Piston Not Moving Right

[tmcgradyr01]

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.

 

[Pablo]

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.

....the top piston ring snapped off but i figured it wouldnt rly affect the performance and continued.
.

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

 

[tmcgradyr01]

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?

 

[tmcgradyr01]

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.

 

[Cabinfever1977]

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.

 

[bairdco]

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.

 

[BarelyAWake]

The two little "ring keepers" BTW

 

[Gareth]

Rule number one when working on things mechanical. If it seems like it should go, and it doesn't, stop and determine why it is not going. Adding more force is not advised unless you are absolutely certain more force is required. It sounds like you forced the cylinder on without compressing the rings. You have likely scored your new cylinder with the piece of broken ring. You likely need a new piston, rings, and cylinder now. Also you will want to account for all pieces of the broken ring before reassembly. Look carefully in the case for any shavings with a good light. If any are present you need to crack the case and carefully clean everything before reassembly.

 

[Fossil]

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.
.

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

I just sneezed scotch out of my nose. That is definitely the best line of the year!

BTW Scotch out of the nose hurts a lot...

Jim

 

[DOC BOLM]

You guys dont realize that the bottom ring is called the J.I.C.ring In china.The bottom ring is there JUST IN CASE you take the top one out,kind of like a spare.H.D.

 

[Gareth]

You guys dont realize that the bottom ring is called the J.I.C.ring In china.The bottom ring is there JUST IN CASE you take the top one out,kind of like a spare.H.D.

See. I knew about the J.F.C. wrist pin retaining clips that most engines use...

 

[Dan]

I just sneezed scotch out of my nose. That is definitely the best line of the year!

BTW Scotch out of the nose hurts a lot...

Jim

, What is it with you and scotch in nasal passages!? lolol. I have to ask Carol if she got pics of that in Del. 2 funny

 

[Fossil]

, What is it with you and scotch in nasal passages!? lolol. I have to ask Carol if she got pics of that in Del. 2 funny

Hi Dan. That was the only other time it happened to me. This was real good stuff too. 16 year old Glenlivet. Natural cask strength. 120 proof. Wow does that burn the nasal passages!
Say hi to Carol for me.

Jim

 

[Dan]

Will do! Hoping to see you in CT this spring. (I will hide the scotch) ((Beer is much easier on the nose))

 

[tmcgradyr01]

You guys dont realize that the bottom ring is called the J.I.C.ring In china.The bottom ring is there JUST IN CASE you take the top one out,kind of like a spare.H.D.

So are you saying I can run the motor okay with just the bottom ring?

 

[DOC BOLM]

NO NO NO Both rings need to be on piston.H.D.

 

[Dan]

Have never tried running with only one ring but seems like a really bad idea. Wouldn't the spent gases have a straight shot and be forced below the piston? Would also think the piston would wobble and destroy the cylinder.

Asking, not saying.

Am sure you can get a set of rings lots of places, but Dax has em for 10 bucks.

ENGINE_KIT_PARTS_PAGE_2

 

[furament]

first motor i had smeered 2 weeks in couldent get parts cleened it up ran top ring and it ran for like a year in that tune never got another to run that way still need good rings

 

[Riding Rich]

The only time i broke rings was when the ring gap wasn't lined up with the keeper pins.
The piston should slide in easily.
Once you have it in the cylinder you should be able to turn the motor with a wrench very easily.
If not check it with the piston off maybe there is a bearing problem.

 

[Riding Rich]

Some engines do run with the top ring only.