How should I install a new big-bore kit on my Zenoah or Chung Yang RC-style engine?
Here are some basic instructions to help you install a new big-bore kit or replacement top end for your motor:
1) Remove all outer engine parts from your current engine - remove the airfilter, carburetor and intake manifold; remove the engine shroud and ignition coil, disconnect the muffler, etc. The cylinder should now be bare with nothing attached to it.
2) Remove the cylinder by removing the bolts holding it to the crankcase. Gently slide the cylinder up and off. Remove the old cylinder gasket.
3) Separate the piston from the crankshaft. Remove the c-clips which hold the piston on the piston pin and bearing. Slide the piston off, and remove the piston pin, washers, and pin bearing if your kit includes new ones.
4) Put the piston ring on your new piston. Slide it down over the top. Be careful not to bend the ring or it may break. Make sure the gap in the piston ring is aligned with the little nub in the piston ring groove on the piston.
5) Re-connect the piston to the crankshaft. Make sure the arrow or dot on the piston is toward the exhaust (not intake) side of the engine. Make sure you have the pin washers at both sides of the piston pin. Install the c-clips at both sides to ensure the piston is securely attached. Make sure these clips snap securely into their grooves.
6) Place the new cylinder gasket on the crankcase. Slide your new cylinder down over the piston and ring. You may need to compress the piston ring slightly to get the cylinder on. Again, make sure the gap in the ring is aligned with the little nub in the piston ring groove. Slide the cylinder down slowly and smoothly. Try not to wiggle or twist it too much to avoid scoring the cylinder.
7) Reconnect the cylinder to the crankcase. Tighten the bolts firmly.
8) Reinstall the carb, filter, muffler, shroud, coil, etc removed in step 1. When reinstalling the ignition coil, place a business card between the coil and the flywheel. Turn the flywheel so that the magnets pull the coil and flywheel together, pinching the card. Now, tighten the ignition coil bolts. This will ensure you have a proper gap between the coil and flywheel.
9) Once all parts are reinstalled, fire up your new engine and enjoy your new, more powerful machine! Be sure to heat-cycle the engine several times (run the engine for a few minutes at a low, varied throttle, turn it off and allow to cool, then repeat) in order to allow the new parts to properly seat themselves.
