Occasionally when coming back down to idle from throttle, the engine will make a noise that it definitely should not make. I'm not sure how to describe it exactly, it just sounds very rough for a couple cycles and then smooths out to normal. But it's definitely not a noise it has made in the past. This happens usually when the engine is cold. As for when this started, I'm not really sure but I guess it has probably been in the past year so it lines up with the overall loss of giddyup.
I'm clearly not an expert but I checked all the things that were obvious to me. Belt was changed out not many miles ago. Airbox looked OK. I started looking up other maintenance items for high mileage bikes, and the thing that kept coming up was a top end rebuild. It made sense to me, that maybe the piston was just getting tired and it was time to change it out.
I put it off for many months but finally bit the bullet and ordered this $64 kit from Scooter Works: https://www.scooterworks.com/products/j ... embly-40mm and installed it on my day off, which was today.
I had done some research ahead of time, and I am pretty sure I got all the important bits, like getting the rings on in the correct orientation and lining them up with the pins to avoid them snapping. I did have a little oopsie, when I was lubing up the piston I accidentally dropped it about 6-12 inches on the garage floor where I was working. It looked fine, I wasn't sure whether I should be concerned or not, but I kept going because I only get one day off to do this (and my employer didn't even want to give me that) and so I felt a little under the gun. Also I removed the oil reservoir because it seemed like it needed to come off to get access to the head. I had not seen this covered in any of the material I researched but I just handled it in the way that seemed obvious to me. I drained the reservoir into some empty 2stroke containers I had laying around, and then put the oil back in as I was reassembling. Before I plugged the hose onto the stud where it came out of, I made sure oil was dribbling out of it so there hopefully wasn't any large air pocket in the system leading to a lubrication issue.
After full reassembly, I gave it a kick and it started up without much fuss. Now when I say not much fuss, I should also mention the carb bowl was empty, so there actually was a little fuss until it filled again. The reason for it being empty was because I had also been in there to replace a jet which I had previously cracked while doing a cleaning/inspection. The previous jet was left with just a couple threads to hang on, which is why I wanted to replace it. Both the old and the new are #80 jets, which I installed per recommendation by Scooterworks alongside an aftermarket exhaust that I had to install much earlier in the scooter's life due to the OEM one going bad early on.
Anyway, I let it idle for 10 or 15 minutes, then bolted the seat on and took it around the subdivision. I could immediately tell it felt draggy. When I pulled out on the main road I tried to baby the throttle, and let it creep up to speed. At about the 35mph marker, the piston seized. Now, I've never heard or felt what a piston seizure is like before, and no one had to tell me. I knew what had happened. It's an awful sound that made my heart sink. The bike started right back up, but seized again a little way down the road, so at that point I just turned around and putted back home. It seems like I can run it at 20-25mph, but for how long, I don't know.
While I had it running, I noticed it's still sometimes making that rough noise when coming down from idle. So whatever that is coming from, the top end kit did not solve it. Another thing I noticed was that it really did not sound good at higher RPMs. It sounded like metal on metal.
So now I'm left wondering what went wrong. Was it the cheapo $64 kit? Did I royally screw something up? Did I mess up with the oil and somehow cause a lubrication issue? Or is there a bigger problem going on? Should I be looking at the crank or crankcase? Could some other problem have caused my brand new kit to seize?
I don't really know what to do at this point. I don't want to buy a more expensive OEM kit if there is some other problem that is just going to cause it to immediately ruin yet another brand new kit. The answer, i know, is going to be take it to a mechanic, but I've been down that road before. The dealer where I bought it has never been super helpful with these things, but always happy to sell me faulty/wrong parts, etc. They just don't seem to want to deal with scooters. I could take it in for a diagnostic just on the off chance they have something useful to say, but it's a roll of the dice and probably will take them weeks to even get to it since they have real bikes to work on.
Is there any harm in opening the cylinder back up to see what's going on inside, and closing it back up with the same gaskets? What about getting a new gasket kit and putting the original setup back on? Is that an option? Maybe just a new OEM piston (~$22) instead of a whole kit? Any other last ditch thing I can try with the parts I've got, before I give up on it as too expensive for me to diagnose/fix?
I feel like I'm already out of the game with this one. This is my only vehicle, and I bought it back when I had money and a decent job. And now for the past several years I have not even made a living wage, so I have very limited resources to throw at it. The bike's been ridden daily since I first got it, even through sleet and snow. I feel like a part of me has died. At least it was getting me to work reliably before now, and even let me putt around the local college campus for fun. I really wish I had just left well enough alone.
I'll post some pics below of what I took out and what went in. I've been told that the cylinder looks good but the piston looks crusty.
But there is always something new I need to buy. One of these days I'm going to have to get one of those rolling mechanic's toolcarts, that would be cool to have around the garage.
