blew spark plug out!

crabdance

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Well... I have been trying to trouble shoot why my bike has lost power since I put another carburetor on it and one thing I tried yesterday was to get a new plug. Since the NAPA store couldn't find a replacement plug I looked on the board and found a recommendation for a replacement.

This morning when I took the bike out for a ride, it went about 300 feet and then the spark plug blew out the top of the motor! Needless to say, I'm not overjoyed at the moment.

My question is this. What is the likely damage? Am I going to need a new engine? New Head?..... I could go on but I don't know enough about these little engines.

I would really appreciate any help with this. This little bike has become my friend and I really like riding it everyday. It will be sad if I can't ride.

cd
 

arceeguy

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You can buy a heli-coil thread insert kit to fix the head, but I wonder what caused the engine to puke the plug in the first place?

Usually, when a small engine spits out a plug that wasn't cross threaded, it is because the plug wasn't torqued down tight enough. The plug cannot dissipate heat to the cylinder head, and gets so hot it melts the aluminum and shoots out of the head. A lean mixture will cause combustion temperatures to skyrocket too, but usually the piston will burn or seize before anything else. Since you only drove the bike a few hundred feet, there really wasn't enough time for the above scenarios to happen. Maybe the new plug had slightly different threads and didn't fit quite right?

I would try and buy a used head from a member here, since the heli-coil kit with tap, inserts and required tools is probably more expensive.
 

hill climber

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try sraewing it back in it may have just vibrated out if not remove the head and take it to a local machine shop/auto repair facility. spark plug threads are ofter mift and repair is simple
 

crabdance

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Thank you

I have to say thanks to both of you and You are both right about the problem I had. The plug was not in there tight enough and vibrated loose and just shot out. I just tried to put the plug in and road around the block like nothing ever happened.

Forgive me for being such a dummy. I always think the worst. I am just SO relieved that it was only that wrong with it and not something else. So my bike is running and happy and I'm happy once again too.

Oh, and I also put the plug in tighter this time. Not TOO tight but enough to hold it in there.

thanks for being there guys,
cd
 

srdavo

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this might be the cause of your lost power......you were prolly losing compression around the sparkplug hole.

I agree with arceeguy.... someone will have an extra head & gasket lying around.
 
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arceeguy

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Glad to hear it wasn't a major problem!

I assumed that the threads were stripped out when the plug came out, but you know what they say about assuming anything!
 

crabdance

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Glad to hear it wasn't a major problem!

I assumed that the threads were stripped out when the plug came out, but you know what they say about assuming anything!

Believe it or not I could screw the spark plug right back in. There is a small place at the very top where the thread is out a little but the plug will still go back in.

I'm just happy that it wasn't anything worse. I went to my neighbors house and asked for a shot of whiskey (didn't really drink one). He said "wow" what's up? I told him about it and he's the one who said it might just go right back in.

I'm just SOOOOOOOOO happy that everything is ok and nothing serious happened. I was bummed there for a while.
 

Skyliner70cc

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Don't use antiseize. it isn't required and could put you at risk of stripping the thread if you do use it. Antiseize use requires about 50% less torque to be applied or you overstress the threads and risk stripping them. Lots of folks dont' know this.
 
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