2nd tank of gas, bike wont start

Does the pison have any scrapes and gouges anywhere on it? Are any of the rings broken? Do you seen any gouges in the cylinder? How about where the piston hooks on to the connecting rod? Does everyone look ok? How is the wrist pin and the wrist pin baring? If you found "debris" in your engine that sounds like a problem. Rubber sand? Whatever that is clean it all out. Also, did you lose a seal or something? Take the side plates off and have a look at them. Tell me, when you try to start it can you feel compression? I mean, when you release the clutch lever does it turn over and do you have compression?
 
Piston looks ok. It looks like there is some scoring on the cylinder walls. The attached image shows the horizontal scoring. Its a little hard to see but there is also a vertical gap in the scoring of the cylinder wall at 12:00.

Again sorry for the lack of any sort of knowledge or experience on my part. I'm not sure about the compression. When I release the clutch there is a good 3 second pause before anything feels any different. When the choke is on it sounds like nothing is going on, choke off the engine sounds like its trying to do something. You can hear the cylinder going up and down throughout.
 

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Alright, pictures are good. Posting them really helps. I don't see anything bad happening in that picture, although I can't see the entire inside of the cylinder, if there is a large vertical gouge that would be a problem but I don't see that. It don't look like a problem. If you don't see anything bad on the piston the top end should be ok. I think you can put that back together. Don't forget to line the rings up with the pins and squeeze the rings together to get the cylinder back on, you don't want to break the rings putting it back on. Also, make sure the base gasket is good before you put the cylinder on.

However, when you release the clutch lever (and engage the motor) the compression should happen instantaneously, it shouldn't take 3 seconds! Are you sure the clutch is working right? When you pull in the clutch lever the back wheel should spin freely and the instant you release it it should immediately be more difficult to move because of the compression. If this is not happening you probably just need to adjust the clutch cable or clutch itself.

Also, tell me more about this "debris" you found? How much was there? Where was it? Was it particles of rubber? You should remove the magno case plate and check the rubber seals!

brnot
 
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I'll second the suggestion to check that the clutch is really engaging. I've only built one bike and I couldn't get it started at first. I thought the clutch was engaging, but it turned out to be that it was slipping so the engine wasn't turning over. Tightened the clutch and started right up.
 
New rings, New CDI, New Magneto.....still nothing.
When I changed out the magneto, I discovered it to be covered with fuel. A quick search of other threads leads me to believe the crankcase seal is bad. In reading those other threads it sounds like ordering the right seal online is a roll of the dice. Any suggestions on where i might find the correct seal?

Other thoughts on where that fuel might be leaking from?
 
search on ebay for "80cc crank bearing seals" they're pretty cheap, but on a new motor you may see that for some reason it is just crooked in the seat - usually using the flat side of a big socket, one can tap it back in straight

while looking there, pry up on that end of the crankshaft to see if bearing is bad and letting crank move up/down which can also cause a good seal to leak
 
In the ongoing saga of this bike....I was in the process of replacing the crank bearing seals when I discovered some of the clutch pads were shredded.I assuming the debris I found was from the clutch pads.
Seems easy enough to replace but my question is why did the shred in the first place. Would really rather not go through this again

Pic of said clutch pads is attached.
 

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yeah, they're OK - one might want to trim them a bit to fit the slots nicely as they work much better when the force can be applied evenly thru to the back plate - the factory never trims them for you
 
How did the seals look? Were they worn or chewed up at all? When you opened the magno plate cover did you find oil in there? If the crank is bent the new seals won't last long, does it wobble?
 
kayosdad said:
seals were not chewed up, there was oil in the magnet case.
Sorry, does what wobble?
Click to expand...

Okay, if there is oil in the case then the seal is definitely leaking and needs to be fixed. It's good that they are not chewed up, if they were it could mean that the crank is bent. If the magnet wobbles when it spins it could indicate a bent crank. A bent crank will just tear up your seals and although the crank can be replaced I would just get a new bottom end at that point. However, if they are not all chewed up it sounds like the seal on the magnet side is just leaking. You can try to reseal it if it is still in good shape or you can replace them for only $7. There is a seal on the magnet side and one for the clutch side but the one on the clutch side might not be leaking.

http://www.ebay.com/itm/301921571372?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT
 
oil in that case can sometimes be coming thru the 4 holes drilled for mounting the armature of the magneto if it doesn't sit flush with the case - I sometimes add 4 soft aluminum washers there to fix that
 
How about the choke?

On the NT carb, just remove the choke plate with the little bolt.
On the CNS carb with a cabled choke, just go buy an NT carb.
 
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The bike is up and running. It appears that was indeed the crank case seal. Replace the one on the magnet side and it fired right up.

Thanks so much to everyone for their input.

Is there anything I can do to keep that from happening again?
 
if it isn't caused by a defect in the seal or poor installation, then the most common reason for failure is leaving petcock on so that bottom of motor fills with fuel - first kick can then blow it out
 
kayosdad said:
The bike is up and running. It appears that was indeed the crank case seal. Replace the one on the magnet side and it fired right up.

Thanks so much to everyone for their input.

Is there anything I can do to keep that from happening again?
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Right on! Anytime you see oil inside the magnet or clutch cases it usually indicates a leaking seal. After you ride it for a little while, open the magnet case to make sure the seal is still holding good. Also, Crassius is right, always close the petcock after riding. Keep riding and breaking it in!!
brnot
 
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