No Compression?

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No Compression Bike Won't Start!!

I just Replaced my Cylinder Body & piston & gaskets because they broke. but before it broke everything was Working fine. i had Compression & everything, but now when i try to start the bike the compression is very low & bike won't start. I am also able to roll the bike with the clutch out more free then before. i do hear little air coming from where the spark plug goes but my Cylinder head is not Cracked or damaged. what do u it could be why i cant get no Compression?
 
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2door

2door

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Sep 15, 2008
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We're assuming this is a Chinese 2 stroke engine. Always a good idea to tell us what you have when asking questions.

Is the spark plug tight? Did you replace the head gasket? Did you torque the head bolts to 120 to 140 inch pounds? Did you lap the cylinder head and check the gasket surface on the new cylinder? Did you use new piston rings?

These are just a few questions to give us something to work with.

What do you mean when you say the parts you replaced "broke"?

Tom
 
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Patchy

Patchy

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Did you check the tightness of the spark plug? Are all the bolts on the cylinder head tightened down all the way?

An easy way to check where the pressure leaks are coming from is to ride it as if you are going to start it and when you release the clutch (be sure its not going to start meow) put your hand around the head and feel for leaks. A wet hand helps too.

If you are feeling leaks on the head and tightening doesn't work, don't over do it, remove the head and take the gasket off. Try tightening it back up once more! If you still do not have compression you might need to sand down your head/ the top of your cylinder to make both surfaces completely flat and more likely to seal!

To do that tape some 100-200 grit sand paper on a piece of glass. You need something perfectly flat, and that's not the floor! Lightly wet the sand paper with soapy water and sand in a circular motion. Just know the more you sand the more you increase your compression too. Don't go overboard here! Oh ya, finish off with a fine grit like 300.

Now if none of that won't fix your compression... there might be evil a foot.
 
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its a 2 stroke & i replace the rings, piston, head & piston gaskets & body all new. i'll try to take the head gasket off & t& check the spark plug for air leakage.
 
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When i took the head gasket off & tight in up the head bolts i got more compression but tbe piston was hitting the celling. i also notice my first piston is smaller then the new one.
 
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crassius

crassius

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Sep 30, 2012
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if it is close to fitting, you may have a thinner base gasket this time & running 2 head gaskets may work, otherwise you got the wrong parts and need to measure them against the old parts
 
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yes i just switched back to my old piston & Now its working, but the new piston did not Work & had low Compression. can anyone Explain this? why when i switch back to old piston my bike Works but new piston doesn't
 
Greg58

Greg58

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Take a picture of the pistons side by side, a picture tells a thousand words. Post it here and someone will tell you what's the problem.
 
crassius

crassius

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you bought the wrong piston - note that the hole for the wrist pin is in different places on those two
 
Greg58

Greg58

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Piston bikes is where I got the link, they may have it in stock. Whoever you get it from tell them you need a type B and they will know what you need.
 
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