The disassembly stage is a good time to review the condition of the engine and parts. As you are disassembling pay particular attention to any worn or damaged parts.
Before you go any further – wash your bike! Wash it thoroughly. When I’m doing this after I have given it a general wash I’ll remove the tank and plastics and then give it another thorough wash. you’ll need to ensure that you block the fuel pipe with a bolt and cover up the electrics.
This ensures that before you start dismantling you are less likely to introduce any dirt or debris as your engine is apart. Dirt and Debris is bad for engines!
Lets also use this as an opportunity to clean down your work area. You want it as clean as possible. I dismantle, inspect, work out what is needed in terms of replacement parts and work to the barrel etc. Then clean down again before starting the re assembly. I also like to start my re assembly on a clean rag – you’ll see in the pics!
Now do a compression test on your engine as it stands (unless it has lost compression) if you have good compression 120psi or above then when you have dismantled everything and confirmed that your cylinder doesn’t need extra work then the chances are that you will need to replace your piston with 1 of the same size as the one you are just about to remove. Remember this for later.
Remove the exhaust pipe; silencer first, usually 1 or 2 bolts and sometimes a spring or 2 connecting the silencer to the expansion chamber.
The expansion chamber will be bolted to the frame usually in 2 places, have a look around, identify where it is attached, unbolt it and then user your spring puller to remove the springs which attach it to the exhaust manifold. Once the springs have been removed you should be able to pull the expansion chamber away from the cylinder and remove it.
Remove the Carburetor (Carb); Loosen the jubilee clips on the air boot (back of carb) and inlet manifold (front of carb)
Rotate the carb so that you can remove the top of the carb (where the throttle cable goes in)
Remove the carb
*** Keep an eye on the inlet manifold for any tears or cracks in the rubber as an air leak here can be very bad.
*** If the rubber on the air boot is hard and you struggle to remove/reinstall the carb, carefully heat it up with a heat gun or hair dryer. The rubber will become soft and you should easily be able to remove / reattach the carb.
Drain the coolant (for liquid cooled engines):-
Remove the coolant filler cap
Find the drain bolt on the water pump housing (it should have a copper washer on it), use a jug or other container to catch the coolant as it drains out – careful as when you undo that bolt the coolant comes out pretty fast.
Identify if there are any other coolant drain bolts on the cylinder or head (they should always have a copper washer as a seal to prevent the coolant from leaking) , remove them if there are and use your jug to catch the coolant.
Undo the jubilee clips holding the coolant hoses in place on the cylinder, head, water pump etc. (sometimes you have to completely remove them, sometimes you can remove the cylinder while they are just detached) & remove the hoses.
It’s not likely that you’ll all be rebuilding the top end of the same kind of bike so the instructions that follow are generic. The differences between the bikes come down to the power valve assemblies in engines that have a power valve.
In most cases you need to remove the power valve cover and uncouple the power valve assembly in the cylinder from the power valve actuator arm, like I say there are a lot of different assemblies so I can’t go into huge detail here but I am working on individual guides for disassembling the different types of power valves on phoenixmotos.com so please check there in case I have already released the more detailed instructions for your bike.
Remove your cylinder head:
Unplug your HT lead / spark plug wire from your spark plug.
Remove your spark plug
If there is a head steady attaching the head to the frame, remove it.
Undo and remove the head nuts and washers, put them in a bag or other safe place and ensure that you know what they are
Remove the head
If there is liquid left in the cylinder from the cooling system then be very very careful not to let the liquid spill into the bottom end of the engine as you follow the steps to remove the cylinder
Remove the head gasket – in the case of a copper head gasket as you may be re using it keep it safe
Undo the cylinder nuts and washers – some engines only have head nuts as the studs go all the way through the cylinder to the end, if this is the case ignore this step. Keep your cylinder nuts and washers in a bag or other safe place.
Remove the cylinder – it should lift clean off with a little resistance sometimes a couple of twists are needed and others not.
You are now left with the conrod and piston and the exposed bottom end. cover the bottom end with a clean rag to ensure nothing can accidentally fall into it.
You now need to remove the piston from the conrod. First of all you need to remove 1 of the circlips from the piston. You need to be very careful as these circlips are prone to jumping out of the piston – use safety goggles! Make sure your rag is in place preventing items entering the bottom end carefully using a pick or 2 try to pry 1 side of the circlip up and out of the groove. Getting 1 end out will enable you to work the rest of it out.
Now you have removed the 1 circlip you need to find something to push the wrist pin from the other end out of the piston using your g clamp & a deep socket (or other item) that is just thin enough to slide past the circlip that is still in place & press on the wrist pin. A little trick here is to spray some WD40 into the area you just removed the circlip from – this does help to slightly lubricate the wrist pin as it begins to slide out.
Once it has started moving you need to find something that is wide enough that you can continue to press the wrist pin into – a deep socket is ideal here. Once you have pressed it as much as you can if it needs to go further it is likely you will be able to pull it that last bit with your fingers. If not a deeper socket is needed, usually once they have come out so far they will just pull out.
The piston and wrist pin should now just lift away and you should be able to take the little end bearing out of the conrod.
Disassembly complete