first 2 stroke rebuild

[black]

So i'm diving itnto this KDX 200 ( 1994)

Just finished rebuilding the rear shock ( it was pretty easy actually)and tore apart the top end ( my first time)

Also wound up cleaning the KIPS valve (lots of gunk) as supposedly the gears are fairly easy to break and reduce the top end. They were in fine shape but I swapped out some newer steel gears from from the UK.

Looking at the piston and I'm not sure how to read it.
Take a peek and see if you see anything. the bottom end seems to be "chipped"( new piston doesnt have this) And there is the "smearing" on the side. i f ifrag a fingernail across it I do feel a little itty bitty ridge Top was caked in carbon



As far as measurement the width is in spec and the same size as the replacement.

Anything i need to triple check when replacing it?

Top

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The screws holding the top cylinder are also going to get cleaned as well as they're pretty rusty etc.

[Kurlon]

I'd like to know what damaged the skirt of that piston, that's clearly not right. Is that on the intake or exhaust side?

[Pigman]

Piston toss it and see how bad and deep the scoring is in the Cycl.... thats your biggest prob

[black]

I believe it the intake side as it's on the opposite side that the arrow points to on top of the piston.

How would I check the scoring is inside of the cylinder? I eyeballed and ran my finger. And seems pretty smooth.

[gregp]

Damage appears to be on the intake side. Those small holes on the other (exhaust) side keep lube on the transfer port bridges. I agree that it looks like the motor ingested something hard at one point.

[gregp]

Feel the cylinder with your fingernail to see if your nail "catches" anywhere. KDX cylinders are pretty durable, and coated cylinders can be deceiving - sometimes the aluminum from the piston gets smeared on the hard surface, and it looks like scoring. Smeared aluminum can be removed pretty easily.

[black]

so with the chewed piston.... necessary to break down the bottom end?

[Paul_E_D]

The likely culprit is the powevalve flapper.

[black]

hmmm.. so necessary to tear down?
I took apart the KIPS valve etc and cleaned up and replaced the old( no signs of wear I believe) with new steel ones. are those the Powervalve flappers you speak od?

[Paul_E_D]

The actual part that opens that closes, not the spindles. It it is out of adjustment it can contact the piston.

[black]

mines a 94... i believe the 95 and up only have that.

[typeone]

it's hard to tell from the pics but when i first looked, i wondered if someone had modified the piston for some reason, like clearance. the break looks very clean, almost chamfered a bit and very symetrical.

how does the case look below the intake side? any sign of tampering? how about the intake side of the cylinder? any weld + grind?

reason i'm wondering about this is because i've seen some seriously fucked up vintage Husky pistons that PO's modified themselves... some looked like they used primative stone tools... NEVER underestimate the mechanical wonder of a dirt biker

to answer your question about breaking down and inspecting the bottom end, if that large piece really did break away... Yes.

[typeone]

check out the second piston from right ... hmmm

[black]

check out the second piston from right ... hmmm

yup that looks like mine.
Dont think there is a way around it. break out the bottom end.

Now to replace bearings or not?

I need to to look at the cylinder closer and the case.

Not sure. I'm just searching for a piece of metal and dont mean to ride this bike a ton ( specialty woods bike and buddy bike if you will)

[typeone]

but what i'm saying is it might not be broken at all. could be modified by a PO to look/work like a newer gen piston OR it's just a cheap cast piston with very rough edges.

EDIT: btw, i'm totally taking guesses here, hard without the parts in front of you but when i had that thought, then found that pic above... it makes you wonder.

[breakdirt916]

dirt bikes suck

when the bottom end is off, might as well do the crank bearings and seals...(what is it...$90?)

actually while the crank halves are apart, just rebuild the the crankshaft at a machine shop (what is it....$90?)

actually while the crank halves are apart, inspect all the transmission spacers/shift forks and replace it while you're there (what is it....$90?)

actually while the crank halves are apart, inspect all the transmission bearings in the cases and replace them while you're there (what is it....$140?)

actually while the crank halves are apart, inspect the seals for the shift lever, check for groves on the water pump impeller, and replace them while you're there (what is it....$180?)

....and it goes on...dirt bikes suck

wash out the combustion chamber with water and make sure no metal flakes are seen, button up the top end and sell the damn thing before it 'splodes!!!

[black]

but what i'm saying is it might not be broken at all. could be modified by a PO to look/work like a newer gen piston OR it's just a cheap cast piston with very rough edges.

EDIT: btw, i'm totally taking guesses here, hard without the parts in front of you but when i had that thought, then found that pic above... it makes you wonder.

I'll take a look at the original piston... see if its a cheapo etc... breaking the bottom end doesnt seem "hard" I just need time. I need to get my xr650r on the road

seeing what the KDX board says. but I need to look at the cylinder again. But you're right the chips seems like a caveman trying to sharpen a knife type nicks

[Paul_E_D]

Hmmm, looks like it might be a cheap piston. I would put a new top end in and carry on. It's not much work to tear it back down it something is bad in the bottom end.

p.s. I forgot that the rollers ARE the valves in those older KIPS.

[black]

dirt bikes suck

when the bottom end is off, might as well do the crank bearings and seals...(what is it...$90?)

actually while the crank halves are apart, just rebuild the the crankshaft at a machine shop (what is it....$90?)

actually while the crank halves are apart, inspect all the transmission spacers/shift forks and replace it while you're there (what is it....$90?)

actually while the crank halves are apart, inspect all the transmission bearings in the cases and replace them while you're there (what is it....$140?)

actually while the crank halves are apart, inspect the seals for the shift lever, check for groves on the water pump impeller, and replace them while you're there (what is it....$180?)

....and it goes on...dirt bikes suck

wash out the combustion chamber with water and make sure no metal flakes are seen, button up the top end and sell the damn thing before it 'splodes!!!

I hate you for pointing that out and for mostly..... being right

[carsick]

I think the most compelling question is, why take a KDX apart at all? Just run 'er!

[typeone]

Hmmm, looks like it might be a cheap piston. I would put a new top end in and carry on. It's not much work to tear it back down it something is bad in the bottom end.

p.s. I forgot that the rollers ARE the valves in those older KIPS.

i agree, especially since this is a spare, older machine. fill up the case with cheap 2T oil, cycle the crank, dump it into a strained container and see what comes out. repeat X times. no scary bits? just freshen the top end.

this assumes the cylinder isn't torn up to shit and crank isn't flopping around in there

[number9]

dirt bikes suck

when the bottom end is off, might as well do the crank bearings and seals...(what is it...$90?)

actually while the crank halves are apart, just rebuild the the crankshaft at a machine shop (what is it....$90?)

actually while the crank halves are apart, inspect all the transmission spacers/shift forks and replace it while you're there (what is it....$90?)

actually while the crank halves are apart, inspect all the transmission bearings in the cases and replace them while you're there (what is it....$140?)

actually while the crank halves are apart, inspect the seals for the shift lever, check for groves on the water pump impeller, and replace them while you're there (what is it....$180?)

....and it goes on...dirt bikes suck

wash out the combustion chamber with water and make sure no metal flakes are seen, button up the top end and sell the damn thing before it 'splodes!!!

That's basically how my El Camino project went.

Degrease the engine (in the car) to get rid of decades worth of grease and oil? Might as well just yank the engine out and do it properly. (free)

Hmm, if it's already out of the car, might as well pull the heads and inspect the pistons. (free)

Hmm, if the heads are off, might as well put new pistons and rings in. (+$100)

Hmm, if you're gonna put new pistons in, might as well put high-compression ones in. (+$200)

Hmm, if you're gonna put high-compression pistons in, might as well put new rods in as well. (+$200)

Hmm, if you're gonna do new rods, might as well do a 383 stroker kit. (+$700)

And that, my friends, is why it's in my garage and hasn't been driven in 4 years.

[black]

That's basically how my El Camino project went.

Degrease the engine (in the car) to get rid of decades worth of grease and oil? Might as well just yank the engine out and do it properly. (free)

Hmm, if it's already out of the car, might as well pull the heads and inspect the pistons. (free)

Hmm, if the heads are off, might as well put new pistons and rings in. (+$100)

Hmm, if you're gonna put new pistons in, might as well put high-compression ones in. (+$200)

Hmm, if you're gonna put high-compression pistons in, might as well put new rods in as well. (+$200)

Hmm, if you're gonna do new rods, might as well do a 383 stroker kit. (+$700)

And that, my friends, is why it's in my garage and hasn't been driven in 4 years.

i'll trade you a kdx I have for your el camino

[black]

I think the most compelling question is, why take a KDX apart at all? Just run 'er!

yeah... i know I know. Major reason was ...
the swing arm was seized. so replaced that then slowly thought I could rehab it and "learn", which I am
I will probably just rinse the case and see what falls out.

My next step afte rthat is rebuild the forks..... just because

I'm even thinking of powdercoating the frame.... because

[number9]

i'll trade you a kdx I have for your el camino

The KDX is probably worth more.