Maintenance & Technical > KX500 Original

Fixing problems with new (old) bike. - Running

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MeanGreenMachine:
I recently got a 1990 KX500, and after riding the bike just enough to fall in love with it, I'm finding out that the previous owner was not all that honest about it's condition.

Things I've found so far:

- Water in transmission, milky oil: I found that the water pump seal was bad, and in fact, had silicone over a crack in it... Minimal shaft play, unable to feel any groove in the shaft with a screwdriver or a fingernail, so I just replaced the seal. Milkiness returned once, but it'll probably take another change or two before I know if it's gone for sure.

- Frame crack at the top near motor mount: Ground/notched, MIG welded and painted over. Seems to be holding fine.

- Stripped out drain plug: It came with a cut off 1/2-13 bolt in it, which then stripped. I made a guide jig and put a Perma-Coil in it to bring it back to 1/2-20. Then I installed a Fumoto F101 drain valve with about 1mm of metal "wall" left. It seems like it'll hold, though I don't exactly want to torque it too hard. The valve is well constructed and protected by my skid plate, so it should be safe. Should make changing oil easy, anyways.

So ok, it looks like I got it under control. I come home today and check the bike over in preparation for some badly needed riding time tomorrow and discover:

- Oil leaking from output shaft/chain sprocket: Must be a seal, unsure if installed from the outside or inside.

- Whirring noise at idle: Sounds suspiciously like the kind of noise a roller bearing makes when it's worn out. I pull the stator cover off and push/pull on the crank and notice that it wiggles up and down and side to side very, very slightly, though you can feel it and hear it tick when it moves. Also, the crank has some end play as well, when pushed or pulled directly. I turn the flywheel with my hand and notice that there's a very slight slack before the piston/rod move as well... Looks like I need a full rebuild. d**n it!

So, it looks like I won't be making it to Pismo after all. Further more it looks like I'll be sitting out on riding season trying to get this thing put back together. Does anybody have any ballpark estimates on how much I'm looking at to go through the entire engine, bottom end and top end rebuild, with crank, rod and new piston? Even though I got the bike for cheap and have become completely addicted to it, I could use some encouragement... I'd appreciate any information!

sandblaster:
The good thing and the bad thing about a K5 is that they can run a long time completely worn out if your not too hard on them but yours sounds like it is really in need.
At a minimum.... a crank rebuild, top end plating and piston, bearings, and seals, your looking a 1K minimum and of course, that's doing the work yourself and the sky's the limit on cost.
If you find out that 3rd gear is bad which is common, there's a couple of hundred more, if the exhaust valves are worn out, there's a few hundred more, ect, ect..
You really won't know until you get into it.
If I were you I would read this build..
http://www.kxriders.com/forums/index.php/topic,8717.0.html
And
http://www.hallbergs.net/kx500/
And
http://www.kxriders.com/forums/index.php/topic,8890.0.html
Of course, this is the right site for K5 info and rider sympathy  :lol:
Oh.... save a few bucks and buy a Clymer Service manual...

MeanGreenMachine:
Yeah, I figure that my biggest problem right now is the crank mains and the rod bearings. It's funny since I compression tested it and ice cold, I was getting ~145 PSI, and looking through the exhaust port, the bore looked undamaged and KIPS valves moved freely. Obviously if I go through the bottom end, I'll send the top end for plating and get a new piston as well.

The pisser is that we were supposed to go to Pismo in two weeks... There's no way I can get parts out and back in time to have it ready. The guys are hounding me to "just ride it till it breaks", which IMO is probably a great way to end up with 10 times the damage and parts costs.

So what places do you guys recommend for plating? Millennium? US Chrome? Powerseal? What about crank rebuilding? I read about a place called Crank Works, but could use some recommendations. Probably time to start planning...

sandblaster:
K5's are notorious for wallering out the left main bearing journal on the case.
The more you ride it loose, the greater the chance of damage.
Also, if you ride it enough with a loose piston, the greater chance of breaking off a piston skirt and munching a set of cases...
But hey, new cases are available for about 450 bucks  :-o
For a crank rebuild I would sent it out to Pinsonnault Racing for a rebuild, weld, true, and balance.
http://pinsonnaultracing.com/
Your engine and hands will thank you from the reduction in vibration.

Plating?
I'll let other chime in...

81cr450:
US Chrome +1

Jug came back beautiful within .0002 , the finish was sweet, sealed up quick

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