piece of cylinder wall broke off BGF china girl motor.

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tylerlough

New Member
May 28, 2008
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Mishawaka, IN
I've got about 2200 miles on a 66cc bushing wrist pin bearing engine from boygofast. Bought May 2008.
Riding down a slight hill at about 43 mph with 33 tooth sprocket, motor shuts off and won't restart so I pedal it home.
At home I find the rings are broke, piston has a deep gouge on the side of it and a piece of the cylinder wall below the transfer port is missing. The piece was ground up and scattered throughout the engine.

Is this cylinder usable with a new piston/rings?
Bottom end seems ok, rod bushing is a little worn.

This may be a good opportunity to upgrade to a puch jug and head if it's not too difficult. With a 33 tooth I can always use more power.reddd
 
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5446

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Jun 7, 2010
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on a bike
Re: piece of cylinder wall broke off BGF china girl.

I would buy one of his $72 motors with a piece of the cylinder wall ground up in your case it might be time to upgrade?
 
bairdco

bairdco

a guy who makes cool bikes
Aug 18, 2009
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living the dream in southern california
Re: piece of cylinder wall broke off BGF china girl.

you can use the cylinder for a paperweight, the piston makes a good ashtray, and the case would work as a doorstop.

i'd just buy a whole new motor. upgrading to the Puch top end after 2200 miles would probably just be a waste of money. the case's internals are probably sloppy, and adding more HP would just add more strain on it. it might be fine, but it's up to you whether you want to take the risk.
 
GearNut

GearNut

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Aug 19, 2009
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Re: piece of cylinder wall broke off BGF china girl.

Ouch! That is a gonner for sure! If you do inspect the bottom end you gotta insure that no fine debris particles have worked their way into the big end bearing.
It may feel acceptable right now but if there is any debris it won't be for long.
Out of curiosity, are both of the piston ring locating dowels still in place?
 
corgi1

corgi1

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Aug 13, 2009
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Re: piece of cylinder wall broke off BGF china girl.

that looks bad,I would get a new engine to use while you work on that one so you will have a bike to ride ,I would replace most everything in the crankcase and the whole upper end,that only leaves the clutch and sproket shaft and case useable if the case made it through the big piece punching a hole in it
 
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tylerlough

New Member
May 28, 2008
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Mishawaka, IN
Re: piece of cylinder wall broke off BGF china girl.

I'm thinking about just dropping in a new motor and selling the bike, then buy an old moped. Something with a good suspension. I don't really want something that I'll have to insure right now. I already have a car.
I'm not even sure I would be willing to part with the bike.
 
Goat Herder

Goat Herder

Gutter Rider
Apr 28, 2008
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Re: piece of cylinder wall broke off BGF china girl.

Bikeguy Joe said:
Totally rebuild-able!

;)
Click to expand...

Darn it Joe i was trying to get his brass bushing:)rotfl You can use that brass bushing again with the overhaul! Its way better than the roll cage bearings. Prolly has no wear on it at all!
 
corgi1

corgi1

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Aug 13, 2009
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Re: piece of cylinder wall broke off BGF china girl.

That new cylinder and piston really spruced up your bike,it really looks different lol
 
Goat Herder

Goat Herder

Gutter Rider
Apr 28, 2008
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N.M.
Re: piece of cylinder wall broke off BGF china girl.

That's one sweet up grade on cylinder and piston(^) looks like ya got a good deal. Low mileage on it too!
 
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tylerlough

New Member
May 28, 2008
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Mishawaka, IN
Re: piece of cylinder wall broke off BGF china girl.

I wanted the version with pedals but I guess I can't be too picky. A funny thing about this moped is the speedometer is in miles per hour but the odometer is in Kilometers.
It took me like 12 hours to finally get it running right, throttle cable was broke and carb was somewhat plugged. It's sucks trying to take out the carb, the frame is in the way, but at least it's a nice Dellorto SHA 14.12

The original owner bought it new in 97 but he died the next year, and it had not really been ridden since 98.
 
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tylerlough

New Member
May 28, 2008
109
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Mishawaka, IN
Re: piece of cylinder wall broke off BGF china girl.

I thought I had it run right but I went for a ride and it quit on me.

I think I know what the problem is. The oil in the tank looks like regular 4-cycle motor oil, it's a light tan color. All the two-stroke oil I've ever seen is dark in color and has solvent smell to it. The muffler was also had way too much oil in it for only 70miles.

Update, yep that was the problem.

I took off the cylinder head and it doesn't have a gasket, I think the guy forgot to put it back on.
 
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tylerlough

New Member
May 28, 2008
109
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Mishawaka, IN
Re: piece of cylinder wall broke off BGF china girl.

GearNut said:
It looks like it has a reed valve too, great for low end power and fuel economy!
Click to expand...
I think it does but I think the exhaust has a restricter to limit top speed.
It take off fast but doesn't go too fast, Perfect for off-roading, not too good for the streets. I think some taller gearing is needed.

The suspension works good for my 130lb self.
 
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tylerlough

New Member
May 28, 2008
109
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0
Mishawaka, IN
Re: piece of cylinder wall broke off BGF china girl.

corgi1 said:
Is it CVT or chain drive
Click to expand...
It's a two speed automatic that drives a 26t front sprocket and 22t rear. The rear axle has cams that allow you to adjust chain tension.
At about 15mph it shifts into 2nd gear. It's still being broke in 15 years later so I'm not sure what the top speed is yet. I've had it up to about 31mph on my GPS.
 
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