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1987 KDX80 Rebuild

Posted: 09:41 pm Apr 24 2015
by TheGriz
I picked up this 1987 KDX80 for $200, thinking it just needed rings and a few odds and ends. It is never that easy! My neighbor's son has been helping me in the shop and this was a great project for the two of us to tinker on.

The day I brought it home:
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1987 KDX80 Rebuild

Posted: 09:46 pm Apr 24 2015
by TheGriz
I found so many surprises:

This previous "fix" had layers of silicone and bondo on it, but was still leaking.

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This is what was under all the silicone and bondo:
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Fixed the cases properly. Tig welded a big land area to create a new tab and filed it all down nice and flat.

1987 KDX80 Rebuild

Posted: 09:48 pm Apr 24 2015
by TheGriz
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We found the clutch pressure plate was chipped. It looks like someone tried to pry the clutch out with a screwdriver. My partner is installing the new clutch:

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1987 KDX80 Rebuild

Posted: 09:58 pm Apr 24 2015
by TheGriz
The previous owner "fixed" the leaking forks by piling rtv around the fork tube and slid the boot down over it. LOL

Forks have new seals.

A pile of other parts and work completed:

Stripped and sanded down the frame
Bew ball bearings for the steer tube.
Cylinder Honed
New Wiseco piston and rings
New Stator - Had a very weak spark
Used wheels found on ebay - New brakes
New KX80 Carb
New Boyesen Reeds
New handlebars
New throttle-tube assembly from a KDX220
The plastics were sanded down and cleaned up a bit.
Used airbox found on eBAY & new UNI filter
New tires
Used side plastics found on eBAY. White vinyl added to the number plates
Fabbed a new chain guide out of aluminum
Made a chain slider work...

Probably some other stuff too... too much to remember

1987 KDX80 Rebuild

Posted: 09:59 pm Apr 24 2015
by TheGriz
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1987 KDX80 Rebuild

Posted: 10:00 pm Apr 24 2015
by TheGriz
Finally! I had started to give up hope that this bike would ever run again.

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Re: 1987 KDX80 Rebuild

Posted: 01:57 am Apr 25 2015
by KDXGarage
WOW! Good job on the rebuild! It looks nice!

Re: 1987 KDX80 Rebuild

Posted: 06:47 am Apr 25 2015
by Sullyfam
Sweet and that's one happy neighbor!


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1987 KDX80 Rebuild

Posted: 07:14 am Apr 25 2015
by TheRadBaron
Looks great. It gives me some motivation. I happen to be rebuilding an '87 KDX80 at the moment as well. I bought mine for $80, though it needed a lot of work. I'm not doing as thorough of a job as you are, either. I just want to get mine mechanically sound and reliable for family use. My wife wants to start riding trails with me and I know she's intimidated by tall bikes so the KDX80 might be a good starter trail bike for her until she gets more comfortable. She's 5'6" and about 120# so she might be a bit big for it but I think she'll like it that way.
Once she outgrows it I have a lot of young nephews and friends' kids around that could use a good trail bike to learn on. Mine has a sleeved cylinder that looks to be well done so I had it bored 0.5mm over and put in a Wiseco piston. The crank seemed good so it was left alone but I split the cases to change the crank seals and all the other oil seals. I should have it back together within a few weeks.

1987 KDX80 Rebuild

Posted: 10:47 am Apr 25 2015
by TheGriz
Thanks! I had fun working on this little KDX. After selling my 2003 220, it was nice to still have a KDX in the garage.


This had a sleeved cylinder as well. I was going to have it bored as well, but after a quick ball-hone, most of the worst grooves were gone, and I decided to go with it. I'm glad I did! She makes good compression and fired on the second kick.

It is much shorter than the 99' KX80 that I have. I'll try to take a side by side shot of the two, but at 5'6" this thing would be a bit small. It would be good to learn on at least. More mild power and easier to get a kid's (or small woman's) feet flat on the ground.

Re: 1987 KDX80 Rebuild

Posted: 09:37 pm Jul 11 2018
by Kawai man
what air filter did you buy? and carb?

I'm trying to get a kdx running and just wondering what you used. :grin: