Seized piston rod

[The moped learner]

My friends moped piston rod seized up i tried everything to get it loose, it's like its bin welded on but i can rotate it 3-5 degrees before it locks up, has anyone had this happen to them? The crank rod is good so i don't want to spend money on a new rod. I had to cut the piston in half to make it easer to get to

[blue]

That will happen from time to time.but get it out may damage the wall of the motor so becarefull

[The moped learner]

What you mean

[The moped learner]

He's getting a 80cc BBK so he doesn't need the jug

[blue]

He's getting a 80cc BBK so he doesn't need the jug

OK never mind my bad.....................

[The moped learner]

But should i just give up and split the engine in half to get a new crank rod?😓

[zombie]

Sorry Bro!
Even if you get the pin out you will have to hone out the galling that locked it up, and that will oversize it.
If its a 10mm pin you might be able to get a 12mm piston/pin but that is the only option other than replacing the crank.

Whatever caused the failure will have undoubtedly created some issues on the big end as well. I'd scrap it.

[The moped learner]

Do you know where I can get a cheap crank rod?

[zombie]

Try one of these... HTTP://www.universalcrankshaft.com  One size fits all.

Sorry again dude... What bike is it. You said Moped?

[The moped learner]

Taotao vip 50cc could i drill it out till it thin so i can bend it useing pliers?

[245luigi]

Do it right the first time unless you want more headaches. I'd get a new crank

[zombie]

Lets just say you get it out... What about the scaring inside? It already took you longer to get this far than an entire rebuild would have taken.

http://www.ebay.com/itm/50cc-CRANKSHAFT-ASSEMBLY-FOR-SCOOTERS-WITH-4-STROKE-QMB139-MOTORS-/170930541326?pt=Other_Vehicle_Parts&hash=item27cc41130e&vxp=mtr

It's VERY easy to change. Take off the stator/variator. Remove the stator crank case half. Remove the oil pump because there is a bolt behind it. Split the main cases. swap the cranks.

I also highly recommend a new bore kit. The cylinder/piston had to get damaged when that seized up.

Big Bore Kit GY6 50cc to 80cc Scooter Moped 139 QMB 139QMB Cylinder Piston Rings | eBay
http://www.ebay.com/itm/Big-Bore-Kit-GY6-50cc-to-80cc-Scooter-Moped-139-QMB-139QMB-Cylinder-Piston-Rings-/221130667198?pt=Motorcycles_Parts_Accessories&hash=item337c6a34be&vxp=mtr

Install all new gaskets.

Complete Gasket Set GY6 49cc 50cc QMB139 Moped Scooter Roketa Peace Ice Tank | eBay
http://www.ebay.com/itm/COMPLETE-GASKET-SET-GY6-49cc-50cc-QMB139-MOPED-SCOOTER-ROKETA-PEACE-ICE-TANK-/201078096527?pt=Other_Vehicle_Parts&hash=item2ed130428f&vxp=mtr

It doesn't matter what size bore kit you get. They are all the same manufacturer/quality.
If you want help preparing the kit, post up, and I will help.

There is another thread here where I broke down the prep needed as well. Try searching qmb 139 bore kit / zombie. I just posted it yesterday or the day before.

[The moped learner]

Cant i just get the piston rod and replace it or do i have to get a new rod and crank!😁

[zombie]

I'm sure you can find a rod but to have the crank pressed, and balanced is not worth the effort.
Search FleaBay better, and you can find cranksets for 29.99 + free shipping.

It's not worth messing about w/ it. Hell you can buy a whole new engine for under 400.00.

[The moped learner]

Well he got a new engine A 110cc short block moped engine and installed it on a 50cc frame! Man that thing flys! Takes of like a rocket!