Track racing these bikes also has become very popular and more power is almost certainly needed to compete these days. Remove the bolt from the left side of the cylinder that holds the cam chain guide wheel, and then remove the guide wheel from the cylinder and the cylinder from the crankcase. Step 6. Watch the video above to see our Honda Grom intake and exhaust installation video. In this video and guide, we fit a KOSO big bore kit, which includes a four-valve head that will increase the cylinder bore to 170cc. Step 6. Watch the clip below to see the piston installation segment of our Honda Grom Big Bore Kit video. In this video and guide, we fit a KOSO big bore kit, which includes a four-valve head that will increase the cylinder bore to 170cc. Step 6. Install the new cylinder (included in the KOSO big bore kit) over the piston. Step 2. NOTE: Don’t lose the woodruff key in the crankshaft. Step 1. You no longer have to piece parts together with expensive components to get more power out of your bike. Remove the drain plug, then drain the engine oil and reinstall the drain plug. NOTE: The KOSO cam chain tensioner kit will withstand the extra loads that will be generated from the upgraded motor once the big bore kit has been installed. We are proud to introduce the first "all inclusive" big bore package for the Honda Grom! Install the new chain tensioner arm and collar (both included in the KOSO chain tensioner kit), and torque the bolt to 16Nm or 11.8 foot-pounds. Take the top piston ring and seat it in the cylinder using the piston. NOTE: For this project, you’ll need a well-stocked toolbox that includes a ratchet, socket set, wrenches, screwdrivers, a torque wrench and other essential tools, as well as the special tools listed above. Any engine running lean can have an immediate impact on your newly installed piston and cylinder. Step 4. Reinstall the two bolts mounting the left side of the cylinder head to the cylinder. Kits will vary in size, additi… Watch the clip below to see the cylinder head removal segment of our Honda Grom Big Bore Kit video. RECOMMENDED ITEMS FROM OUR STORE (not included in this listing), KOSO Performance Throttle Body  & Injector System. Intake manifold port is larger than stock. Step 2. Watch the clip below to see the cylinder head installation segment of our Honda Grom Big Bore Kit video. VERY IMPORTANT: ALL Big Bore Kits requires an Aftermarket Fuel Controller and A/F Monitor (not included) We highly recommend the Dyno Jet PCV, and WBC2 for proper control of the Fuel, maximum performance, and Longevity.

Step 9.

Next, remove the starter reduction gear and its shaft and collar from the left side of the crankcase. Set the engine to TDC (top dead center) by removing the cam cover from the left side of the cylinder head, then removing the timing cap and crankshaft cap from the left side crankcase cover, rotating the crankshaft counterclockwise until the T mark is in the center of the timing window and the mark on the cam sprocket is aligned with the mark on the cylinder head.