i have a 400 scrammy 2x4 2 stroke, went riding this weekend at dunes, lost all compression, toook engine apart and found a hole the size of pencil thickness right square in the middle of the piston top. anyone had this problem? im thinking that the oil injection pump failure. does anyone have advise? THANKS FOR THE HELP!


yours truely,"the broken one"[img]i/expressions/face-icon-small-sad.gif[/img][img]i/expressions/face-icon-small-disgusted.gif[/img][img]i/expressions/face-icon-small-happy.gif[/img][img]i/expressions/face-icon-small-mad.gif[/img][img]i/expressions/face-icon-small-shocked.gif[/img][img]i/expressions/face-icon-small-tongue.gif[/img][img]i/expressions/face-icon-small-cool.gif[/img][img]i/expressions/face-icon-small-frown.gif[/img][img]i/expressions/face-icon-small-cool.gif[/img][img]i/expressions/face-icon-small-tongue.gif[/img]

 

Thats what it sounds like. I did the same thing but I was running to lean. That sucks Man. But like I said be there done that.

 

Thats not my vote. 4 strokes run fine with no oil going into the combustion chamber. The only thing the oil does in a 2 stroke is lube the bottom end and keep the rings from sticking to the bore.
The only thing that can cause this in MHO is #1 Detonation or #2 lean or #3 a combo of #1 & #2. ( O.......one more; #4; if the timing gets jacked to the moon this will cause #1)

 

what would cause detonation, as ive been told no oil to the engine and you end up running lean causing to much heat and no lube. i also had my polaris watercraft loose the 3rd cylinder in similar fashion due to no oil. the scramy is a 01' if it makes any diff.

 

No oil and you would have heavy scuffing of the cyl walls. What color is your plug? Dark gray? Thats what color my plug was when I leaned out and melted the top of my piston.

 

spark plug was a greyish white, i heard a real tinny sound from engine just befoore it died, it still turns over, just really fast, no compression. i just took it apart tonight. im curious if capping of oil injection and just running premix would be the better route?thanks

 

There are many things that can cause detonation if you are close to detonation in the beggining.
Bad or old gas
Lean (something go in a jet and leaned it up?)
Timing (Key sheared off and advanced?? Something came loose and cranked the timing up??)
High air temp
Big time load on the motor with some or all of the above. (Sand riding???)

Which one is it??? I just can't say, but I agree with EAB. I have never seen a 2 stroke run dry of oil without scuffing the piston and bore all to hell. Or just plain weld the piston to the bore. If the bore looks OK it's not an oiling issue.

O.........and that tinny sound that you heard, that would be a good description of a 2 stroke detonating.
Let us know what you find out.

 

the tinny sound i heard ive been hearing for about the last three times riding. ive been using 92 octane fuel and it doesnt sit around for any amount of time. what does a greyish white spark plug mean?

 

the piston head seems to be rather clean, almost like it has been scorched, a small amount of edge on piston top has broken away too. the ony mods i have done to it are, k&n filter, hpd silencer, violet color primary spring, the main jet is stock, neddle setting is i believe second clip from top. i dont know if anything ive described would be a factor in why it blew. i wasnt hoggin the engine. but it seems like it hasnt been using very much oil from the oil tank.

 

if piston wash are clean on top of piston,that mean you were too lean,
,too rich,all top piston is black,perfect the piston must be black
with some fade to white spot in the middle.