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Old 07-16-2014, 01:58 PM   #1
disgustipated OP
Joined: Mar 2011
Location: Denver, CO
Oddometer: 111
A Dollar Paid Per CC

I was looking on craigs for no good reason and noticed a cheapo KDX posted. The seller claimed it ran but needed some work and was asking a few hundred bucks, IIRC. I called them up and went over that evening while it was single digits outside in early December.

The bike started right up with a snappy ring ding but I could see smoke coming out of a gap between the exhaust and cylinder. The more I looked at this machine the more I noticed things were awry. It needed rear brake parts out the whazoo, no air box, but had a dry street filter, soon to be trashed chain, exhaust leaks, the wrong front brake cable(to be discovered), and who knows what else.

So, intelligently I pursued a deal for this glorious bike and struck a bargain at $175, he called it the cold weather special. We put it in the truck and I was excited at the prospect of an older than thou, two stroke, six speed, air cooled, '81 KDX 175. Sweet brah!

The next morning I took it out into the alley for a first ride seeing as it was sunny and in the teens with fresh snow glistening on top of the dumpsters and strewn garbage along the fences. I fired her up and made as much noise as my five points neighbors in Denver. But something seemed amiss as I figured I should be losing traction left and right as I manipulated the throttle, luckily the bike had no power though as this is when I realized the front brake didn't work anyways. Safe combination I guess.

Okay, no brakes and no torque, so back to the garage we went and that's where the bike sat, waiting for my return with a compression tester.

Did I get what I paid for?

disgustipated screwed with this post 07-18-2014 at 03:16 PM
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Old 07-16-2014, 09:29 PM   #2
disgustipated OP
Joined: Mar 2011
Location: Denver, CO
Oddometer: 111
Ebay Time

I started searching Ebay for the stuff I was adding to the expanding list of necessary upgrades. First was a manual and rear brake stuff, along with a right foot peg. While I waited for that stuff to arrive I monkeyed with the front brake, drum of course, and I just couldn't get it adjusted right. Eventually I decided it wasn't the right cable and got a new one, which works great. Got the rear brake working too once the parts came in. I had also ordered the exhaust gasket and ring for between the cylinder and expansion chamber, hoping this would cure its seemingly low compression. Nope.

So a trip to "harbor you know what" was in order. Testing the compression on the kdx resulted in 30 psi. Thinking I did it wrong, and I probably did, I did it again, maybe still wrong. Same results. Manual says it should read 120. Huh.

Should have done a leak down test. I figured if it was that low it was leaking at the crank seals too, not just the top end. Time for a full rebuild.

Started ripping it all apart, head came off. That was quick and easy. Next the jug, that was easy too, these two smokes are fun!

Pulled the piston off and there was some scoring which matched the cylinder. The connecting rod seemed to have a lot of play, no bueno. The top end was looking fugly so I figured the bottom end couldn't be that spectacular itself.

I shipped off the cylinder to get replated with the new piston.

Meanwhile I started getting ready to split the case. Let me just say that the acetone/ATF penetrating fluid is the bees knees, nothing helps more than that stinky red fluid! After struggling with a stuck flywheel it all came off pretty well.

With the side to side play in the con rod I figured the big end bearing ought to be replaced. I talked to a guy about rebuilding the crank with new washers and a bearing, but he says with the play in the rod it will need a new rod or it will just wear out the new bearing. Is this true?

It would be nice to not replace the rod as that will be a whole rod kit and I already have all the pieces minus the rod.

The other thing the guy said was that the crankshaft itself was probably shot because of grooves worn in the shaft by the seals. Any two cents on that one?

I may have found a crank a couple hours away, but the guy doesn't know if it's from the same year kdx or from an 80 kx 125, though I am under the impression they may even be compatible, according to my google-fu.

So that's been the last several months of wrenching, hopefully I can figure out these crank issues and get this smoker going. Unfortunately the VFR has been eating up some time and money. There's only a few more parts I really need from ebay to get this thing going. Though I should probably sort through the suspension while it's down…. there's always something.
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Old 07-18-2014, 01:30 PM   #3
disgustipated OP
Joined: Mar 2011
Location: Denver, CO
Oddometer: 111
Speedi Sleeves

A question for y'all, should I even consider using speedi sleeves for that crank seal groove on the shaft?
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Old 08-02-2014, 05:59 AM   #4
No Marks....
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Joined: Sep 2009
Location: Michissippi & Nuevo Mexico
Oddometer: 2,318
Early to mid 80s KDXs were notorious for having terrible brakes and forks. Maybe a later model (USD fork?), wheel and brakes will work(90s KX125?) . That bike really needs it. The rear brakes wore out liners really fast and did not work well. The engines are really nice torquey units though. You do know that a rod is supposed to have some play laterally do you not? It should have NO up/down play on either end though.A crank can be tested at both ends for up/down movement with someone holding the bike down and should have NO side movement.

I know I would assume a 33 yr old engine needs a complete rebuild in every way including a clutch/ gearbox inspection as well. I never run these old bikes when I get them as this can cause additional damage to their internals if something is left loose.

They are great little engines in a terrible chassis. Maybe the engine in a 90s KX frame instead?? Then it would run ,handle and be trouble free.
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Old 08-26-2014, 06:10 PM   #5
Gnarly Adventurer
Joined: May 2013
Location: Wichita Kansas-USA
Oddometer: 109
Originally Posted by disgustipated View Post
A question for y'all, should I even consider using speedi sleeves for that crank seal groove on the shaft?
Speedi sleeves are used in industry everyday with perfect success.I wouldn't hesitate saving a crank with'em
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Old 04-08-2015, 09:50 PM   #6
disgustipated OP
Joined: Mar 2011
Location: Denver, CO
Oddometer: 111

Upgrading the fork and shock definitely are on the list of upgrades, including brakes, but just imagine how much faster of a rider I will become with crummy drum brakes and no compression braking. More seriously, I look forward to the differences in riding a two smoke.

This thing ain't running yet, hopefully that will happen soon and then I can drool over potential mods. The clock is ticking… literally as my bsc roommate will be aiming her sights at me next.

On the plus side, I ended up scoring a used crankshaft off of ebay. Unfortunately, it showed up and didn't match the one which was removed from the engine, wtf. After further inspection the recently purchased crank resembles the one in the service manual, unlike the crank that was removed.

Recently I got a new complete gasket set and an air filter. Parts yet needed are an air filter cage, air box cover, and I just broke the clutch lever bumping it in the garage, so I needs me one of them.

The cases need to be cleaned out, including some grit in the bearings for the tranny and whatever else, the crank bearings are being replaced. After that I can begin the assembly process, and start buttoning that thing up.

Lately Ive been wrenching on the truck, which has truly needed it. New motor mounts recently, as the others were busted in pieces. Im hoping to get a locker put in the rear diff before summer hits, and maybe fab some rock sliders. Life has been crazy busy lately, I just finished 8 weeks on a paleo plan and I am feeling great! That means lots of time spent in the kitchen. Salsa and bachata lessons are keeping me feeling fresh and the VFR800 is getting my throttle therapy sessions in, life is good.

Here's to getting that green machine smokin.
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Old 04-08-2015, 10:26 PM   #7
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Joined: Jun 2008
Location: Cantwell, AK
Oddometer: 453
$10/cc. Best of luck. 1000 piece puzzle at $1.80 per piece.

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