Engine Trouble compression problem?

[Soundquist]

hi, i'm new to the forum. my bike was running fine until i took it apart to replace a gasket i had seen hanging from the bottom as a result of a loose case screw. during reassembly, i broke about a cm. off of a piston ring and foolishly tried to run the engine with the damaged ring in place. it seized up, the broken edge catching on one of the openings in the cylinder wall.i was able to free the cylinder from the piston after much horsing and cussing, to discover a small, L-shaped gouge on the wall of the cylinder. i filed and sanded it out pretty well and replaced the broken ring and put it all back together. the bike won't run.
it turns over fine and i checked the spark by turning the wheel and it works fine, so, my question is how sensitive are these chinese kits when it comes to that piston? the compression seems okay, you can feel it in the spark-plug hole, and when plugged the bike seems about as hard to roll as it ever did. okay, a little bit easier. could a tiny air-leak between the piston and the cylinder be the cause of my bike not starting?
-carl

 

[Deleted member 12676]

I'd guess that as long as the rolling starting compression feels the same then that is not the problem. But compression can be lost at the crank seals and at the intake, between the carb and the engine.
check for gas and spark.

 

[BigBlue]

Take out the plug and put a small amount of gas in the spark plug hole. Put the plug back in and try starting.

Chris
AKA: BigBlue

 

[Soundquist]

Thanks for the feedback. Checked spark again this morning still looks good. Fuel bowl fills fine and tried a little gas in the spark plug hole a few times, no luck. I live on a hill so starting has never been a problem. Any ideas?

 

[Deleted member 12676]

spark plug should be wet after trying to start it.
it's easy to miss an air leak. do you know how to test for crank seal air leaks?
yeah you have spark but you screw the timing all up by installing the magneto opposite of how it should be. a very easy mistake.

 

[BigBlue]

spark plug should be wet after trying to start it.
it's easy to miss an air leak. do you know how to test for crank seal air leaks?
yeah you have spark but you screw the timing all up by installing the magneto opposite of how it should be. a very easy mistake.

Good point. Your timing might be messed up. If you removed the magneto, you may have installed it backwards or incorrectly. Here's some info. from Grubee on how to install it correctly:
http://www.grubeeinc.com/USA/Magneto Mystery.html

Good Luck,

Chris
AKA: BigBlue

 

[Soundquist]

Spark plug is wet. Not sure which is the crank seal, or how to check for leaks. You mean the magnet is backwards? I wondered about that.

 

[Soundquist]

Wow. Flipped the magnet and there she goes. Thanks guys. Had to ride the caveman bike to work for 2 weeks. Jeez. That idea actually occurred to me but i judged by the markings on the magnet that i had it right. Thanks again!

 

[Chris zoom zoom]

Why do I lose compression wail riding and then it comes right back. Then It find the gone and right back I have check carp spark plug replace top head gasket and still having the same issue

 

[Deleted member 12676]

the head is warping with the high heat at the top RPM. When it warps, it contorts and allows blowby.
http://www.dragonfly75.com/motorbike/headtemp.html