing your motorized bicycle cylinder is make sure all of your aluminum dust and metal filings are out of the intake and exhaust ports. Be thorough and check your engine cylinder for debris, and make sure it is cleaned completely. If you want to be on the safe side, using a bit of compressed air to blow out any debris, dust, and particles is a great practice.

Should You Port and Polish Your 2-Stroke Engine?

2-Stroke Engine CylinderPorting and polishing your motorized bicycle engine cylinder will allow for increased fuel flow. This means you’ll get improved power and performance out of your 2-stroke engine as a result. Whether or not you should port and polish your motorized bicycle engine depends on what you’re looking to get out of it. If you want better fuel and air flow, as well as more power without having to purchase upgrade parts, porting and polishing your 20-stroke engine is a great option. Alternatively, if you do opt to install high performance parts onto your motorized bicycle, and also port and polish your 2-stroke engine, you’ll get the best of both worlds. Ultimately, porting and polishing your motorized bicycle engine may not be necessary, but it comes with some great benefits such as boosted performance and power, and better air-and-fuel flow.



excellent ! Thank you for the detailed method


Good info. Thanks.

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