150cc GY6 engine smoking

[johan]

Good day to all

I need some help on the following issue I have encounterd on my sons GY6 150 CC 4 wheeler.

I removed the cylinder head for repairs to the sparkplug hole,and while the head was taken off i accidently pulled off the whole top assembly and exposed the piston that came out if the sleeve.
I battled a bit with the piston rings to get the piston back into the sleeve but managed to do it anyway.
The head came back from the repairs and i proceeded to assemble eveything again.

Once assembled and all put back together it would not start,i then had a look at the timing (which was way out!!),i sorted the timing out and got it started right after that,

Once started the bike smoked vey bad (white/grey smoke)

i read up on  piston ring clocking and the correct posistion of the gap of each ring.
i have lined up each ring as per what i have read up and saw on Youtube.
Put the motor back together and started it but its still smoking
(bike starts fine,idles fine and rides fine)

Any suggestions on what have may gone wrong/
Any help will be highly appreciated!!!
Kind regards - Johan

[GrumpyUnk]

How long did you run it after startup? It may take a while to burn off any oil on the cylinder walls or on the piston rings assuming you oiled both prior to assembly. You could have some oil gathered in the muffler that would take more time to burn off also.
Most times clocking doesn't cause a lot of problems as the rings rotate as the engine runs. Imagine a hula-hoop spinning to a stop and you have the general idea. If the gaps did line up, they would soon move out of alignment given the rotating rates are not exactly 100% the same(at least I would not expect that).
If you broke a ring, or gnarled up the oil control rings, you would likely not have it run well for the first and would likely have blue smoke for the second. Using synthetic, I am not sure of the smoke color.
tom

[Deleted]

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[GrumpyUnk]

No. No. No.
Removing the piston from the bore, i.e., removing the cylinder, does NOT mean you have to replace the piston rings. As the engine runs, the rings slowly rotate in the grooves. They do not take a 'set' being in one particular position, but move.
You should replace the base and head gaskets to insure sealing of the crankcase(base) and cylinder(head). Some gaskets can be reused, but it is up to your discretion.
For instance, a copper gasket can be softened using heat, and it will be totally re-usable. Plain metal gaskets are not as likely to seal, and fiber with fire ring may seal if they come apart in good condition.
Finding good fiber gaskets seems to be getting more difficult. My preference is fiber, especially for a BBK, as they cut the compression peak pressure a bit with their depth increasing the effective combustion chamber volume.
tom

[Deleted]

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[snaker]

Apr 13, 2024 20:46:59 GMT -5 @jjoshua20214 said:

From what I've been told in the past and from my personal experience, removing the cylinder completely from the piston and rings ruins the seal.
Yes, the engine will still function fine, but will burn oil and have less compression from the ruined seal.

Isn't it the same concept for engine break-in?
The cross-hone pattern in new cylinders help wear the new rings in, so the seal is created.
That is why is it known for engines to gain performance after break-in or run poorly/burn oil if not done properly.

I've never had any issues re-using visibly intact gaskets, although it is not a common practice due to the low price.

Also, from my experience higher compression led to greatly increased acceleration, just more wear on the bearings.
Ultimately it depends on how the carb and drive train are tuned.

I disagree with the cylinder losing the seal.
If a healthy setup is disassembled and reassembled properly, there should be no problem.

Multiple cylinder engines with individual jugs can be a problem if they are switched around at install.
Example: if #1 cylinder and #2 cylinder get switched.
Same thing goes if the pistons are swapped around.

I don't care to reuse gaskets.
Collecting the necessary gaskets is part of the job prep.

Some of the yard engines can be tricky if they have the two piece lower connecting rod.
On those you have to drive the piston into the cylinder from the top and you are messing with the cylinder top ridge.
That's somewhat more iffy.

[GrumpyUnk]

jjposhua saidL:"From what I've been told in the past and from my personal experience, removing the cylinder completely from the piston and rings ruins the seal. "

If you experience increased oil consumption and perhaps loss of compression when you reinstall the piston & rings into the cylinder, then more than likely the installation is not being done properly. Something is damaged during installation or the rings get damaged during removal or installation.
If you do some research, you may be able to find how piston rings move during use. The rings move in the groove. They do not sit still, EXCEPT 2T rings which are 'pinned' from rotation to avoid the possibility of hanging on the E/I ports. If they don't work right then something was done wrong as they do not care much about their position in the groove as they see the whole cylinder wall over time as they are used.
I did not know this until after working on engines for 40-50 years.
tom

[Deleted]

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[snaker]

Apr 10, 2024 15:37:36 GMT -5 @jjoshua20214 said:

One you removed the cylinder you ruined the seal. You need to replace rings and re-hone or replace the whole cylinder and rings.

You're the one who wrote this, aren't ya?

And there is no GY6 style engine design I know of that uses a 2 piece connecting rod.
Other small engines such as Briggs and Stratton do.
Just trying to clarify the difference for anyone who has seen such a thing.

[Deleted]

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[GrumpyUnk]

Apr 15, 2024 0:43:04 GMT -5 @jjoshua20214 said:

Apr 14, 2024 21:15:17 GMT -5 snaker said:

You're the one who wrote this, aren't ya?

And there is no GY6 style engine design I know of that uses a 2 piece connecting rod.
Other small engines such as Briggs and Stratton do.
Just trying to clarify the difference for anyone who has seen such a thing.

Yes I posted that.
Is there any reason why you are asking me if i'm the author of the post you are responding to?

As far as I'm concerned, this post is about a 150cc GY6 engine. I have no clue why you are talking about a lawnmower.
I think that information might be better suited for the "Off topic" section of the forums as it does not help the person who posted this thread or is relevant to a "4-stroke scooter or moped". 

  My comment is exactly contrary to your statement that disassembling a piston & rings from a cylinder REQUIRES replacing said piston and rings.
 You are welcome to know what you know.  I suggested research so you could determine if you want to stick by that statement or are willing to allow that R&R pistons can be done without the need to replace everything.
 You call it snide, and that was not the intention.  The intent was as above.  In general, do what you want, but I will counter what I think is incorrect information.

 Read what I read about experience:  I DID NOT KNOW THIS for a long time, and thought the rings were installed and did not rotate.  I learned different.  My experience mentioned how long I was ignorant, and does not reflect on you, your experience, your age, or anything else.
 Have fun.  I do not need to respond to people that disagree in a disagreeable manner and do not read what was posted.
tom

[Deleted]

*Withdrawn from forum* 

[GrumpyUnk]

Water over the bridge or under the dam.

I was unaware rings rotated in use. I imagine they move in a similar fashion to a hula-hoop on its last moves before coming to rest if spun. They kinda walk around in the very last movements.
As far as oil control and compression surfaces breaking in... newer rings(to my knowledge) can be chrome plated(ot other metal beyond Fe) which take a longer time to bed. To cure the time factor, makers put a very very very thin protrusion on the face of the ring, so all ring pressure gets concentrated on that very tiny lip, causing the lip to bed with the cylinder walls muy quickly. The rest of the chrome ring takes its time.
I am not a ring specialist, just picked up stuff over the years. I have read that some have installed new rings into cylinders that have not been 'deglazed' or 'honed' with reasonable success. I would still use a ball hone at least as I want the rings to scrape a little as they meet their match. Metal on metal with one surface almost mirror-like makes me think the non-mirror will just slide on the mirror, and not seal. I guess it depends on the surface of the ring, given the cylinder is pretty well mirror-like. If the ring is mirror-like, you'd have two mirrors... would they seal to each other? Depends on circular conformity. If both have the exact same diameter, one can imagine them conforming pretty well. If different, not so good, IMO.
Oil control is supposed to wipe in one direction - during intake or fire stroke movement. The rings and diagonal hone marks are supposed to leave a bit of oil between the marks. Some limited amount of oil film for the piston rings to rids upon. The piston is not supposed to be in contact with the cylinder wall(at least with any pressure), but will on the compression stroke be pushed to one side a bit by the angularity of the connecting rod and the rod journal as it goes past the 9 o'clock position on the upstroke. Diagonal, if you will.
It seems possible the 3-piece oil ring sets and get manipulated a bit during handling and installation moreso than the older style(cheaper) single piece rings. I do not know but guess the 3-piece thin rings can move or flex on the ring support that goes behind them. The rings seem to have a bit of gap so they are not exactly tied to the expander, and can move a bit, which I assume allows them to pull oil back down and hopefully not pull oil up to the combustion chamber or leave a too-think coating on the cylinder wall.
In the cases where you have had oil consumption after re-installing, what was the reason to take apart in the first place? What was the history, such as oil changes, overheating, etc? What consumption amount was measured?
Many think their engine does not burn oil. Well, they all burn oil, it is just the amount that differs.
The amount tolerated by the manufacturer has changed over time. Back in the mid-80s, a quart in 500 miles was deemed 'acceptable' for a new 2.3l Ford ranger. The owner had to do measurements over a specified mileage, and report. He ended up with a new shortblock. I think it was a quart in 200 miles... with no visible blue exhaust that I ever saw. Current values are in the 1000 mile range for 'acceptable' consumption.
The 139QMB and the larger model, may burn more/ I do not know as I change the oil more regularly than that, and have not had to add.
I helped re-ring a Ford 352 back when, and it burned oil after. Not great amounts, but likely a quart in 1,000 miles or maybe more. It was a bit disappointing.
tom

[90GTVert]

I'd just like to make it abundantly clear that if you remove the cylinder, you don't always have to replace the rings. You are not breaking a physical seal like a gasket, gasket maker, o-ring and so on. Going up and down the bore a million times, stopping and starting, experiencing temperature changes and so on is way more stressful than careful disassembly and reassembly of a top end.

That said, I'm not going to say that the OP's issue was not related to this disassembly and reassembly. It sounds like johan attempted to inform himself and do it right, but if you're new to engines (or experienced) things don't always go perfect. Engines can be pretty susceptible to issues related to seemingly small things like dirt/debris even and rings can be pretty fragile. There's also the possibility that it's a case of bad luck/timing. I've owned an engine that ran great and then suddenly started smoking during a ride (looking like I was fogging heavily for mosquitoes in short order) and didn't quit till I tore it down to install a new set of rings. I can't tell you for sure why it happened, but it certainly did.

Other thoughts related to the OP are that we don't know for sure that rings have anything to do with this smoke. First, you said it smoked after starting. Very common with a fresh start... depending on the exact amount/type of smoking. He said very bad, so probably not normal. Just in case though, I'd let it run for a minute. Could be that it had some oil in there from assembly and was burning it off when panic ensued and the engine was turned off. Also, piston rings are not the only thing that can cause oil consumption and smoking. The head was just back from a shop. Could be that the valve seals were damaged or something like that.