New Cylinder Body wont start

Italian

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Jan 28, 2018
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so i messed up my original cylinder body in a way i wouldn't like to admit, so i bought a new one. it was a very simple swap but now my engine will crank but wont turn over. i know fuel and spark work because on the old cylinder it was fine, but i tested them again just to make sure. the only difference on this cylinder being that it is 2 mm shorter in stroke length, i dont know if the stroke length is mission critical but that is the only variable i didn't change. ive read that some spark plugs dont work under higher compression, ive ordered a new one already though.

Important note - i did get a single combustion once or twice while screwing with the choke when trying to start it, it was like a single puff and smoke came out of the carb side. everything was mounted in the right direction.

ill list here everything i tried

running it with the choke down for a while
refilling gas tank (more pressure?)
riding around the block with the clutch down to "clear out the engine"
making new carb gasket out of rubber
adjusting the air/fuel mix in every way
taking off exhaust
testing the sparkplug (works fine)
 

crassius

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Sep 30, 2012
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not sure what you mean here by 'stroke length', but if port mapping is much different, you might not even be opening the transfer ports
 

Italian

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Jan 28, 2018
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not sure what you mean here by 'stroke length', but if port mapping is much different, you might not even be opening the transfer ports
By stroke length i mean the vertical distance moved up and down by the piston. the ports are lose enough to where i cant tell the difference without measuring it, even inside the cylinder.

i deiced screw it and in gonna return the new cylinder. Better Question now, how good is JB weld at filling holes. since my original cylinder works i can replace it with that but, like i said, i snapped a mounting stud for the exhaust. the broken studs is still in there but i have a million other holes scattered around it from trying self tapping screws out of desperation. so if i used JB weld to fill the other holes and properly removed the broken stud instead of being lazy do you think that would be worth the money to try it. or do you need an ultra perfect seal to block out the noise.

This is my first bike and its starting to become a sort of money sink because of my lack of experience and unnatural ability to accidentally break parts so id rather spend the $25 and buy a new cylinder that is actually up to spec than waste it all trying to fix the kit i already have, or for that matter buy a new kit. i will say i learned alot about engines through out the process.
 

crassius

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Sep 30, 2012
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cylinder has no effect on how far piston moves - if your new one is taller than old, then you probably have very low compression

cylinder material is very weak, but jb-weld may be weaker

if you can get the old stud out, then for the clutch side stud you can drill deep enough to come out between the fins where there should be good metal to hold a helicoil with a bit longer stud, if it is mag side stud, then with cylinder off you can drill right into the channel for the head stud on that side which also gives you more good metal to plant a helicoil in
 

Italian

New Member
Jan 28, 2018
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perhaps i Should have specified, there not holes in the original cylinder, just arround the stud, nothing structural would need to be done with JB weld. It's not that it dosent function, it's just that my neighbours would call a noise complaint if i can't mount the muffler back haha.

Anyways I just wanted to get the opinion of a more experienced person. Idk if my repair method is too sketchy. The original stud is still in place and the original threads intact, so imma try and replace the stud. to be quite frank I would mind buying another cheap $80 kit from eBay (even though the shipping is more than a week) because I'm already too sunk in to this lol

Thanks for the reply, though I don't think this thread is gonna get very far though.
 

crassius

Well-Known Member
Sep 30, 2012
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yeah, I usually recommend a new motor instead of rebuilding - metal is so bad that it easily fatigues if at all damaged