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Were you able to feel movement when it was the rod bearing? I can look at mine since my top end is off and the rod is sticking out of the crankcase. I grabbed it and tried moving it forward and backward but didn't feel any looseness between it and the crankshaft. The rod can be slightly moved side-to-side but I heard that's normal.

Also, since you have experience with taking the cranks out of these engines, is there anything at all you could think of that could come loose in there?

In a gy6 service manual, I see a diagram of an oil pump on the flywheel side of the crankcase. It shows a gear, a washer, a nut, O-rings and bolts around the oil pump. Makes me wonder if there's any chance something is worn or has come loose around that area and is making the noise. If so, maybe it's causing oil to not get pumped to the top end as well which would explain my sudden valve oil seal failure on the cylinder head.

By any chance, did you try grabbing hold of the crank and seeing if you could feel movement in the bearings when you had that problem? I ask this because I did take the flywheel off today and couldn't feel movement anymore. Maybe it's possible the bearings are worn enough that they make noise but aren't noticeably loose when the shaft is pushed up, down and side-to-side.

I noticed my spark plug was oily so I thought maybe a piston ring was worn or broken and that's how oil was getting to it and maybe even the cause of the noise I hear. However, I took the top end apart today and didn't see anything wrong with the piston, its rings or the cylinder walls. Only thing I saw was some slight scuffing on the piston.

Maybe it's getting in there from a bad valve stem oil seal. I had that happen before. Is there a way to test it? Could I pure oil into the intake port and tilt the cylinder head and see if the oil leaks out around the seal? The head has about 4,000 miles on it. That's pretty crappy if it's seals are worn after only that many miles.

I have to admit, it's getting embarrassing now. Any of my friends and family who know about this scooter look at me like I'm one of those pathetic men in a terrible relationship who just won't get out and keeps trying to make it work when it obviously won't.

I think it's also getting harder for me because I have had a 2012 Yamaha Zuma 125 for about three years now and have had zero issues with it. I bought it used for $2,099. If someone invested the amount of time needed to keep a Chinese scooter running into a minimal wage job, he could easily make enough money to buy a Japanese scooter and never have to deal with crankshafts and cylinder heads wearing out with less than a few thousand miles. You could probably buy a non-Chinese scooter from the 1980's for the same or less than a brand new Chinese scooter and it would last many times longer than a new Chinese scooter.

This has been ridiculous.

I ordered a camshaft and the seller sent me one for a 150cc. I had to return it at my own expense for a refund.

Finally, I got the right camshaft from a different seller and installed it.

I pressed the starter button... nothing but metal grinding noises from the starter clutch. Turns out the gear that's spun by the pinion gear on the starter motor was worn and so I ordered a new starter clutch.

A few hours after placing the order, I remembered that I still had an old starter clutch and decided to try it out. I knew if it still worked well enough to start the engine, I'd be able to see if the camshaft fixed the problem.

It did work and the engine started. However, the noise is still there so the engine is trashed.

I put in a request to cancel the order on the starter clutch but don't know if it's too late at this time.

So it's official - the crankshaft bearings are worn. I even grabbed the flywheel and pushed up, down and side-to-side on it and felt a little movement so I assume it's the bearings on the right side of the engine since I've tried this with the drive plate in the CVT and didn't feel any movement.

Now I need to figure out what I should do next. I don't care for fixing it or even getting a whole new engine since I'm disgusted with how many problems this scooter has given me during its short 6,000 mile lifespan. No one will buy a Chinese scooter that needs a new crankshaft, even if it is super cheap so I'm probably better off taking it apart and selling each part individually.

The parts are in and have been installed. It's weird, now I hear "a" noise but it's doesn't seem to be "the" noise that I had before. However, it's definitely coming from the clutch side so I know where to look.

The strange thing about the noise is that it's not constant. I hear it for a few seconds then it disappears for a few seconds than returns and so on. It does this at idle or when I rev it up some to get the back wheel turning.

Speaking of revving up to turn the back wheel, I think something is wrong with when my clutch engages, but I'm guessing it's because of the weights I put in. Not knowing what my old rollers were, I went with 7g rollers and now my rear wheel starts to move at about 2,500rpm when it wasn't until about 3,000rpm before. This would be fine except the engine likes to idle at around 3,000rpm until the choke is fully off and the idle speed drops to about 1,900rpm. It'll be like having the scooter stuck on cruise control until it warms up.

The gy6 service manual I mentioned before says the torque spec for this nut is 28ft lbs. That isn't all that much, especially compared to how tight it was on before. What do you guys usually torque it down to? I want to make sure it doesn't come loose when I finally get it back together.

Motonosity, a youtuber I often watch did a Honda Ruckus build series and he had this nut come loose.
You can hear about it at the 15:45 mark of this video.

With a 1/2 inch drive impact socket, 5 foot long pipe for leverage, spanner wrench wedged against the floor to keep the shaft from turning and a 210+lbs man sitting on the scooter to keep the scooter from lifting up off the floor by the spanner wrench's handle while turning the nut loose (which was still almost not enough to weigh it down), I was finally able to get the nut off.

Now I can take it apart and see what's wrong.