How To Plan A 2022 Honda Grom Engine Swap

Let’s be real for a second. The 2022 Honda Grom is an absolute joy to ride. It’s lightweight, nimble, and has one of the most distinctive sounds in the small-bike category. But despite all its charm, it suffers from a major limitation: the 125cc engine just doesn’t have the top-end power you might want for highway merging or spirited canyon runs.

If you’ve been thinking about a Grom engine swap, you’re not alone. The aftermarket community has practically standardized around this modification. Swapping the stock motor for something like a GXR cylinder kit or a full 200cc build transforms the bike from a cute commuter into a genuinely capable machine. However, this isn’t a weekend project for the faint of heart. It requires patience, specific tools, and a really good understanding of how these two-stroke engines breathe.

Choosing Your Power Path: GXR vs. Full 200cc

Before you start stripping parts off your bike, you need to decide on your endgame. There are two main routes most riders take when upgrading a 2022 Grom engine, and each has very different pros and cons.

The first option is the GXR kit. This involves replacing the cylinder and piston with an aftermarket 145cc or 149cc setup. The beauty here is that the crankcase remains stock. You keep the original engine block, which means less machining and fewer places for leaks to develop. It’s also significantly cheaper. You get a noticeable bump in top-end power, easily pushing the bike past the stock 60 mph ceiling.

The second route is the full 200cc swap. This usually involves a 200cc cylinder, a piston from a larger two-stroke (often sourced from other manufacturers), and potentially a new crankshaft to handle the increased thermal load. This build is more complex and expensive but offers a wider power band and better low-end torque than the GXR setup. It turns the Grom into a much more serious performer, though you will need to manage the heat output carefully.

Essential Components Beyond The Engine

Engine swerves are rarely just about the motor. When you increase displacement, the rest of the motorcycle needs to keep up. Ignoring these supporting components can lead to premature failures or a bike that simply doesn’t run right.

• Exhaust Systems: The stock muffler is designed for 125cc airflow. Swapping to a larger displacement means you need an aftermarket exhaust like a Termignoni or a Grom Performance system. These aren’t just for noise; they reduce backpressure and allow the engine to breathe freely, which is critical for making power.
• Carburetion: You cannot run a 145cc or 200cc cylinder on the stock carburetor. You’ll need to jet the existing CR27 carb heavily, or more commonly, swap to a larger carburetor. A CR38 or an aftermarket flat-slide throttle body can provide the precise fuel delivery needed for the increased airflow.
• Ignition Timing: Most modern Grom kits come with a different flywheel that has a new timing mark. Adjusting the CDI timing is crucial. Igniting the spark too early or too late can destroy your new piston. Make sure you have a service manual for the exact kit you’re installing to get these degrees right.

The Build Process: Key Considerations

When you’re actually breaking the bike down, take your time. The 2022 model year shares the same basic architecture as previous generations, so most online tutorials apply, but always double-check for any minor revisions in bolt patterns or mounting brackets.

Start by draining the fuel and oil. The two-stroke engine doesn’t have a separate oil sump, but it does have a pre-mix tank that needs to be empty. Once the bike is on a stand, remove the rear wheel, exhaust, and fuel tank to give yourself room to work. The cam chain tensioner and valve clearances should be checked and adjusted during disassembly. This is a great opportunity to ensure the head bolts are torqued to spec, as improper torque is a leading cause of head gasket failure in these high-strung engines.

Pay close attention to the crankshaft bearings during removal. If they are worn, now is the time to replace them. It’s cheaper to do it while the engine is apart than to risk a seized engine later. When reassembling, use the correct torque wrench specifications. The aluminum crankcase on the Grom can strip easily if overtightened.

Post-Swop Tuning And Break-In

Once you’ve got everything bolted back together, don’t just twist the throttle to wide open immediately. Two-stroke engines, especially modified ones, need a proper break-in period. Run the bike at varying rpm levels for the first few hundred miles. This helps seat the new piston rings and ensures the cylinder walls wear evenly.

Carburetor tuning is likely going to require some patience. Start with the manufacturer’s recommended jetting for your specific altitude and climate. Then, pull the spark plug after short runs to check the color. A tan or light brown color indicates a good air-fuel mixture. Black means it’s too rich; white or silver means it’s too lean. Lean mixtures can quickly melt a piston, so when in doubt, jet it slightly richer.

Is The Swap Worth The Effort?

For many riders, the answer is a resounding yes. The cost of a full engine swap can range from $800 to $1,500 depending on the kit and parts quality. Compare that to buying a used larger-displacement motorcycle that might lack the Grom’s unique character and agility.

Ultimately, a Grom engine swap lets you keep the bike you love while giving it the performance you’ve been craving. It’s a labor of love that rewards you with a machine that feels faster, more responsive, and infinitely more satisfying to ride. Just remember to respect the increased power and maintain the bike meticulously. Two-strokes are simple, but they don’t forgive neglect.