Guide To Four Stroke Motorcycle Engines, Part 7
When all diagnostic tests are completed and a top-end overhaul is in order, there is yet another decision to make before actually beginning. Should you remove the engine, or leave it in the frame? Many bikes require that the engine be out of the frame in order to remove the head. Fortunately, most bikes have plug connections for the electrical systems and other features. These make engine removal and reinstallation simple.
If you decide to leave the engine in the frame, be sure to clean away any dirt on the upper frame rails and the gas tank area so the dirt won't fall into the engine while you're working. Generally, a cleaner job can be done on a bench than in the frame, so let your available facilities dictate the approach you take.
After thoroughly cleaning the entire motorcycle, remove the engine in approximately this order of work steps and you'll stay out of trouble:
- Disconnect the battery and wires. Where wires don't have plugs, trace the wire to its end and tape a label on it to help you remember where and how to re-install it. Never snip wires and reinstall them with splices!
- Drain the engine, the primary, and the transmission oil.
- Remove the carbs or fuel injection systems from the engine but leave them attached to their cables. Wrap each in a rag and place them so they are protected until reinstallation.
- Remove the exhaust system - be careful of rusted bolts and nuts. (A little penetrating oil applied several hours before beginning this task works wonders).
- Remove the rear chain, or primary chain if the bike has a separate transmission.
- Double-check to insure that the only connections between the engine and the bike are the mounting bolts and plates. Make sure you remove all cables, lines, tubes, wires, ducts, covers, panels, and straps that connect the engine to any other part of the machine.
- Remove the mounting plates and bolts, then slip the engine out. Be careful! Engines are heavier than they look and often can be removed only from a particular side of the frame.
Cylinder Head Removal & Inspection
Having removed the engine from the frame, the next task is to situate it on a stand or fixture to steady it enough to work on it. A simple wood frame made from two-by-fours usually works well.
Begin by removing any electrical components on the head such as the points plate after you have marked its location with a lightly scribed line. On overhead-cam engines, first remove the timing assembly, cam covers, cam-chain tensioner, cam sprocket, and camshaft. After these components have been neatly stored away, wire up the cam chain. The cam chain is wired up to keep it from falling into case.
Now you can loosen the head stud nuts one half turn at a time each until they will spin off. Remove the head, being careful not to disturb the cam chain wiring or mar the head gasket surface.
Cylinder Head Service
Now that you've removed the cylinder head, clean it with solvent and give it a general inspection for cracks or other damage. Fill each port, one at a time, with solvent to check each valve's seepage. The valves that leak worst will require the most reseating effort. If they don't leak at all, they probably don't really need service at this time.