How to Rebuild a Two Stroke Engine

Two stroke engines are found in snowmobiles, ATVs and dirt bikes, chainsaws, weed eaters and leaf blowers. Some have a single piston while others have double or triple pistons. You'll need gaskets, pistons and rings for each cylinder, gasket remover/scraper, a cylinder hone and a parts cleaner solution.

1. Disassemble the carburetor and exhaust. Separate those from the cylinder head.


2. Remove the spark plug and take out the four bolts to remove the head plate and cylinder. Set those off to the side.


3. Remove the piston from the connecting rod. You'll need needle-nose pliers to take out the retainer rings in the pistons.


4. Stuff clean rags in around the connecting rods and remove the old gaskets from the top of the crankcase and the cylinder. This prevents dirt from falling into the crankcase.


5. Check for scarring or scratches inside the cylinder. Replace the cylinder if there are any. A cylinder hone will remove anything minor.


6. Use a light oil or soapy water to hone the cylinder, if necessary, and clean up everything around the crankcase and cylinder head. Place your new gasket on the crankcase.


7. Mount your new wrist pin, wrist pin bearings and piston on the connecting rod. Install the ring onto the piston. Spray or apply a thin layer of WD-40 or two-stroke oil onto the cylinder walls.


8. Start working the piston into the cylinder slowly and perfectly straight. If it is crooked, it will bend or snap the ring. Work the cylinder down into the crankcase and make sure the gasket is still in place.


9. Seat the cylinder down on the crankcase. If it's a single-piece cylinder head, make sure it is seated down. If it's a cylinder head with a cylinder plate, install the gasket, then the cylinder head plate. Insert bolts and torque down the cylinder head to the spec in a diagonal pattern.


10. Reinstall the carburetor and exhaust with new gaskets and put in a new spark plug. Inspect everything.