Piston Not Moving Right

So i had to replace my engine cylinder due to the hole's threads severing which led to not being able to attach the exhaust tightly.

i ordered the "80cc" 66cc head engine part from spooktoothcycle and the item arrived yesterday. in the process of switching the
engine cylinder, the top piston ring snapped off but i figured it wouldnt rly affect the performance and continued.

i had rly hard time fitting the new cylinder in. after i finished with the setup i gave my bike a go but the engine sounded very wrong.
upon disengaging the crutch, piston seemed to move up and down very sluggishly and pedaling was as hard as ever. i couldnt get
the engine started at all.

ive spent hours and hours troubleshooting bunch of problems so far and new problems seem to arise after fixing one thing.
i am rly frustrated and in the point of giving up.

please help, ive spent way too much time, money, and effort to give up on it.

Yeah, you need both piston rings. I'd bet that there's some hunk of piston ring that got jammed in between the piston and the cylinder.

You're going to need to take it apart and inspect it. You might want to bite the bullet and just buy a replacement engine, instead of replacing parts on a motor that's now been damaged twice.

Sometimes it's best just to start with a new engine. You can't break a ring and expect the engine to run worth a khrap, and you certainly can't troubleshoot other issues with the condition. Take a break, get back into it when you have THE true burning MB desire.

We had to wait until Christmas Eve, but it looks like we have the quote of the year!

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I don't think I have enough budget to buy a new motor at this moment. Couldn't I just buy a new set of rings and replace them on my own?

I need a set of instructions on how to fit the cylinder body into the piston so that I don't repeat the same mistake again. I broke off the ring when trying to jam the body into the piston body by hammering with the wooden end of a hammer. Is there an easy way to do this?

Take it apart first; you'd have to take it apart to replace the rings anyway. Remove the cylinder. Inspect the cylinder and piston for signs of damage. If you find no damage, you still need to figure out why the engine wasn't turning smoothly.

If you find any damage to the piston or cylinder walls at all, or any bits of metal down in the engine case (under the piston), don't bother fixing it; just get a new motor. This isn't to say that the motor you have can't be fixed, just that the cost in parts to do so would be approaching the price of a whole new motor. Another cylinder, a piston, set of rings, wristpin bearing, gaskets. And while you're in there, it wouldn't be a bad idea to replace your studs with better hardware.

You can learn to completely tear down and rebuild one of these engines. If learning that is your goal, and you have a high budget, buy all the parts you want, read a lot, ask a lot of questions, and take your time.

If your goal is to have a running bike you can ride around on, at the level of skill you currently have, a new motor is going to be the cheapest and quickest route to that end. You can always come back to the trashed motor later on if you want.

Luckily there is no damage besides the broken ring at the top groove of the piston. What I still don't understand is why the cylinder body won't slide on the piston smoothly.

How do you get the piston rings to stay inside the groove? They keep getting in the way of the cylinder body and somehow gets wedged in there.

The rings provide compression above (and in the case of a two stroke, below) the piston. They are supposed to be compressed in to install the cylinder over the piston, and then they spring out against the cylinder wall to make a tight seal, past which no air/fuel should pass. You need two of them, so that the gap in each ring can be in a different position.

I suppose it's possible that you got a cylinder that doesn't quite match the kit you bought, if you bought the kit one place and the cylinder another. I've only got the one of these myself, but from reading, different manufacturers' engine parts are not necessarily interchangeable.

Let's back up a second, though. What oil to gas ratio were you using to mix your fuel?

Maybe you can get a new set of rings and be really careful when you put them on.
Check you engine for damage first. find directions for installing you rings.

like Nougat said, you might have incompatible parts.

but the rings really aren't that hard to get in.

assuming there's no damage to the cylinder walls...

...you need to take a look at the piston and find the two little "ring keepers" in the slots. they're offset from each other, and it's where the open parts of the rings go.

when you have the rings lined up with the keepers, squeeze the top one together with your hand, holding it on the sides, and slowly work the piston into the cylinder. it takes a little concentration, patience, and a steady hand. you can wiggle it around, pressing in on the ring where you need to, and it'll go.

DO NOT FORCE IT. just finesse it.

once the top ring's in, hold the jug, squeeze the second ring the same way, and get that one in.

i usually pour a tiny bit, like a half a cap of 2 stroke oil into the cylinder now, right on top of the piston.

then, push the piston in as far as you can with your fingers from underneath, and mount the jug to the case.

you can hold the clutch in with one hand and spin the gear to make sure the piston moves.

also, if you've taken it apart completely, make sure you get the piston facing the right direction. your rings might hang up in a port if it's not.

hopefully, this made sense and you figure it out.

The two little "ring keepers" BTW