locked up motor. PLEASE HELP!!

[KTMEXC125]

i went out riding today on my new k5 that i just got a few days ago. i started with some tight trails and i loved it! it was a tractor! a really fast tractor! after i was done barking around the trees i went out on the country gravel roads. i never got on the pipe or cracked the throttle open. i was just cruisin. i pulled it up on this little highway that runs through the area and i started out just rollin on the throttle. i probably got it up to 70-80 mph with no problem and it still wasnt full throttle. i had went for about 50-60 yards with it goin almost 80 (i was smokin by cars with ease  ) and all of the sudden the rear wheel locks up and the back end starts sliding around. i thought i was gonna kill myself. i pulled in on the clutch real quick and rolled it into the ditch. it would kick over but had little compression. and then i pushed it home 3 miles wearing moto boots. not fun. hahaha. i had a 2001 kx125 that did the same exact thing and in the same exact place a year ago and the skid mark is still there. i was haulin that time and had an antifreeze leak so it got hot. on my k5 i think the oil mixture was too lean and it was cold outside so that made it even leaner. it was the same gas that the previous owner had in it. i wish now that i would of drained it and mixed some up myself.  i know that the top end needs to be replaced and i assume that the cylinder probably has some gouges in it and will need to be replated. ive rebuilt top ends before so it wont be a problem for me. what i need is some information on cylinder replating or resleeving. a friend told me that if you resleeve a cylinder that it will never run like it used to. what would replating cost for the k5? i just started to love this bike so i want to get it up and running again. also what can i do to detune it while im going to be working on it. what headgasket thickness should i use and reed spacer and fly wheel weight should i use. and one more thing, my 500 is super loud. it has a gnarly head pipe and stock silencer. what silencer would make it easier on the ears? i live on a farm and it scares the cows and my hunting dogs

[ID KX500]

Angels were watching out for you .
Tear into it and find out if it needs a crank. Top end won't be so bad,, but top and bottom might be spendy. I suggest not de-tuning just maybe make it smooth from bottom to top (but do it the way you like while you're at it). Check with stewart here on this site when you find out what all it needs. He has many refined rebuild ideas to get the performance you want in a KX500. When you're done you may be able plow fields with it. Good luck.

[BDI]

Sounds like you already detuned it 

[k5abuser]

i help stewart and we can help . just shoot him an email and let us know what you want from your motor . watch vids on youtube under me as / k5abuser / and also the guys that set the land speed record listed on youtube under / wolbrinkrace. thier motor we built them held up though all they could throw at it in on the saltflats . wide open thorttle for about 20 plus runs . i think they are out riding it now for fun and have not rebuolt any of the motor.

[BDI]

I think a good mod for someone who wanted to take some of the bark out of the k-5 would be to recut the head. I would recut it the way that stewart cuts them but I would set the comp at 10:1. I think you would still have excellent performance but the bike would be very rider freindly. I think a full tilt stewart motor with the comp set at 10:1 would be a bitchin motocross bike.

[KXcam22]

I found that with a reed spacer, gnarly and jetting that the bike was so smooth it didn't need detuning. Cam.

[tharden]

When I got my bike it was so detuned that it looked like a grounded acrobat with smoke everywhere.  This is what I have done to my bike and my cousin who is leary of the kx500 said it was one of the smoothest dirtbikes he had road.  I have a gnarly pipe on it, KIPS valve adjusted, carb tuned, good heat range sparkplug, good air filter, using 50:1 fuel ratio, and flywheel weight.  This dirt bike is the best one I have ever owned and is one of the best trail bikes I could think of.

[BDI]

I'm not sure if it's a good idea or not but rather then killing the primary comp with a read spacer or installing a pipe that sines off way to early I would like to see how the bike runs at 10:1. I think you would have a bike that performed like a big pussycat but would still screem when you wanted it too. Just my thought

[KTMEXC125]

thanks for the help guys. i plan on tearing into it tomorrow morning. i talked to my local dealer and he thinks i'll just need a new piston and if the cylinder is in good shape i can just hone it and be good to go. i just pray that the bottom end is good and all the bearings are tight

[Hillclimb#42]

Encouraging salesman, but I predict Aluminum transferred from piston to cylinder and a hone, also will take-off plating, and take you out of round before removing it. Rings melted in the grooves. Leaned out holding it open, I guess, but you should really investigate to avoid a repeat performance.

[KXcam22]

KTMEXC125,
   It sounds like you just learned a valuable lesson, one that only comes by what just happend.  Never trust the PO.  That "recent" oil change can turn out to be last years and that new top end might have never actually happened etc.  As a habit when I get a bike I automatically change all fluids including the fuel, prep the filter and generally give it the once over, all the while resisting the temptation to take it for a spin.  I am older that you and learned this only because I have done the same as you and got the same result.  Keep positive. I'll bet that the damage is not as bad as you expect.  It's nice to have you as a member of KXriders. Cam.

[KTMEXC125]

cam,
thats exactly what i thought but only after i blew it  this is the second time i've done this! i knew the previous owner and i know that the bike had never had a new top end. its a 2003 but it was due for one. i wish i would of went through the bike before riding it but i was just really eager to ride it. come on now! its a kx500! could ya blame me?  im gonna go tear into right now. i'll try and post some pics of it so you guys can help me out

[KTMEXC125]

i pulled the jug off earlier today and man am i one happy guy now!!  the crank and rod are perfect and all the bearings are tight. there are two light scratches in the cylinder and one tiny flake. its going to need to be replated and of course a new piston is in order. where is the best place to get it replated? US chrome or max power? i dont mind paying a little more if the quality is going to be better. on another note my 1999 KTM 125 EXC is for sale so i can fund this project. if you want a quality bike shoot me an email. and here is the craigslist link, http://kansascity.craigslist.org/mcy/1074283525.html   my price may be a little high for now but im willing to bargain. i would also consider trading it for an older 500 (im hooked on the power of the k5 now!) i love my ktm and its a riot in the trails but the 500 is king of my garage now and sadly it must go

[jdcowboy]

That is a real bummer dude.  Are you sru e you found what the cause was?  As I recall your friends dad owned the bike, Assuming he is trustworthy ask him about the fuel mixture.  If he had the bike for long it is unlikely that he mixed the fuel wrong.  THus you may still have a problem that will bite you in the future again.  I will say though I have ridden a ton of 2 strokes and that was the only reason i have ever seased piston.
Good job on keeping the bike upright.....
Now what is all this talk about detuning.  I love the adrinaline rush that violent hit causes. Don't casterate your machine, just learn throttle control.

[KTMEXC125]

well when i drained the gas out of the tank it looked pretty clear. my buddies dad bought the bike in 2004 and always kept up on maintaining it.  maybe he made a mistake when he mixed some gas up, or thought some was mixed up in a can and it wasnt. im not really sure. i would guess that it was just wear inside the cylinder, the piston, and the rings. stuff is going to wear out eventually in a motor, ive learned that the hard way many times with many bikes and vehicles. what else would cause a motor to seize up like that? would light scratches in a cylinder that would cause some blow-by cause a motor to lock? it only seized for a little bit then broke free.

and there is one thing bothering me at the moment. i was inspecting my 500 and i noticed that the distance between the crank and the case isnt the same on both sides of the crank  the crank turns over fine and there is no play between the crank and the case. there is more clearance between the left side than the right. should i be worried?? im guessing that that is a problem and it needs to be centered before i put the top end back on when i get it fixed