I blew her up!

[page454]

I bought a 98 banshee about 2 weeks ago and 3 days later I blew it up. It is pretty much stock except for FMF pipes and mufflers, and k&n air filter with outerwear, as far as I know. The motor is .030 over right now. I was on a dirt road coming back from a friends house, and yeah I was running her pretty hard, but the engine seized up, which I later found to be a seized rod bearing on the left side. The piston on the same side doesn't look too good either, it starting melting and pieces of piston are melted into the head. The other side looks perfect, considering the engine was rebuilt this spring by the previous owner. The spark plug on this side, the electrode was pushed up into the plug, but both plugs are a chocolate brown color. So I tore the engine completely apart and the rod was seized to the crank, and pieces of the rod bearing are laying in the bottom of the case. I bought a used crank and rod assembly, new .060 wiseco pistons, rings, piston pins, clips, and needle bearings. Also a complete gasket kit and as soon as the pistons come in I'm sending the jugs out to be bored. The questions I have though are why did the piston begin to melt. I know the rod bearing probably seized because it just happens, but the melted piston and spark plug are bothering me. I don't want to rebuild the engine and have the same problem. And another thing, the spark plug wasn't tight in the head, like almost 2 turns out, would this have caused the piston to melt? I guess what I am saying is should I be worried, or does it sound like I was just riding a little 2 hard. She ran great the whole time I rode her so I'm just looking for your 2 cents.

 

P.S. This is my first post so it's nice to meet you all. I am a automotive master technician and am very mechanically inclined, but am new to 2 strokes, but I love banshees. Any help is greatly appreciated.

[endofitall9]

the spark plug shouldn't matter. the reasons for the pistons melting is because it was hot....really hot, check you water impellar and gear make sure the little pin that keeps the gear from spinnin on the shaft is ok, also check for fluids, make sure it had coolant in it, i would say check your jets but i dont think the carbs would make it run that hott, what ratio did you mix your gas?

 

WELCOME TO THE HQ

[Guest nightmare]

If your plug is loose it will suck air in and lean the bike out. That is what the washer on the plug is for . You tighten the plug and it crushes to seal it. I have seen a loose plug burn a hole in top of a piston. You don't want to crank on it to hard just snug it up tight. Once you get used to 2strokes they are kinda easy.

[baddboyy21]

The loose spark plug caused it to detonate. The spark plug needs to be seated all the way for it to dissipate that heat through the head. Your plug got extremely hot and caused the engine to detonate and the detonation melted the piston.

[endofitall9]

damn nation i better tighten plugs up a little tighter then ive rode all day to come back and see both plugs just held down by the coil wires just a couple threads holding them in, but shhhh that was on the boss' bike (Wifes)

[Machwon]

Detonation is what caused your problems. The likely culprit was the crank. It got twisted out of true and caused the havoc. I would suggest having your used crankshaft trued and welded.

[page454]

Thanks for all the info you guys.

[2twin350s]

Thanks for all the info you guys.

418802[/snapback]

what probably happened was. if under the stator looked all rusty and nasty,water and dirt got in thru the sator cover and took out theft side crank seal. then the crank main bearings,hence the chunks in the head and piston.then the crank gets loose and starts banging the plug.hence the loose plug,which leads to detonation.make sure you seal the stator cover with rtv on both sides of the gasket. that will keep your crank seal nice and clean. after your rebuild, check the jetting on your carbs. at 60 over with fmf pipes,i am taking a safe guess,you will want to be at about 280- 300 on your main jets to avoid running too lean. espeacilly if you are going to run her wide open like that. you need to be real fat on your main jetting. maybe the carbs were jetted to lean to begin with.