what are the long term effects of an air leak?

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mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
the engine has not seized. just boged down. it stills starts right up. and my experience is taking this thing apart yesterday... thats about it. i didnt have a gear puller so i couldnt pull the bottom end apart. but i was able to pull the head cylinder and piston, apart. the only thing i noticed was it looked like something was rubbing the piston by the exust port as the piston had some slight indentation by the exhaust manifold.

this leak started with a cracked carb body the i repaired....(i Thought... HA!)

Do as you will on this, but if the piston is scored and the cylinder is scored "Scratched" pretty good in any area around any port you are running a risk of a having a ring break if scored area is bad enough, this will of coarse be a major failure which would require you to completely tear down your engine and could destroy your lower end as well as the top.

So running that engine after knowing there is a problem is a real roll of the dice now, but you will know something pretty soon after getting the new carb. installed. just be easy with it and see how it does is my advice, good luck I hope it runs out for ya without needing a rebuild.....!

brnot
 

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
And yes these little china girls do shake rattle and roll, I have 3 of these engines on bikes they all do the rattle knocking bit, the fit of the internal parts of these engines are not very precision so they do make a little racket......that is normal from what I have seen personally.
 

Maxvision

New Member
Jun 13, 2009
551
1
0
San Diego, CA
When you pulled your cylinder, did you check your rings? A dent in the piston means something got in your cylinder. If you cracked a ring (or rings) you might not be getting the compression you should be.

Another good idea is to get some calipers and measure the cylinder width and your piston width. I got an engine once that had the wrong size piston in it. Was ALOT of rattle noise from the piston slapping around inside the cylinder. Remember that the piston is going to be a bit smaller than you cylinder. I've attached a picture (courtesy of Spooky Tooth) that gives you piston diameters for different cylinders.

engine-ID.jpg
 

pechroc1

New Member
Sep 4, 2010
35
0
0
flushing,ny
the markings on the piston are not hard scores more like a light indentation... like whatever was in there didnt have hard edges...the only reason i noticed them is because i felt it. its not visible to the eye. but i checked and checked again and the cylinder body has no indent or scratch at all. i did a little polish and she real pretty. and the rings are in good condition. whatever was in there never mad it as high as the rings. im going to order a new piston, pin and rings anyway.

as for the rattling... it wasnt there before. so its just irks me a little. the carb was delivered but im away this weekend so ill be running her sunday night and ill key you guys in.

thanks again!
 
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pechroc1

New Member
Sep 4, 2010
35
0
0
flushing,ny
so i threw all that... turns out everything was fine with the new carb. she was riding very nicely...EXCEPT... in reusing the g pin it failed ,broke, and destroyed the piston and cylinder after a ride around the neighborhood. so back to rebuilding the top end... plus i need to get that gear puller to make sure i find the piece of the g clip if its still in the bottom end... GRRR. ill be posting if i need any help thanks guys. ttys

Do as you will on this, but if the piston is scored and the cylinder is scored "Scratched" pretty good in any area around any port you are running a risk of a having a ring break if scored area is bad enough, this will of coarse be a major failure which would require you to completely tear down your engine and could destroy your lower end as well as the top.

So running that engine after knowing there is a problem is a real roll of the dice now, but you will know something pretty soon after getting the new carb. installed. just be easy with it and see how it does is my advice, good luck I hope it runs out for ya without needing a rebuild.....!

brnot
PS.thanks for the warning... and to any other newbies: its not worth reusing a part you can buy for $1. no matter how long you have to sit on you butt.!
 
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pechroc1

New Member
Sep 4, 2010
35
0
0
flushing,ny
found a complete topend replacement here...
KingsMotorBikes - 66cc/80cc Top End
good deal considering.

the good thing is if i need to do the bottom end too its still would only cost me 90.00(free shipping with this site) as compared to the complete engine on ebay is 85.00(70.00 + 15.00shipping)
 
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mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
you will have some slack on these engines between the rod and the crank journal, because of the roller bearings/pin bearings that are used, so hopefully you are still good in that area.
sorry to hear of the major failure, I was very afraid that is where that little engine of yours was headed based on what you had said you saw when pulling the jug in the begginning, if you order from Kings Ihope all goes well, I have not ordered from them myself but have heard several complaints about there service, I believe Kings and Bike Berry are the same outfit, that is a good deal on that top end kit if it comes with all the needed parts like new clips, piston rings, new wrist pin and new upper bearing.

I wish you the best on the rebuild and be careful when reinstalling the woodruf keys on the crank while putting the bottom case back together, they can be a little tricky, or at least mine were and I ended up just cutting new ones from small flat washers with my Dremel tool.
 

Maxvision

New Member
Jun 13, 2009
551
1
0
San Diego, CA
so i threw all that... turns out everything was fine with the new carb. she was riding very nicely...EXCEPT... in reusing the g pin it failed ,broke, and destroyed the piston and cylinder after a ride around the neighborhood...
Yes! ALWAYS double, even triple check that clip. I always put a flashlight on it just to make triple sure all of it is in the groove. (but then I don't see near as well as I used to!)