Problems after engine seizure

Hello,

So a couple of days ago my engine seized up on the road. Being the naive me as I was, I wanted to show everyone I can do highways, I killed my bike.

So here's how it all went:

Me and my friend, we were driving on the highway to a close by town to get his master brake cylinder. I went 25km at 85km/h on max rpm's (Yes, I know, that is really idiotic of me to do so, I have no idea what was I thinking at that moment). We just got into the town, as I was happily clapping my hands that we made it. I put my hands on the throttle once again (everything further detailing the seizure is far as detailed I could remember). The engine had a really small metallic crush grind sound and following the sound seized 2 strokes make. I understood, that everything just went 180°, and as soon as we stopped in a bus station, I checked if the engine wasn't cracked or leaking. It wasn't The pistons were stuck and I wasn't able to kickstart it.

Later, when the engine cooled at a parking lot, I tried to go back and forward with the engine being in gear. It turned! I could kick it, but with a lot more power needed than before. Then we tried to turn it on by pushing the bike. It made a really small amount of rpm's on full throttle and then died.

Once I got the bike home, we took a look at the top end. There were 2 really small pieces of metal torn off on the top of the cylinder. The upper ring was stuck, while the lower one was really open. One side of the wall was really slightly scratched between the rings and a bit below. The cylinder wall had also, a really small chunk of it out on one of the small holes (I don't really know how to call it). The crankshaft didn't really move on it's own, that was really surprising. What we noticed while replacing the cylinder, the left side of the crankshaft had a slightly lighter tape sized line, like if it was sanded with a 2000 sandpaper. I replaced my friend's piston (it was the same as mine) and tried to kick it, when put all together. It had the same resistance when kicked, as after the seizure. Had smoke coming out of the exhaust when push started. It would again, turn on at full throttle, have really low rpm's and then die.

People told us the main crankshaft bearing must be dead, but there was no clicking on ticking, just resistance when trying to kick. The bearings are, what I guess, the reason why it doesn't run on it's own. Could it be the side crank bearings? The main? Something else? Please share your ideas! I really don't know what to do. :/

Thank you for reading!

 

Did you flush out the crankcase before you put it all together?
An engine shouldn't seize because it's been ridden hard if it's set up right

 

Well, not yet. I blindly thought, that replacing the piston would fix it all. I had only a few hours on my hands. Me and my friend plan to take the engine apart in few days, since the summer solstice festival starts tomorrow. Will keep you updated!

Hopefully it's just a tiny lost piece of piston's metal, that sneaked next to the bearing and doesn't let it move.

 

The bearing will need replacing if it's been started with metal bits in the crankcase.
I did exactly this before, had a Yamaha jog or something for a top end rebuild,
I dropped a small piece of piston ring into the crankcase without knowing,
rebuilt the top,
Started it up, it ran great.
For 2 minutes.
Then it didn't run.
You learn from mistakes.

 

Will do so. Hopefully will get it running in a few days. Even though it's a moped, it really hurts if I can't ride it for multiple days.

Also, a small question. Should I put C3 or C4 rated bearings? Ofcourse everyone knows the answer, but the C3 are available locally, not so sure about C4. I plan to install 70cc when it arrives and sometime soon a Doppler Endurance crank, Stage 6 clutch, then file the 70cc.

 

Use the c3 if you are in a rush, and use good synthetic oil, don't use cheap own brand stuff.

 

Okay, thank you very much!

 

Okay, so I opened up the engine today. What I saw probably wasn't good. The crankshaft's main bearing contained bits of cracked metal and some kind of a bent ring, that was just spinning around. The rod was getting stuck too. The side bearings were okay. I guess I'll order a Doppler Endurance crankshaft, stage 6 clutch, C4 bearings and file the 50cc, until I get my 70cc.

P.s It's been 2 months now since I made the order for 70cc, scooter-attack.com still hasn't shipped yet. They don't respond to emails or phone calls. Wrote it would be shippable after 4 weeks since ordered. Sh*t, dunno what to do.

 

Holy shit. You are lucky it didn't bend the rod.
Was it quite knocky sounding, like a diesel almost?
I guess you need to be patient and hope they send soon

 

I know right, once I heard the sudden exploding metal grind sound, before the engine died, I thought I just heard my crankcase blast into bits. Once I saw no leaking oil I was really relieved.

Well, there was no knocking sound, since the bike didn't run on it's own. Just when pushed started, it was running on really low rpm's at full throttle. No knocking sound or anything abnormal. Maybe cause of my loud Yasuni R2 exhaust.