2000 KX500 - New to me.

[Friar-Tuck]

 Rats.. sorry to hear about that Camo, it sounded like the bike was running great.  I figured if you ran the bike hard at sea level any elevation change would have been up, and worse case senario was the bike would have been too rich.
   I don't want to make any accusations, but if you don't think your brother could ride the bike any harder than you did...
Is it possible the fuel can of pre-mix got swapped out for the straight fuel?
    If I understood you, your last ride out was at the beach, so I'm figuring you were able to "See what she Had".
              The sand / dunes puts a about as hard a load on a bike as you can get.
If the bike held together under those conditions, with you piloting, I don't see how running the woods was any harder on the engine.   Now I don't Race and I'm certainly no engine guru, but I know it wouldn't take long to muller up the top end with little to no oil, the bike was jetted for sea level and it wasn't much cooler at 2500' than it was at sea level a few weeks ago. (well not enough to cause the bike to be jetted too lean at 2500')

Sorry Mate,  I was hoping the plug just worked its way loose!
   Tuck\o/         

[Camo]

It ran strong at the beach. Wheelies in every gear. Kick me off the bike when starting if I didn't follow through properly. Start and idle with it crisply pounding. No odd noises other than the normal vibration. There is no way my nephew rode it in the woods harder than I did in the sand. He ran the premix I mixed for him before I left. Maybe the fuel was bad and it detonated? Had that before in my sleds. The fuel was 3 weeks old 93 premium mixed with 108 race 50:1 with synthetic Amsoil oil. Hmmmm. I'll have to go home and investigate I guess. I wonder if the crank seal went. Plug looks decent from what my Dad said.

[Polar-Bus]

It ran strong at the beach. Wheelies in every gear. Kick me off the bike when starting if I didn't follow through properly. Start and idle with it crisply pounding. No odd noises other than the normal vibration. There is no way my nephew rode it in the woods harder than I did in the sand. He ran the premix I mixed for him before I left. Maybe the fuel was bad and it detonated? Had that before in my sleds. The fuel was 3 weeks old 93 premium mixed with 108 race 50:1 with synthetic Amsoil oil. Hmmmm. I'll have to go home and investigate I guess. I wonder if the crank seal went. Plug looks decent from what my Dad said.

post pics of the cylinder and the piston, we should be able to give you a good idea of what happened. pistons always give clues about the failure.

[Camo]

I will. I won't be home for a week. I'll have it apart next Wednesday. I heard... the motor has to come out to remove the cylinder. Any rumor to this or can I get it apart in frame?

[Polar-Bus]

I will. I won't be home for a week. I'll have it apart next Wednesday. I heard... the motor has to come out to remove the cylinder. Any rumor to this or can I get it apart in frame?

False.  Remove the head first then slide the cyl off no problems. You can pull the cyl and head together but it is a VERY tight squeeze.

[wierdo]

I had the same problem, just cut out on me, looked at every possibility, fuel, elec, piston rings etc.  had me stuffed what was wrong for ages kept having to tear down the top end to try and find the source. every thing looked fine every time,after reassembly motor would kick over then die. problem was the head studs would torque to specs but would stretch at start up, check all the studs againsta steel rule if its stretched you will see it as plain as dogs balls. ended up making new studs from some grade 8 bolts from the local caterpillar dealer and installing time-serts into the barrel. never reuse studds more than a couple of times especially  on any motor thats making any sort of compression.
Hope this helps.
Weirdo.....

[Friar-Tuck]

 Hey Weirdo Thanks for the Info.

check all the studs against a steel rule, if its stretched you will see it as plain as dogs

  You place the rule on top of the cyl where the stud exits the barrel right?   The stud pulls up, and  the material surrounding the stud "crowns" (for lack of a better term) and forces the head up.   
This has occurred more commonly in higher performance applications that I am aware of.
  The only  way to combat this is I know of  was  to countersink the stud holes.
     Tuck\o/

[duner04]

It ran strong at the beach. Wheelies in every gear. Kick me off the bike when starting if I didn't follow through properly. Start and idle with it crisply pounding. No odd noises other than the normal vibration. There is no way my nephew rode it in the woods harder than I did in the sand. He ran the premix I mixed for him before I left. Maybe the fuel was bad and it detonated? Had that before in my sleds. The fuel was 3 weeks old 93 premium mixed with 108 race 50:1 with synthetic Amsoil oil. Hmmmm. I'll have to go home and investigate I guess. I wonder if the crank seal went. Plug looks decent from what my Dad said.

did the 93 premium have alcohol?  alcohol doesn't mix well with 2t oil. One our local vintage racers lost a Husky 500 topend when he mixed the alcohol premium with his race fuel, he had never mixed the 2 before. ethinol fuel deteriorates much faster, too.

[Motorrad]

It ran strong at the beach. Wheelies in every gear. Kick me off the bike when starting if I didn't follow through properly. Start and idle with it crisply pounding. No odd noises other than the normal vibration. There is no way my nephew rode it in the woods harder than I did in the sand. He ran the premix I mixed for him before I left. Maybe the fuel was bad and it detonated? Had that before in my sleds. The fuel was 3 weeks old 93 premium mixed with 108 race 50:1 with synthetic Amsoil oil. Hmmmm. I'll have to go home and investigate I guess. I wonder if the crank seal went. Plug looks decent from what my Dad said.

did the 93 premium have alcohol?  alcohol doesn't mix well with 2t oil. One our local vintage racers lost a Husky 500 topend when he mixed the alcohol premium with his race fuel, he had never mixed the 2 before. ethinol fuel deteriorates much faster, too.

What oil was he running and what race FuEl??   I bet the oil and race fuel were more to blame...   Some oils don't like low S.G.

[wierdo]

Hey Friar hows it goin? I had to remove all the studs and layed them against the steel rule to find the offender(s). But i also had  the crowning issue as well, if you use time-serts to repair the threads, when installing the tools supplied will countersink the hole for you and the insert will sit flush with the barrel deck. I wont use helicoils anymore they are only marginaly stronger than the original threads cut into the alloy barrel, I have found the time serts to be a much stronger option. they also have the ability to be removed with a ezy out, pull it out and reinstall a new one,  2 minutes good as gold..try that with a helicoil..
Weirdo.... 

[Friar-Tuck]

Hey Weird,
 Just wanted to be certain I understood your point, thanks for the reply.
    I'll have a go with the time certs next time the need arises.
  Tuck\o/

[Polar-Bus]

I've pulled helicoils out many times. I don't advise it but if a helicoil gets "cross threaded"  trying to install the insert you have no choice. Pry up the first top thread wire, then grab the wire with vice grips, and yank the wire right out.

[Camo]

Well... The verdict is in.

Whoever did the top end either used the old wrist pin circlip or didn't install the new one correctly. Yep, chewed the crap out of piston, cylinder and head. Some people should never pick up a wrench. I'm choked. It has an 86mm piston and I'm not sure 87mm will do the job. The gouges are ugly. I'd attach a pic but can't with my phone on here.

[Camo]

[Goat]

That sucks bad. By the looks of it they just didn't install the clip properly. I always make sure the clip opening is at the top once installed in the groove.

That cylinder's gonna take some major work. The gouges on the lower port look pretty d**n deep. May have to do a big bore kit.