Motor exploded in smoke?

James Owens

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1:32 AM
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Oct 20, 2017
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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
 
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
 
Start taking it apart. Side covers and obvious problems first. Smoke in the crank case usually means ring/cylinder problems.
 
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

20171020_154346.jpg

And here's the broken muffler
20171020_002531.jpg

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

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


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.

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
 
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