I found the primary chain is a bigger problem than the cam chain, but here goes:
Changing the cam chain is not all that hard. As others have mentioned, you can do it with the engine in the frame, and you will need the appropriate size chain breaker (I got mine at a bicycle shop). There is one link in the chain that looks slightly different from all the others, and that is the best one to attack.
Remove the rocker cover. Remove the round left side engine side cover (the one over the ignition pick-ups). Useing a wrench on the square of the timing rotor, rotate the engine forward (counter-clockwise) until you spot the master link.
Remove the carburator bank. Remove the chain tensioner from the rear of the cylinder block. Lift the centre of the cam chain and lift out the centre guide. Look at the camshaft gears from the right side. At least one bolt on each gear cannot be removed right now. Rotate the engine backwards untill you can remove that bolt, then forward again so you can access the master link. Remove the remaining gear bolts.
Attach two pieces of picture wire to links on either side of the master link, and tie them off to something. (Trust me on this, you do not want to lose that chain down the camchain tunnel!) Loosen the camshaft caps evenly, remove the caps, and lay them out in order. They are marked with arrows and numbers etc, as shown in your Hayne's manual, but it's easier to lay them out carefully than to figure it out later. Remove the camshafts, keeping a firm grip on the gear, then the gear from the chain. (This is most easily accomplished by a trained octopus, or at least a helper).
Using the chain breaking tool, press one pin of the master link out enough to rotate the plates. Separate the chain. Attach the new chain to the old masterlink. You don't have to drive the pin back in, but rotate the plate back so it doesn't catch. Attach a third piece of picture wire to a link near the other end of the new chain. Pull the new chain through with the old. The weight of the chain should disengage it from the crank gear below, but if you find it catches, you can rotate the engine using the square on the rotor again. That's why you removed the camshafts earlier - the valves are all closed and cannot be struck by a piston. If for some reason the chains separate, that's ok, your picture wires will allow you to recover the chain and start again.
Once the new chain is through, attach a piece of picture wire to the new chain near the master link, tie off the wires, and remove the old chain. Using your chain breaker, join the chain with a NEW master link (again, trust me on this!)
Rotate the engine so the 'T' mark is aligned with the pointer. Re-install each camshaft so that the index mark (a little circular depression on the land of the camshaft just to the left of the gear) is exactly on top and the gear is sitting loose over the tunnel with the bolt holes lined up. Re-install the camshaft bearing caps and tighten gradually and evenly with a torque wrench. Install one bolt on each gear. Check that the index marks are still on top dead centre while the 'T' mark is still aligned with the pointer. Rotate the engine back 1/8 turn, then forward so the 'T' is again aligned. double check the index marks one more time.
Loosen the set screw on the chain adjuster, retract, and tighten the set screw (manual models) or remove the rear bolt holding the spring, pull back the ratchet tang, and retract the adjuster (automatic models). Re-install the adjuster with a new gasket. Loosen the adjuster set screw (manual models) or gently push in on the piston with a small screwdriver or allen key (automatic models) to take up some of the chain slack. Rotate the engine two full turns, and ensure the index marks are at TDC with the pointer aligned with the 'T' mark. Rotate the engine enough to install the other two bolts on the camshaft gears.
Rotate the engine so the 'C' mark lines up with the pointer. Tighten the set screw (manual models) or re-install the springs and retaining bolt (automatic models). Re-install the cover and carbs.
tafn
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