93 KX 500 Rebuild

[Jeff90lx]

Hey Guys!

  So, I'm new to the two stroke world. But I bought a 93 Kx500 a couple months ago and it has been a blast to ride until about 2 weeks ago when it died on me and I couldn't get it started. Anyway after doing some troubleshooting it had about 50 PSI of compression. Not good. So I tore the top end apart and the piston looks terrible. I will take some pictures tonight when I get home but I was wanting to get some opinions on who I should send the cylinder to? I want to get it re-plated and get the intake and exhaust ports reworked (Sharpened) and get the KIPS valve cleaned and reworked also. I'm looking to go with a Wiseco Piston kit. Any advice is appreciated... Thanks Jeff 

[Foxx4Beaver]

welcome to the site Jeff.

1st, scratch the idea of Wiseco!....go with a Wossner.
Either PowerSealUSA, or Millenium Tech are the best places to have your jug plated.
Our member Sandblaster may be able to rework the ports.

[Jeff90lx]

[Jeff90lx]

Has some deep gouging near the exhaust ports, any ideas on what went wrong? Any piston experts out there?

[b4himdude]

Take foxx's word on the Wiseco. For some reason the wrist pin bearing loves to disintegrate. Happened to me and another few members. Go with wossner. I've had good luck with plain old pro X but I inspect the cylinder frequently as well

[Jeff90lx]

Thanks for the input guys,

 I found a piston guide but I can't get the thing to load for some reason... I just don't want to put this thing back together if the issue that caused it is not resolved. I will be sending the cylinder to Millennium Tech. to get re-plated and will probably go with the Wossner piston as suggested. The few people I have talked to about it say that it looks like some kind of lean condition that caused it, however from what I've read... If the bike had an air leak it would have been running funny prior to giving up the ghost. It's just weird because the bike ran great right up to the end... So I'm a little stumped 

[sandblaster]

Do yourself a huge favor and check the crank for wear between the rod and the crank halves.
Get a feeler gauge and stick it in there as shown below:



.016" -.020" is factory new specs.
You can run the crankshaft all the way to .028" before it's reached it's service limit.
If it's out of service specs it's time for a full rebuild.

If it is good you could install the new top end.
However, if you choose to only replace the top end, either do a leak down test yourself or have a shop do it to determine your seal condition. If it won't pass a leak down test then you know it's time to replace every seal or you risk burning up your new top end.

If I were you I would disassemble the rest of the engine and at a minimum replace every, bearing, washer, snap ring, bushing, seal, and gasket possible. I would also carefully inspect the shift forks, drum, and gear dogs.
Why? Without knowing the true history of that engine and no leak down test done before it was disassembled, you have no idea what you have. You could drop some serious coin into the top end and then fry it shortly thereafter.

We have heard too many stories of guys getting frustrated and selling their K5's for scrap because they did not understand the risks of not checking a few things...

[Jeff90lx]

Sandblaster,

It looks like you are in Oregon. I'm up in Washington, are there any local K5 guru's I could take it to for a full rebuild?

[sandblaster]

I don't know any in Washington off the top of my head.
I'm about 2 hours south of the Washington/Oregon border in Eugene.
Some others on this site may know of someone closer..

[jethrobolas]

Ha! Bought a running but clapped 93 couple years ago. Rode it twice and tore it dkwn. One ride was the purchase test. Accumulated goodies for a year.
Finished it up this spring. New tire, new wossner purchased from powerseal with replate, mains with seals, squish and compression release by Larry Wiechman, gasket and seal kit, chain and sprockets, couple trans bearings, clean and grease all chassis bearings, fresh brake juice, throttle cable, and blahblah.
Fired it up. Rolled my track cautiously. Around the track again with a bit more gusto. Open it up to run the front yard trail. Found air near my driveway on the k5 that no other bike could ever find...then skidded into a stack of a dozen utility poles laying in my yard. Hard.
Out of work for 6 weeks. Fractured tibial plateau (lucky that was all.....3 cartwheels before MY first bounce according to several of my sons buddies). New handlebars. New grips. Little tweakin' on the subframe. Sat until this October when I posted it on cl (plenty other toys).

Finally, after 4 or 5 years of talking about it, took my son to badlands ohv area and I chose the k5. Stock but fresh everything. He took my kdx200 of the same vintage. We had a blast! The k5 is no longer listed!



https://youtu.be/d0nVPqWhb28

Went from a 60 pilot to a 55. Blubbering like crazy. Video is with a 52, stock needle, clip all the way at the top. Still feels rich at small throttle and idle. Feel like i checked float level already, but winter is here and I do have a nice place to wrench on it during winter.....

Threadjack over.


Powerseal did find cracks in my transfers (I think, or maybe exhaust) but money cures almost anything.

With the proper tools, a manual, a bit of mechanical aptitude and this forum you could probably get it up to snuff with a minimum of outsourced work. Just sayin....

[Jeff90lx]

Well, I finally got around to taking measurements... I can fit .030 on both sides of the rod pretty easily... must be time to do the whole thing. Anyone have recommendations on full motor rebuilds? The closer the better... I'm in Washington. I could probably handle it, I would just prefer it gone through by an expert.

[Jeff90lx]

Well, I finally got around to taking measurements... I can fit .030 on both sides of the rod pretty easily... must be time to do the whole thing. Anyone have recommendations on full motor rebuilds? The closer the better... I'm in Washington. I could probably handle it, I would just prefer it gone through by an expert.

Also forgot to mention I found some cracks along the intake bridges... So maybe that's why she decided to let go... Now more than ever, I think I want to send this to somebody to go through it and fix any other outstanding issues. Sandblaster, are you looking for more work? Does anybody else have any recommendations for good thorough KX500 engine builders?

[umberto]

I would definitely send a PM to Sandblaster.  Your motor will come back looking and running better than new.

[1FAST450R]

i used PowersealUSA and couldn't be happier. Definitely use the Wossner.

[AfricaOffroad]

Not sure if it's the picture, but piston looks like it has major damage on its crown from detonation.