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Yesterday me and my buddy went riding, and he was being stupid and burning out flinging mud at us trying to be funny, and after about 10 secs. the motor quit, (I think because he over reved it and blew it up) but when he went to kick it the motor won't t turn over it is seized up, so I took the top part of the motor off not the head but where the spark plug goes and the tip of the spark plug was smashed and there is sand and gravel size pieces of metal on top of the piston, but the piston looks good. My question is how to fix it and what all do you think it needs, just a new piston kit? or is it FUNKED ???

P.S. He's not the brightest crayon in the box

"Where the spark plug goes" is the head. Sand and gravel sized pieces of metal in the piston crown does not mean the piston "looks good". The least of your buddies worries at this point is the piston, that's way cheaper than what is really wrong with the motor. If the metal parts look like bronze, he's probably destroyed the lower end and that costs money.

You don't sound like you've rebuilt motors before, so rather than tell you what to look for, I would just say drain all the coolant, dry the cylinder and head, spray a little oil on the parts, and put the head back on with all the bolts loosely in the right holes and take it to a reputable shop or private mechanic if you know one. Make sure they tell your buddy the estimated cost before they do anything. Not knowing the type of bike, the repair could be more than the bike is worth.

I ment the piston looked goods as in it wasn't cracked or anything along those lines, I have rebuilt a motor before also. you are right about the head thing I ment to say the main cylinder walls I just took off the top little head. the bike is a 2001 CR 250

Not cracked... just melted. It will be allot of cleanup work.... the melted aluminum comes off with just picking it off with pick or some other tool. Chemicals will not get it off. You can get down to the nitty gritty and see what will be needed.... usually just a new piston, bearing, rings etc... a basic top end.

Your crayon buddy needs to learn how to jet his bike.

What excatly melts.

Piston and sometimes the head.

After re-reading my earlier post I may have come off harsh. That wasn't the intent, it's mostly just because I'm well,, harsh. An '01 CR250 is certainly worth a bottom end rebuild if it comes to that. But still, you need to find out what is the source of the "gravel size pieces". From my experience in blowing up a few motors, if you get brownish chunks floating around, it's usually the the bottom end that's grenaded. Which, unfortunatley, is expensive to fix, and requires special tools and experience to repair correctly.

Let us know how Crayola man makes out.

Just got done with a re-builder myself. The guy befoe me took the set screw out of the powervalve and then tried to run the engine...... not a recomended idea. Power valve came apart and one of the pins got sucked back up through the exhaust port ruining the cylinder and brand new piston. Remidy? Re-sleeved it. New piston was about $96, sleeve was $90 and labor to put in the sleeve was $80. Like new.

Just from your desription, anytime there is gravel size chunks in the cylinder area just after siezing means catastrophic engine failure hence the seizing part. You won't know what to do with it until you find out exaclty what happened and that means you will have to tear the engine down. My advice is if you have a digtal camera, use it when tearing it down so you know exactly how it should go back together. Like the powervalve assembly for instance. But until you tear it down, you won't know where you need to starton repairs.

Re: Jetting..

Maybe not. He wasn't moving. No air. Got hot. Got blowed up.

..as I understand what he was doing anyway.

Might have been stone cold, too.

Heck..Mr. Crayola maybe runs straight gas, too!!

Re: 'or is it FUNKED ???'

Most likely.

Well one of my friends that works at Harley Davidson pulled the piston out of my buddies bike today and the piston was split/cracked all over and there is pieces in the lower crank end, we pulled the crank case off the lower end doesn't look bad we are just wondering A. How you make sure you got all the little pieces out? and B. What the heck causes the piston to split and crack like that ???

beeds3000 wrote:How you make sure you got all the little pieces out??

Short of disassembling the bottom end not a whole lot. You can take the motor out of the frame, get some kero/turps, shake and flush and shake and flush and shake and flush until you are confident its all out.

Good luck...

Too bad the builder sleeved it....It's not a "RE" sleeve when it's not sleeved in the first place. That being said an iron bore isn't really a bad thing...there are pros and cons, but especially for the recreational rider a coated alum cyl is a beautiful thing. For one, an iron bore needs bored/honed in between rebuilds. Glad she's up and running though!

Re: 'What the heck causes the piston to split and crack like that ???'

220's do that off the showroom floor!

Poor piston design, casting flaws, flashing residue.

Heat, oil failure, spark plug failure (projected tip disintegration), FOD..

All sorts of things.

Re: 'we pulled the crank case off the lower end doesn't look bad '

????

A cover was removed and the crank was checked for radial play?

Or, the cases were split?

The cases were split

beeds3000 wrote:The cases were split

That's how you make sure you got all the little pieces out.