Chinese engine failure after 1300 miles - Tried troubleshooting root cause unknown -

djsalto

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Hi guys, I am little concerned about what happened to my first 65cc chinese motor. I use it to do 15miles/day and the engine started to lean out...
I noticed that by the way it started to work after riding for a half an hour.... it started to loose power and Im very concerned about what could fail.

After this the engine won´t started again, started to troubleshoot:

-Checked spark plug (spark ok) but it was dry (ngk b6hs)

-Tried a new one just in case: nothing happened

-Took out carburetor cleaned it up and tested again -> nothing

-Tried with a spare carburetor and then improved very little: Spark plug was wet, but engine was still not starting giving a few plops and i needed to rev. up the motor by pedal...

-Gaskets in good shape....

-Noticed loss of copression but it still was having some (compared it with a brand new motor)

-Also i supose by loss of compression: If i put my hand over intake port (tapping ig) and I move the motor no notice of suction as the newer engine

-After all this: Took the cilinder out: Saw rings in good shape, cilinder with a few deposits of carbon and piston with nice build up of carbon at the top but saw that it was very brown on the sides (don´t know if this was normal)


I have used 50cc / litter all the time. But i like to go fast. so the engine was hardly used. I am concerned of this because there not was any noise that could aware me of an engine failure.

Pics:
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Sorry if the photos are not so well. tooked with a cellphone

At this moment I count with new cylinder/gaskets/piston/rings in order to restore it's compression but I did't found any clue with my little knowledge about 2 stroke motors...
 
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I have a very similar situation. I have a little over 600 miles on my engine and also your engine symptoms sound the same as mine.

On mine , I have grown tired of trouble shooting it and am just going to purchase another kit to replace the worn out one. My guess is these engines can only last so long and as they are reasonably priced there is more reason to replace them than to continue on trying to find the problem.

Sense you have 1300 miles on yours and I have 600 miles on mine, what more can you expect from a 2 stroke engine ?
 
I had a compression issue on the first of 5 engines I have bought. That issue was caused by something besides the engine itself, I won't go into that now. But, I don't care how fast you peddle you just won't get it started. With that said, I towed my son on it with my bike. Sure enough it would start but as soon as he stopped the engine would quit, unless that was that he held almost full throttle. These engines don't have that much of a compression ratio to start with, so a small percentage drop will make more of a difference then you could imagine.
To me, by the looks of your photos you have a compression problem, and you can't usually tell by just looking at a cylinder/rings/piston if there is a problem until the problem is so far gone it's very obvious. How do you really tell if ring tension is gone...not by looking by the average person.
 
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That sounds logical to me.
Now I´m being realized that not all engines are being manufactured with same materials, as far as could see on this forum the engines that for example someones bought from grubee engines are more durable than theese chinese "generic" ones.
 
You could always try removing the gaskets if you have enough clearance (this will up the compression). That's if your willing to throw in the towel anway. Try contacting the vendor, new rings are cheap!
 
HI, you have run it a bit hot, ie: the glazed bore, you really should get a new piston, small end bearings, gudgeon pin and rings. The soot on the piston is blow down. the localized brown coloration could be the start bearing failure. You can get away with a hone and new rings. But that piston is not 100%. The bottom ring i can see the locating tab? is it sticking at all? i should not be able to see one end of the ring? the only time i ever see them, is if the ring is stuck.

Because there are so many manufacturing differences in the motors it would be a good idea to get a complete piston and cylinder or get a micrometer, measure your piston and get that exact size off a supplier. The whole she-bang is on ebay for about $30 plus postage. so its not too expensive to get going again.

All is not lost either. If you want to go fast, While you have it apart now is a perfect time to remove any casting slags from your transfer passages etc. Get quality bearings that are within spec, and balance it if possible

If your running a bit hot you can adjust / retard your timing a few degrees with your magneto stator coil. Move the coil end downwards /anticlockwise to retard the ignition timing, raise your carburetor needle a notch or 2, or get a bigger jet, more fuel will cool it down considerably. A higher octane fuel will also help. and check for any air leaks..

Or buy a new motor? perhaps it would work out cheaper and you would have some spare parts left over
 
That sounds logical to me.
Now I´m being realized that not all engines are being manufactured with same materials, as far as could see on this forum the engines that for example someones bought from grubee engines are more durable than theese chinese "generic" ones.

Wasn't sure what engine to get at first...bought the cheapest one I could find, I switched suppliers on the rest due to supplier warranty (dead coil within 3 days). I'm happy with all of them.

I won't buy ANYTHING from "luckyearlybird" ever, ever...I'll do without first.
 
you mentioned theres no "suck" when you cover the inlet manifold...

two strokes have TWO compression cycles... crankcase and combustion chamber.

me thinks you maaaaaay have a cruddy crank seal... rubber seals. on the shaft itself.

this "dying off after half hour" seems normal... mines always doing it...day, time, temp, humidity...grrr!

mine also has 4500km on it before it died, turned out to be the top ring disintergrated, bottom ring stuck tight. ports smashed, bore gouged... it was running enough to get me home like that though... and it was cus of me fiddling... :)

in other words...youd actually be AMAZED at how bad a cylinder can get and still run...

meh. buy a new one :) cheap n easy :)
 
I've got to agree w/ Bob upon further inspection. That's a sleeved cyclinder! Might run w/new rings and stuff for a while, but not for life expected out of new motor for sure!

Sorry I didn't notice earlier, Good eye for an old Guy!
 
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