What does it mean when the piston won't slide up and down? The piston and cylinder are smooth, no signs of trouble.

 

are you looking at the piston with the head off, or did you pull the piston to check it out? not clear from your post. If you are just looking down the jug with the head off, and the piston will not move,either a ring broke and jammed the piston in place, the crank bearings could have siezed,it is hard to tell without more info. Was it running before?,making noise, or smoking real bad? put out some more info, and I'm sure you'll get an answer, especially if Jack (LT80, bowing to the LT80 master) chimes in. Don't worry , I'm sure help is on the way.

 

We purchased this bike used for cheap knowing that it had problems. We did a compression test when we got it home and it had nothing. We took the cylinder off and it had the guages on the piston and cylinder head.

Got the head cleaned up and a new piston. It started up and we started the break in process.

The next day we went to started it and the the starter now makes this loud high pitched noise when you hit the start button.

Fearing the worst we took the head off again and the piston is still clean and cylinder clean but the piston will not go up and down manually.

So this is where we are at now. Any help would be great.

 

Thanks, that kind of info clears up a lot, if it was running,and now the piston is jammed so hard the starter can't move it,it may be a ring stuck in the wall, or since the engine top end was in bad shape, the crank bearing may have seized, this is hard to trouble shoot without seeing what is going on, the best thing I can recommend is doing a search on the forum for LT80, he is the most knowledgeable guy I know when it comes to small quads, especially the LT80,he does a lot of custom engine work, so he is the man to see.