Wheel/chain wont turn with spark plug in. Please help!

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Kevbot365

New Member
Feb 27, 2013
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Southeast US
I am new here, but I've spent the last hour or so searching and reading through the forums here trying to figure out what's going on. I've managed to fix some of the issues on my bike thanks to you guys but I am still having one issue. My back wheel/chain will not turn with the spark plug in. I have bought a new spark plug and replaced it, but it's still happening. I can unscrew it almost all the way and it turns enough to start the motor but when I get moving down about 10 feet the spark plug pops out and kills the engine. I've looked through previous posts using the search function but the ones I'm finding don't seem to have this specific problem.

I am mechanically stupid. This is my first foray into anything with an engine, so please be kind (and explain it like I'm five). I can turn a wrench and am good with my hands, but I don't know the names for anything. I learn fast though so any help would be appreciated. Thanks in advance!
 
Bikeguy Joe

Bikeguy Joe

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Jan 8, 2008
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Well, you aren't that mechanically stupid, or you wouldn't have figured out you can unscrew the plug most of the way and have the piston not hit it...

Is the washer on the plug? Stock plug, or did you put something else in it?
Assuming you have a Chinese made engine kit?
 
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Kevbot365

New Member
Feb 27, 2013
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Southeast US
Bikeguy Joe said:
Well, you aren't that mechanically stupid, or you wouldn't have figured out you can unscrew the plug most of the way and have the piston not hit it...

Is the washer on the plug? Stock plug, or did you put something else in it?
Assuming you have a Chinese made engine kit?
Click to expand...

The washer is on the plug, I even added one from another plug. I bought a new plug with a smaller threaded area and it still dips too far in to avoid the piston.

Yes it's a chinese made kit. Bought the whole bike off craigslist (motor already installed) for a steal. I have gotten this thing going before, but I had to have the back wheel replaced with a thinner one because the chain was rubbing the tire (and it was bent anyway, which is why I think I got it at such a good price) so I KNOW this thing can run. When I first got it, my mom took a (small, don't worry) spill on it which is when I noticed the back wheel not cooperating so much. I took the housing off and saw what I later learned was the woodruff (? I think) pin was broken. Replaced that, thanks to searching here, today, because the clutch wasn't catching at all.
 
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Kevbot365

New Member
Feb 27, 2013
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Southeast US
It may have been hitting it before, but not as bad. Is there a chance that I could have screwed something up when I was taking the chain housing off?
 
Bikeguy Joe

Bikeguy Joe

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Not that would make the piston hit the plug. If it was hitting before, it would have closed the gap and killed the spark.
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
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If you didn't put in another plug, or forget to use the washer, then the only thing I can think of is that you somehow bent the **** out of your crank, and that's not easy to do.
 
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Kevbot365

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Feb 27, 2013
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Southeast US
I know it was locking up a bit when we first got it, but I assumed that was the wheel. Perhaps I am incorrect and it was something with the piston. I don't think I bent the crank, I wouldn't even know HOW to do that.
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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Try a shorter plug. Maybe the former owner put the wrong plug in it.

Any of these will work.

NGK B5HS, or B6HS
Champion L86C or L82C
Autolite 4093 or 425
Gap it at .024"-.028"
 
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Kevbot365

New Member
Feb 27, 2013
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Southeast US
I was just able to get it to start up by BARELY tightening the spark plug in, but I lost power pretty quickly, I'm assuming that's because of the plug not being secured properly?
 
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Kevbot365

New Member
Feb 27, 2013
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Southeast US
My socket wrench is stripped and I can't get anything else at that angle to get those bolts off, but I will buy another one tomorrow and get back with you.

Thank you for your help thus far!
 
crassius

crassius

Well-Known Member
Sep 30, 2012
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I don't know what a Champion CJ7Y looks like, but it is not on the cross ref for NGK B6HS.

Once you get your socket, you'll see it is easy to open the top & see what's going on.
 
Venice Motor Bikes

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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OP... Are you sure that the 'engine not turning' that you're feeling when you pedal isn't actually just the engines 'compression' & not the piston hitting the spark plug??? :/
 
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bigbutterbean

Active Member
Jan 31, 2011
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I'm wondering if he realizes what the proper starting procedure is. Kevbot, the lever on the handlebars should be pulled in and locked when the engine is off. The proper way to start the bike is to pedal up to a decent speed (5-10mph) and then release the lever on the handlebars. If you are trying to pedal with the lever released, that is why the engine won't turn over.
 
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