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April 2009
The engine strip down process is fairly simple and will be hassle free if a few simple steps are followed. Firstly, if the engine runs, start it and idle for about 5 minutes, then kill the engine and open the drain plug on the sump, watch out for the warm/hot oil and let it drain into a collection tray. Unbolt the oil filter and remove it also, again watch for hot oil.
One the engine has cooled down, unbolt all the pieces needed to remove the engine. That will mean the seat, petrol tank and side covers first to avoid cosmetic damage, then ignition leads, carburetor throttle cables, carburetor bodies, gear lever, kick starter, any other cables, ignition points lead and rear engine brackets. Remove the exhaust pipes and tacho cable.
Put a jack under the engine, using a piece of wood as a cushion and remove the front and rear engine mounting bolts, then the frame mounting bolts under the bottom case. The jack should now be able to lift the engine up without the bike coming along for the ride.
Get a friend to help maneuver the engine out the right hand side of the frame and place the engine on a suitable work surface.
Top End
Unbolt the cam cover and place the set screws into a zip bag with a note that identifies all the parts. Remove the gasket and throw it away, you cant re-use it.
Remove the cam chain tensioner, note I didn't remove the kick starter like I should have!
OK the gloves look poofy but it will help to keep everything clean as gloves are easy to wipe clean with a rag than skin which absorbs all the crap and gets real dirty real fast.
With the cam chain tensioner out remove the centre cam chain roller, be careful as it sits on rubber blocks that like to slip into the engine. This step will allow the cams to be removed next.
Unbolt the cam caps, they are under tension, so loosen each bolt a few turns then go to the next bolt so all four are done evenly and then repeat on the other cap so both caps on the same camshaft are undone at the same rate. If the cap lifts with the cam, apply pressure down onto the cap and continue to unbolt the caps until you can remove both caps and ensure that the bearing shells are intact with the respective cap.
Once the caps are removed, lift the chain up and remove the camshaft.
Note:
The caps are numbered so they must be returned the same way.
The cams are different so you cannot get them back in the wrong way!
I find the best way to store the caps and the cam is to mark out on a piece of cardboard the caps, their numbers and push them into the carb board so they stay in one place.
Note:
The Exhaust cam has a worm gear for the tacho, so you cannot get it wrong!
Repeat the removal of the cam caps, I also placed a threaded rod carefully in place of the other cam so the chain does not drop down the motor until I am ready for it to do so.
I use an air rattle gun to remove the cylinder head nuts, its quick, easy and full proof. There are 12 nuts to remove. Once off, put them into a zip bag, there are also two M6 set screws, one at each end of the cylinder head.
With the cylinder head unbolted, the nuts and two bolts bagged, I remove the rod keeping the cam chain from falling down and lower the cam chain down the tunnel, then I carefully lift the head up. If it wont budge, check that you have two bolts removed and then use a rubber hammer to give it a slight tap.
With the cylinder head lift away from the engine and placed on the bench, the old gaskets and cam rollers can now be clearly seen. Remove the head gasket and cam chain O-ring.
Lift the rollers out carefully, they it on rubber blocks that will fall into the engine if you are not careful.
Here is one of the cam chain guide rollers, its at the back of the engine block where the cam chain tensioner was mounted. Inspection reveals that the guide roller is worn and will need replacement.
Once the guide rollers are out and stored in zip bags, the barrels can be lifted up slowly and gently. The pistons should pop out and drop forward, if they dont something is seriously wrong!
When you tip the barrels upside down you will find a small cam chain guide, you need to remove this also.
With the barrels removed, the build up of dirt can clearly been seen, now is a good time to carefully clean up the dirt and oil. Stuff a clean rag in under each piston and wipe clean the grime around the engine case.
Next step is to remove the pistons, they are held onto the conrod via a gudeon pin which is retained by a circlip on each side of the piston. The circlip is a throw away item so a small screw driver can be used to lift it out of the groove it runs inside.
Note:
I didn't do to much cleaning on my engine as I disassembled it as I was going for a complete engine strip and because it will be going out for a professional clean after I wash the grease and oil from it. Normally a top end gasket replacement and a piston ring change would require you to be very careful not to drop dirt or parts into the bottom case. in this case, anything that falls into the engine now will be retrieved when the cases are separated.
Once a circlip is removed, the gudgeon pin can be pushed out. If its stuck hard they is a special tool that can be used to remove it. You can also use a threaded rod with nuts and washers to slowly move the pin out.
Never use a hammer!
Free at last!
Use a marking pen and write the piston number under the piston, then place the cleaned up piston into a zip bag with the gudgeon pin and write the number on the bag also.
Once all the pistons are removed, clean away the old base gasket, remove the two O-rings at the rear corner studs. Next remove the starter motor cover and put the set screws back into the starter motor. Then remove the oil pressure switch wiring.
Unbolt and remove the starter motor.
Unbolt the oil union pipe and oil pressure switch and place them into a zip bag.
Once you unbolt the union pipe, there are 2 O-Ring seals that will need to be replaced. When you buy a bottom end gasket set you should get these in it.
For the time being, put thee into the same zip bag as used to hold the pressure switch and alloy fitting so that you have a reference for later.
The next item to remove can be the crankcase breather, undo the centre bolt and then the top cover, inside is a plate with two Phillips head screws which also need to be removed. Put the plate, bolt and screws into a zip bag.
With all the items removed from the outside of the top case its time to work on the side cases, here I carefully remove the alternator. Then the starter motor gear drive is exposed, this can also be removed and put into a zip bag.
Moving to the other side of the engine, remove the points cover, then the points plate. This engine suffered some damaged to the points housing a few years ago, but I have a new one purchased fro $20 from eBay ready to go on.
Remove the clutch cover, then start on the kick starter, followed by the kick start cover.
These screws holding the kick starter cover were the only ones on the engine that are still Philips heads for some reason. An impact screw driver is the only way to remove them.
Normally a gasket sits here but I would say the previous owner didn't have one so this red goop is on everything...
Starting back on the points housing, removal of the mechanical advance mechanism and removal of the set screws that hold the housing is the last item on this side of the engine that needs to be removed.
A better picture of the damaged housing that will be discarded.
