Motor Tear Down after crank got stuck

[heretolearn]

Hi there, I got this 80 cc two stroke I tore down to find out that the motor seized inside between the crank case and the crank. I believe what caused it was bearing failure but I did not see any broken parts when I took off the cylinder and Piston. I also noticed that inside the crank case it was bone dry. For future reference I ask if it would be ok to put a couple ounces of oil or some thing like pro long or dura lube for inside the crank case lubrication.

 

[Tool Maker]

What kind of oil were you mixing in your fuel? And what ratio?

B.

 

[tooljunkie]

for after overhaul,a dribble of either oil you mentioned wont hurt.be aware though,it will dilute with the air fuel mixture and richen the mixture,possibly fouling the plug.
a siezed bearing is most likely the cause,you can source the bearings from most auto/farm supply stores.change all the bearings while you are in there.

 

[heretolearn]

thanks for the help, I figured it out already. Only wish I knew how to delete this tread.

 

[littletinman]

What ended up being the problem?

 

[BoDean_LP]

I had a stuck crank too. I didn't want to do a tear down, so I figured I'd do what I could and replace the whole thing if necessary. To get the crank spinning again, I used a fairly wide hex-shaft screw driver along with an adjustable wrench on the screw that holds the little gear on in the gear box. I cranked until I almost stripped the screw, then the motor finally budged. I did this with the jug and piston removed. The crank was binding at a certain point of rotation, so I just kept working it back and forth, all the while spraying in a ton of WD40. (I know, not the best stuff for this application.) Eventually the friction lessened enough to spin the crank by spinning the rear wheel. I flipped her over and just started spinning the wheel. I had to unbind it every now and then. About a half hour of this later, I was able reassemble the motor and fire it up.

There is now no binding or apparent dragging due to whatever it is that was wrong.

I know this isn't the best method for fixing a motor, but you do what you gotta do with what you have to do it with, right?

 

[heretolearn]

The bearings that go the crank in the crank case were damaged from excessive speeding and also causing it to also damage the magneto. Basically my brother rides his bike like a motorcycle then breaks it and calls me to fix it. I have already rebuilt his bike 3 times. He has crashed it blown the motor and stripped the head bolts to name a few. I have all but lost my interest in motor bicycling since I built him one. I spend way more time working on his than I do on Mine. I forgot what it was to ride my bike. I put up a few pics here to show you my builds. The schwinn with the bike rack container is my Bike breaking Bros. The other is my own that rarely leaves the shed.