Engine Trouble blown engine..am I at a loss?

[MrHungwell94]

Just got my bike running today (it was running last year, ran into electrical problems, decided to store it for the winter) and I took it for maybe a 30 minute ride when all of a sudden I lost power and the engine died, and had no compression...took it home, took it apart, noticed the piston had some scoring and the jug looked pretty bad on the inside like maybe it was a bad mold and the piston was chipping away at the ports. I still didn't think it seemed bad enough for my engine to be acting this way though.
So anyway I have this parts motor (all the engine mounts are completely stripped, failed attempt at retapping them, but other than that the motor was running fine for about 3 years) that I took the piston, jug, head, and bottom gasket from and transfered over to the one I blew hoping this would solve my pronlem. It did not. I still get no compression, the motor turns over simply by walking with the bike with no added weight. It will fire but wont run. I don't know where else I could possibly be losing the pressure from...does this sound fixable? Or do I buy a new engine?

 

[crassius]

it would seem that even if cases had a hole right thru, that the top would still get compression

this kind of 'can't happen' thing usually can be found by a more careful look at all the parts - like maybe a woodruff key failed or something similar

 

[MrHungwell94]

it would seem that even if cases had a hole right thru, that the top would still get compression

this kind of 'can't happen' thing usually can be found by a more careful look at all the parts - like maybe a woodruff key failed or something similar

I don't know much about the inner workings of the crankcase... Today I was turning the motor by spinning the wheel by hand listening for a possible leak when all of a sudden I felt it regain normal compression for a minute, long enough for me to try turning it over by giving the wheel a good hard spin about 3 times before I felt it loosen back up to having very little compression...I'm thinking about buying a top end rebuild kit which includes piston, rings, jug, head, and gaskets, but before I do that Im wondering if anyone agrees with me on doing this or if anyone advises against it...

 

[butre]

I'm advising against it. I'm 100% sure it's a sheared woodruff key. are you sure it's no compression and not simply no resistance?

 

[MrHungwell94]

It feels like it has some compression just very little but I can't find any leaks..not 100% sure what you mean by resistance but I believe you mean it not moving the gears making it easy to go up and down? When I move the piston up and down the drive sprocket turns and vise versa, wouldn't a sheered woodruff key prevent this? Sorry for my lack of knowledge here

 

[crassius]

it could be sheared such that it still turns when no resistance is present - if you take head off & look, it may seem OK, but with head on & muffler off, you might see the piston stop

either way, compression doesn't come & go like you describe - careful looking should spot the problem

after 2 top ends, I'd not expect a third to help

 

[MrHungwell94]

Wasn't the woodruff key. Upon closer inspection the original motor went because the jug and piston were both sheered to hell, after putting the replacement piston and jug on from my parts motor there was an air leak. Get this - my head gasket was on upside down. Flipped it around and it fired right up. Not before ordering a new motor though... Oh well at least when the new one comes, it'll be good insurance

 

[butre]

head gaskets for these things don't have an upside down

 

[MrHungwell94]

It is shaped so that one side is cupped and the other side is lipped, so clearly it only goes one way. I had my head tightened down properly and I could hear the air getting sucked in by the gasket when I put my ear near it. Flipped it around and problem solved. Sure if the gasket was flat it wouldn't matter which way it went. But in my case the gasket only fit one way, possibly from being worn into that shape

 

[crassius]

that lip as you call it is pressed into it by the compression ring of the head - when reusing one, it is best to turn it over to get a fresh bite