Engine dismantling and diagnosing.

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.

Clutch hub.... Success!

I posted last week about a stubborn clutch nut and got some feedback from the Yamaha facebook group. I put the bike in 4th gear and used my socket with extension bar and still couldn't get the nut to move. What I really needed was an impact wrench but my compressor was 50 miles away in my other home.

There are electric impact wrenches which have become popular recently , I've seen the ads in my fb page, and I was toying with the idea of getting one. I got off work a bit early on Friday and on the way back I stopped by a hardware shop near my house and they had a promotion for power tools. The promotion was for an unheard of brand called DCA which is from .. China! Well for the limited used that it will see I think it should be fine. At around USD75 its not too expensive.

I got home and hooked up the e-wrench, on the second press of the trigger the nut unscrewed right off! Next was the crankshaft gear nut.. one more press of the trigger and it came off (left-handed nut). Should have gotten one earlier, would have made life easier when doing the brakes on the MB!


Here's a pic of the right side of the engine with both the clutch hub and crankshaft nuts removed.

I tried rocking the clutch shaft, not much where present. That sound is basically the front sprocket moving the drive chain and taking up slack.

And this is the tool I bought. Not bad at USD75.

Next is to get the stuff on the left-hand side of the engine off. Flywheel, contact-point/coil plate, gearshift stuff, front sprocket (another opportunity to use my new tool!) before I drop the engine to get deeper.

Trying to solve the engine rattle.

Well I've finally decided that the engine is too noisy and that I need to take a closer look at whats going on inside.

Since the engine was running I started it to warm up the oil before draining it. Theres not much oil.. about 500ml is what it takes.

Next job is to remove the footrest, you need to remove the 14mm bolt (which has a 14mm nut on the other end) and 12mm bolt which bolts in the body. Yamaha conveniently mounted the main stand on the body so you can still work on the bike without resorting to other methods to keep the bike upright. Once the foot rests have been removed, you need to either remove the exhaust or remove the right footpeg rubber. I decided to remove the exhaust as its simple enough.

I then removed the outer cover, this reveals the carb, clutch actuator and two-stroke pump. These are easy enough to remove. The hose needs to be pulled out of the oil-pump and withdrawn from the airfilter base. a bit of oil will come out, raise the end of the hose higher that the 2T tank (or oil level in the tank and the oil will not flow. I secured it to the oil-tank knob with a zip-tie.

Once that is done I removed the inner cover, bit of oil will leak out so have some newspaper handy. This will reveal the clutch. There are six bolts .. remove these evenly with a 10mm wrench. You will notice some rubber spacers between the clutch plates, these can be gently peeled off. Next you will find a 20mm nut which holds the clutch hub to its shaft. This is where I get stuck. On most bikes you will hold the clutch basket with a simple tool but here you need to hold the hub stationary while turning the bolt. I can get the hub to stay in place by putting the bike in gear and jamming the rear wheel but these bikes are lightly built and there is a strong possibility of breaking something. I probably need to make a holder which bolts onto the six screw-posts in the hub. Anyway I'll stop here and check around before I break something.

Here's some pictures of the clutch basket and hub.

Stay tuned!

Well it runs but....

It still is not as powerful as it should be. I know its only an 80cc and I'm not really expecting 100mph from it but it struggles to climb the slopes in my area and I believe its not giving 100%.

The first thing I noticed is that I'm not getting the required gap at the points even with the points base plate at the furthest end of its travel. On inspection I found the points cam (which is built into the magnet/flywheel) has worn to the extent where there is an apparent lip where the points foot doesn't not rub. This will affect timing and there's no point checking on other stuff until I fix this! 

Below is the inner part of the flywheel and you can see the little ridge the points heel has worn into the metal.

1. Looking thru the slots in the flywheel you can see the edge on the lip of the centre boss.

There's a brand new one on ebay for USD216 at the moment .. gulp. But hang on.. there's a used one for USD34.74 plus USD32.50 for shipping. In the description the seller notes "No pitting of points cam. Puller threads are straight. Good, useable condition.'' . Well the seller 'çycleheapsalvage' has more than 24k of mostly positive feedback and he does address the most common failure area on these flywheels so I took a gamble on it.

Looks about the same as mine. There is a stamped M - 5 on the raised squarish part. On the flywheel from my bike it is M -9. Probably balancing  info. 

 The keyway looks good, no wear.

And most importantly the cam is practically unworn, no trace of the ridge like on my original flywheel. 

 And no ridge on the edge of the inner boss.

 Installed the flywheel and snugged it up. You need to have a proper holder to hold the flywheel while you do up the centre nut but I improvised 😊! A 3/8 socket bar with extension braced against the floor!

Here's a picture of the bike running. I took it for a spin and it definitely pulls harder and sounds better.. still sounds like a bucket of bolts though.

The clutch is still weak... with the slightly higher compression it's that much more difficult to kickstart. I have new plates, clutch basket so I need to take a look at that.

The plugs are also oily, this could be due to worn crank seals.

So looks like the next plan of action will be to pull the right side clutch cover off and have a look at the clutch.

Might take a while though so please be patient.

Weird screw.. fix and bike running.

The screw I had problems with in the last post gave me a bit of a headache. At first glance it looks like a normal M5 fine..ie a metric pitch between the threads and a diameter of 5mm.

I went back to the shop I bought the wrong screws from and they didn't have a correct one. I went to a few others that I knew of and nobody had this particular size. One guy was more helpful than the others and took some time to measure my bolt up, he ended saying that it was probably a 1BA thread. Well we've been metric in Malaysia for a long time and none of the shops I went to had anything which fitted (these were all shops that only sold nuts/bolts and other fasteners). A quick search of 1BA bolts/screw on ebay showed a few examples but these were quite expensive! I was looking at something like USD30 (incl s and h) for a couple of screws. I posted my problems on the 'Yamaha two-strokes 1955-1979' facebook group and got some great input. I think the consensus is that Yamaha used some JIS threads.

The next option was to call a friend of mine who had a machine shop,  as the threads were ok I figured he could weld some metal on the end and chuck it in a lathe and make the chamfer. Once done all that was left to do was level the end and cut a slot for a screwdriver. He was willing to do it but his place is not really nearby and he doesn't work on weekends.

I thought about it for a week and finally decided to take the most convenient option.. run a M5 x 0.8mm tap down the hole and hope that it would hold the M5 screw I bought earlier.

Taking the bull by the horns, I brought out my tap and slowly worked it in. There was no space for a proper tap-holder so I had to use a pair of vice-grips (mole-grips) to screw it in. This had to be done slowly and the tap needs to be withdrawn after one turn to clean the threads. I believe the holes go through into the crankcase and I didn't want to get any metal shavings in there! So and easy does it.

I used a thin rod with a blob of axle grease and poked it into the hole so that the shavings would stick to it and get drawn out. This is what comes out.

Trial fitting of the new M5 screw.

And this is most of the stuff out.. this will cause real carnage if it gets inside the crankcase as the main bearings sit just behind this.

Threads were finally done and a trial fitting of the screw is snug. It doesn't really take much load as the stator-plate is well supported on the sides by the crankcase casting, the main force will be in preventing the plate from spinning.. in this sense I think its fine.

Here it is installed. Above the screw just visible on the edge of the stator plate is an alignment lug cast into the crankcase, this ensures that the plate is mounted centrally. On some bikes the holes in the plate are slotted so you can play around with the spark advance if the contact point mounts do not give enough range of movement, here it is fixed. I will probably come back and check the screws after riding a few miles. If it gets loose then I'll probably need to use some thread-lock or JB-weld.

This option of tapping the holes to a different thread is really a bodge and is something I really don't like doing but the other option would simply take too long.

Here is a video of the bike running.

It has more compression and power than before (not surprising considering the condition of the bore previously!) and the increased compression has made the slipping clutch more apparent as it sometimes slips when kick-starting.

Unfortunately the noise in the crankcase is still loud so it will definitely need to be investigated.. currently sounds like the proverbial 'bucket of bolts' .

Will ride it a while and see.

Cheers!

Top overhaul

Well while waiting for the standard size piston purchased from ebay (shipped from the US), I decided to proceed with installing my old cylinder which has now been rebored to +1.75 with matching pistons and rings.

I'll bee needing these ..

Piston, rings, head bolts, piston pin, piston 

bearing, circlips and a gasket set.

Since the cylinder was off the bike, I decided to clean up the crankcase gasket surface, removing the old gasket material. Well this should have been easy but the cylinder studs got in the way... so I removed the studs to enable better access. Bad idea. 

The first three studs came off fairly easily with two nuts locked together but the fourth didn't want to play ball. A bit more force (yeah I should have know better!) and the stud broke off at the base!

Well I stopped for a while to look at my options. The usual course of action would be to drill down the middle of the remaining portion and then use an easy-out. I really dread using this as my success rate is less than 50%. Second option would be to take the engine out and bring it to someone who actually knows what they're doing.

Trying to put off making a decision I looked around the bike and I noticed the Phillips bolts holding the coil mounting plate had butchered heads. Since I had my tools out I tried to remove them with my impact driver.. well I made things worse! The Philips head was totally rounded out even though I was using the correct bit! Well at least this was something I could solve as drilling down Philips screw/bolts is easy as the damaged area will centre the drill bit. This went well and the plate came off and the threaded remnants of the bolts unscrewed easily.

Since I had the drill out I decided to try my luck on the broken stud. Since the break was reasonably flat I had a good chance to get the bit smack in the centre. You don't want to drill off centre as it will damage the threads in the casting! I started by centre-punching the broken-off stud and mounted a 2.5mm drill bit into my trusty Bosch hand-drill. oh-oh.. the front wheel and mudguard was preventing me getting a straight shot at the stud so that had to come off first!

 
The 2.5mm drill bit made a nice hole..centred well too and was followed by a 3.2mm bit. When it got to around 5mm deep I inserted the easy-out. (If you're not familiar with these they resemble a big left-handed screw and the idea is they will screw into the nice hole I just made and reverse the broken bit out. Nice in theory but what can happen is they break inside the broken piece and now you're really screwed as the easy out is made of hardened steel and you cant drill it out). I tried to move the easy out but it was stuck fast. I then heated the crankcase where the stud was mounted to see if that would help (actually this is what I should have done initially when faced with the stuck stud) and with a bit of force the broken stud unscrewed.. Really dodged a bullet there!

I then installed the piston, cylinder and head... damm the gasket set does not fit! I made a new base gasket from gasket paper and re-used the head gasket. One tip when cutting gaskets is to use a hole puncher at the corners. I had one made for leather which has several sizes. Once you've made the holes all thats left is to cut reasonably straight lines. In the picture below it looks weird because the paper is not flat!

When it came to re-install the coil-mount plate I hit another snag, I had bought 2 bolts with a countersunk head but these would not screw in. I then compared new with old and the threads were different! As this was late evening on a Saturday the shops had closed so I put everything away.

To be continued!

Rebored Cylinder with 1.75 oversize

Continuing on my YG1 engine.

In my earlier post I mentioned I found a NOS standard cylinder but the vendor only had a 1st oversize piston (0.25) over. I managed to find one on eBay but they wrongly sent a 1st oversize one. They were good about it and are sending the correct one but the wait is tough as its usually 4 to 6 weeks from the US to Malaysia.

If you remember I mentioned that the local bike shop said they could rebore my bike to 1.50 over..well I sent them the cylinder and old piston and I got them back 2 weeks ago. The new piston quality is not too good as the crown is pretty rough with one or two bumps from the casting process.. It also looks like the guy who did the rebore sanded the skirts a bit. Good sign as he probably checked the fit of the piston. The rings are unbranded.. They just have "trim 1" and "trim 2" marked on them.. I'm gonna install trim 1 top and trim 2 bottom unless anyone has any better ideas?

The rebore was supposed to be to 1.50 over but they ended up having to do 1.75 as the bore was too damaged to do a 1.50. Looks like it was done correctly as the piston sits square in the bore with minimal rocking.

Piston. you can barely make out 1.75. Arrow points to exhaust port. Get this wrong and the bike won't run.

Nice and new.

The skirts are sanded a bit.

Rings. also marked 1.75. Trim 1 will go in the upper position. 

Bigger bore.

I'll probably install it this weekend and hopefully get to ride it. Will keep you guys updated.