Blown 80cc HT engine

Discussion in '2-Stroke Engines' started by Frankfort MB's, Apr 16, 2016.

  1. Frankfort MB's

    Frankfort MB's Well-Known Member

    i was riding my ported 80cc and over a 1-2 mile range it tended to foul the plug out... Let bike sit a little then tried again and the bike was locked up and would not come loose... Just wanted to know what problem could be even though I'm just going to buy a new kit
     

  2. crassius

    crassius Well-Known Member

    could be that plug didn't foul, but your piston seized
     
  3. Frankfort MB's

    Frankfort MB's Well-Known Member

    I know that it did foul because the spark plug was covered in oil, the piston wasnt seized then it just didn't run right... My thoughts are that the motor got to hot from riding with slower traffic
     
  4. crassius

    crassius Well-Known Member

    then a new plug should get it running
     
  5. Frankfort MB's

    Frankfort MB's Well-Known Member

    The motor is locked up... Took head off and the piston won't even move... Tried 2stroke oil to lube it up no dice, I'll yank it apart in the next few days to get the real truth behind the mystery ;)
     
  6. Timbone

    Timbone Active Member

    I am working on my third engine. None of the three ever seized. Since compression is so low, I would posit that seizure would be caused by 1) lack of oil or 2) block warp caused by excessive heat/ very high mileage.
     
  7. Frankfort MB's

    Frankfort MB's Well-Known Member

    I was running 30-1 oil with synthetic echo chainsaw oil and the engine has about 150 miles.... I was actually at a really big car show in Tennessee and the traffic only goes like 15mph and I can cruise a little faster riding on the side of the road, people love these things down there so of course I have to do the requested burnout or revving lol
     
  8. Timbone

    Timbone Active Member

    15 mph on a 44T sproket would be a decent RPM at low load. Maybe hours of this would be a problem.

    If I wanted to seize the engine I would run high RPM with low oil and lean mixture. Or maybe WOT on a steep hill i.e. high load. I think 30:1 mix is good.

    Let us know what you find.
     
  9. Frankfort MB's

    Frankfort MB's Well-Known Member

    I would get up to about 30-35 just to race a couple guys on stretched mopeds with slicks after all what are these motors for? ;)
     
  10. Frankfort MB's

    Frankfort MB's Well-Known Member

    Opened up the motor tonight and saw a couple fragments of what looked like a piston ring (I accidentally broke 2 sets putting the cylinder on) took those out then motor freed up so I'm going to order my head gasket then I'm gonna test her out... Should have lightened my piston when I had it out :) another day....
     
  11. crassius

    crassius Well-Known Member

    make sure piston is right way around, as that is common cause for breaking rings - I doubt I'd ever run that motor again unless I were totally sure I'd found all pieces of those rings
     
  12. Frankfort MB's

    Frankfort MB's Well-Known Member

    In the middle picture if you look to the far back beside the crank you can see a fragment melted to bottom end
     

    Attached Files:

  13. sbest

    sbest Active Member

    Ring doesn't appear broken, pin looks fine. I see the bit of junk in the crank. Where did it come from?
    This engine looks pretty good, rescuable. Pull her apart and clean her out?

    Lots of blowby on the piston and rings don't look seated.

    Steve
     
  14. Frankfort MB's

    Frankfort MB's Well-Known Member

    Yeah I know, I went through 2 sets of rings the first time I took the motor apart and a peice of one of the rings must have fell down in the bottom end, for the blowby I just switched the rings around and double checked how they were seated on the piston, the engine should look good it's only got 150 miles on it lol
     
  15. crassius

    crassius Well-Known Member

    your fingers in pic are coated with metal debris - no telling what's in bearings - clean everything REALLY well
     
  16. Frankfort MB's

    Frankfort MB's Well-Known Member

    I made sure I shouldn't have to take motor apart again.... Soaked everything in 2 stroke oil for safety
     
  17. crassius

    crassius Well-Known Member

    before or after washing out cases really well?
     
  18. Frankfort MB's

    Frankfort MB's Well-Known Member

    After, most of the peices come out after a very firm shaking, double checked everything afterwards though
     
  19. butre

    butre Well-Known Member

    looking at that picture it appears a stud has punctured the case. that's meant to be a blind hole. tear it down completely and get that metal debris out, then jb-weld the stud in place making sure it's an airtight seal.
     
  20. Frankfort MB's

    Frankfort MB's Well-Known Member

    It was a ring that I broke and it ended up in the bottom end, waiting on head gasket to put back together
     
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