Flush with the successful removal of the clutch hub, I decided to move on and open the crankcase and see if I could figure out what that awful noise in the engine was. One thing I was not happy about was this play in the clutch shaft.. there's a good 0.6-08mm worth of in/out movement which is not really good. I check with the guys on a Facebook group (Yamaha two-strokes 1955-1979) and the consensus is that since this shaft is bolted up to the clutch hub and this did not exhibit any signs of wear earlier this was fine. I decided to proceed anyway since I was already halfway into the engine.
I removed the contact-point/coils plate and secured it so that it didn't hang loose. Next off was the gearshift stuff followed by the front sprocket.
This engine only hangs off two bolts. The lower one was removed earlier as it also secures the footrest assembly which needs to be removed in order to access the engine side covers. I put a stout screwdriver in there and removed the upper bolt. The screwdriver acts as a pivot and the forward part could then be lowered so that the weight was on the floor. Then the screwdriver was removed and the rear end of the engine was lowered.
The cylinder and its head was then removed. I did not remove it when the engine was installed on the bike as I figured the cylinder would give me something to grab, otherwise I'd be grabbing the studs and they're not really that sturdy!
With the engine off the bike and the cylinder + pistons off the engine it was then time to remove the screws holding the crankcase halves together but clean off all the crud that's on the engine first! You will need an impact screwdriver .. nothing else will work! I don't have the luxury of a workbench so two pieces of wood across a car tyre gave me the support I needed while allowing space for the shafts that poke out the other side. 30minutes with the impact driver got the screws out. Two did not co-operated and I had to resort to the chisel and whack those buggers around.
Once those screws were out (don't forget the two where the cylinder meets the crankcase) it was time to separate the case halves. There is usually a sequence for every engine crankcase build-up, ie you have to place all the components in one side and then lower the other half onto the positioned parts. On a crankcase that's split horizontally its a no-brainer as most of the time the parts go in the lower half and you place the upper half on top but on a vertically split case?What I've found is that generally the side with the screws is usually the upper case and when dismantling this side should face up. This YG-1 was the same. A bit of tapping around got the halves to separate without much drama. You need to remove the circlip next to the LH main bearing to give you clearance to whack the bearing out. I could hear some bits dropping inside the engine, more of this later.
I didn't get many pictures during the disassembly as my hands were too greasy but here are some pictures.
First pictures shows the left-side main bearing. The inner spacer has broken and while the balls are present they're just bunched upon one side. I think I've found the source of the engine noise!
Just below the center-boss you see a bit of wire thingy..thats part of the inner bearing spacer which broken into bits.
A closer look at the bad bearing.
Picture of the gearbox components..
Most of the parts are in good shape! Luckily as they're not many parts available locally!
The bike is really quite simple and not much can go wrong. I usually take a picture if I foresee that I may have a problem figuring out how something goes back together. This picture is of the kickstart ratchet mechanism. The only bit where I found necessary to take a photo on this bike! The curved portion to the left has ramps on which 5 steel rollers sit.
Remember the bits I heard dropping inside the crankcase when I dismantled the case? Well they were the rollers from the kickstart mechanism, eight ball-bearings from the gear selector mechanism and these...
I am fairly certain if I had continued to ride this bike it would have jammed and thrown me off the road.
