1. Remove the three nuts and one acorn nut on top of the head.
2. Remove the points cover on the left side of the head.
3. Remove the two screws that hold the points plate, and the three screws that hold the points base plate. You may have to use an impact screw driver to get some of the screws off.
4. The advance mechanism is under the points plate. Remove the alternator cover and use a socket to hold it stationary. Use another socket to remove the advance mechanism bolt on the camshaft end. Remove the advance unit, notice the position of the dowel pin. Remove the advance base plate.
5. Use the socket to position alternator flywheel to the "T" position next to the index pointer. The piston is at TDC, Top Dead Center.
6. Hold the alternator in place with the socket and remove the two bolts on the camshaft. Remove the camshaft. At TDC the dowel pin on the camshaft faces forward.
7. Remove the head cover and loosen the head from the cylinder. Use a rubber mallet if the head is hard to remove.
8. To remove the cylinder, undo the cam roller bolt on the left side of the cylinder. Remove the cam roller, then remove the cylinder. May have to use some rubber mallet persuasion for head removal.
- Keep the intake and exhaust parts separate.
1. Remove the rocker arm shafts and the rocker arms.
2. Using a valve spring compressor, remove the Springs, Valve keeper and the Valves.
Use a magnetic screw driver or similar tool to remove the valve keepers.
3. Remove the Oil Seal Cap and the oil seal from Exhaust Valve Guide.
4. Take out the valve spring seats from under the valve springs.
5. Don't forget to remove the exhaust and the head gaskets.
6. Clean the bare head before reassembly.
7. Re-assembly is pretty much reverse of disassembly.
Honda Used identical heads in all the Horizontal four stroke 90cc (89cc to be exact) engines. One of the few differences is the design of the copper head gasket. Some later models used a notched gasket to clear the mounting studs. Some of the real early heads had a wider base/gasket cutout and those heads can only be used with the matching cylinders. However all the internals were the same as the later models.
HONDA ATC90, CT90, CL90, ST90, S90, SL90 Head Rebuild