Motor exploded in smoke?

Discussion in '2-Stroke Engines' started by James Owens, Oct 20, 2017.

  1. James Owens

    James Owens New Member

    I've had my bike up and motorized for a few months now and have probably around 400 or so miles on it. While I was getting ready to ride it today, I made it about a block away from my house and the stock muffler broke off of its pipe. I figured no big deal and picked it up and dropped it back off at my house and decides to ride to my destination without it because I was in a hurry. I made it about a block away without the muffler and the motor started to die so I pulled over to check it out, and while idling it started making loud popping sounds. During each of these pops smoke was errupting from every possible part of the motor. It was coming out around the head (even though I know the head had been properly tightened), around the seals of the crank case, from under the magneto cover (somehow?), even from out of the air filter on the carb. I pulled it back home and noticed there is now a small hole in the crank case cover. I have no idea what caused this, and my bike won't really run now (it will turn over and sort of run but wants to die really badly (presumably from lack of compression). What in the world happened? Is there any way I can fix this without just buying a new Motor? It's basically my main means of transportation so help would be greatly appreciated!

    Will post pictures when I get home

  2. crassius

    crassius Well-Known Member

    hard to tell at a distance, but sounds like too much vibration - check for looseness at seals and gaskets (including case bolts)

    periodic checks like that are an easy way to spot other problems, even when everything is already tight

    the hole in some cover (I'm thinking clutch cover) usually is small bevel gear bolt came loose or flower nut was badly adjusted
  3. gary55

    gary55 Well-Known Member

    Start taking it apart. Side covers and obvious problems first. Smoke in the crank case usually means ring/cylinder problems.
  4. Frankenstein

    Frankenstein Well-Known Member

    Magneto might be rubbing and slipping out of place, muffler issues can make it run hot if air is seeping back in..

    I would buy another engine yours sounds like it is toast..
  5. gary55

    gary55 Well-Known Member

    Toast big time toast.
  6. James Owens

    James Owens New Member

    I usually give the bike a full once over to make sure everything once every few days, but didn't today. The reason the muffler broke off was because one of the studs had apparently came loose. I looked down seconds before it flew off to notice it swinging wildly back and forth. I'm just curious as to why riding it for all of maybe 2 blocks total without the muffler caused this complete failure. I attempted to patch the hole I was talking about using some JB weld, but I don't want to run it to test it without a muffler. I also tried to epoxy the muffler back together with JB steel stick and JB weld but it didn't hold, so I'm planning to take it to a welder as soon as possible. I'm at a loss as to why things failed so spectacularly so suddenly. Up until now the bike has ran flawlessly.

    This is the hole I was talking about 20171020_154341.jpg


    And here's the broken muffler

    I intend to disassemble tomorrow and see what's up inside

    I appreciate the replies! Reading on this forum has been a huge help to me in the past, but this mis my first actual time posting
  7. gary55

    gary55 Well-Known Member

    After seeing this maybe the motor isn't toast. Might get away with tightening the screw that backed out and welding the muffler back on. Make sure the woodruff key is still in the gear behind the screw. Still wonder where all the smoke was coming from. Should probably pull the head and have a look.
  8. crassius

    crassius Well-Known Member

    yep, that's the bolt for small bevel gear - should be fixable
  9. KCvale

    KCvale Motorized Bicycle Vendor

    You could have just bought a new pipe and had it in hand than what you are spending on JB band-aides and now taking it to a welder?

    If you can salvage the engine get a new pipe, but why waste all the time and parts cost trying to fix your engine which will always be 'broken', just by a new one and use the old engine for parts.
  10. James Owens

    James Owens New Member

    That's a huge relief to hear, thanks guys!

    I already had the epoxy laying around so I figured I'd give it a try. I'm planning to get a quote in the muffler and if it's more than $10 I'll probably just get a new one. I'll probably be able to get the weld done for pretty cheap because the welder is a family friend.

    Unfortunately I'm a student on a tight budget and I can't afford the $80-$100 for a new kit at the moment. It really sucks because the bike is also my main means of transportation to and from class
  11. James Owens

    James Owens New Member

    I pulled the clutch cover off and found that the big machine screw / bolt that holds the small bevel gear in place had come loose and that was what ate a hole in the cover. I went to the hardware store and got an m8 bolt and ground it down with a dremel until it wad the same dimensions as the original and popped that in there.

    I also ended up buying a $3 lawnmower muffler and I ground down the threads on it until it would fit snuggly into my muffler pipe.

    I also ended up changing out the magneto and cdi because I had new ones on hand any way (I had ordered then because I suspected I had moisture buildup in my cdi chamber area) and put in a new spark plug.

    I also filled the entire frame of the bike with spray foam insulation to reduce vibration.

    I haven't yet had the chance to take off the head and big and see how the cylinder is looking, but I plan to do that this evening (and if it looks good, do a port and polish job on it).

    After taking it on a test ride after the aforementioned adjustments, the bike seems to be doing be doing better than ever

    Here's a picture of the screwed up screw
  12. crassius

    crassius Well-Known Member

    glad it worked out - might be time to stop fixing and start enjoying