Scrambler 400 2 Stroke Piston Questions

[justjohnthomas]

Tore into the engine of my 1999 Scrambler this weeked to figure out why it froze up last fall. Long story short is the piston skirt basically exploded. The cylinder dosen't have any scars or scratches on it, but the head has some pitting. First question is if the head is pitted is it reusable or should I try to find one on ebay? Second if the cylinder is smooth do I still need to have it bored out? Third is what brand of piston should I go with? (WSM, Weisco, Polaris, or Other). Fourth, anyone have any ideas of how to make sure I get all the metal out of the bottom end? This is the first 2 stroke I'm rebuilding and if it goes smoothly I'll be rebuilding my Mountain Max this summer also.

 

[mynameislance]

Pictures of cylinder and head would be helpful. Might not hurt though to do an oversized bore and get the matching piston; you should have one or two options for oversized bore.

As far as the piston, I personally have no problems with different brands of piston but would probably go with polaris or weisco.

Best bet for getting the metal out of the bottom end is to take it all apart and clean it good. Lots of people will say you can just rinse it out several times with gasoline (fill the crank, then turn the engine upside down) but there's no guarantee in that so if you don't get it all and the engine blows again, you won't be very happy. The time and cost it takes to tear apart the bottom end is cheaper than rebuilding the engine again, plus you might find something else that needs repaired.

Before changing everything though and just putting it back together, I would try to figure out what caused the piston to let go. Was it just worn out and fatigued or did something actually happen that caused the skirt to explode. I would guess if it was still on it's original top end that it was probably just fatigue.