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Getting ready to send my 2003 KDX200 head and carb to Ron. I'm pretty sure this is the original top end since the bolt heads were unmolested.







Question 1
How does this look? Specifically the carbon build up and cylinder wall.

Question 2
Can I clean that carbon build up off the piston while it is still in the cylinder? If so, what is safe to use?

Question 3
Also, there was some droplets of antifreeze and dirt bits all up in this stuff as you can see in the pics. How much of this is normal?

Question 4
The spark plug tip and carb slide had a white milky type substance. What is that and what does it indicate?

Question 5
Can you tell this is my first (partial) tear down?

Looks like you had a failed head gasket....

No biggie.... wasn't too bad.

This is why you have minimal carbon on your piston.

Indawoods wrote:Looks like you had a failed head gasket....

No biggie.... wasn't too bad.

This is why you have minimal carbon on your piston.

I thought that too. AF was getting in there somehow, keeping it clean.

Do you think there'd be a problem just putting the RB head back on with a new gasket?

No reason to think so ....

re; Can I clean that carbon build up off the piston while it is still in the cylinder? If so, what is safe to use?

I have before. Yamaha Combustion Chamber Cleaner and a toothbrush worked for me, but carb cleaner would probably work too

But why not throw a fresh piston in there, while you have her apart?

Your this far don't quit! Pull the cylinder and check the piston to wall clearance and the ring end gap. If the piston clearence in within spec then install a new set of rings on your piston. Scotchbrite your cylinder, clean it up, install a new base gasket and reassemble.

From what can be seen the cylinder wall looks like some blowby on the exhaust side - traces on top of the piston in the same area. (FWIW - A piston with a little carbon on it will not hurt anything. Attempting to clean the carbon off while the piston is within the cylinder might hurt the engine - little bits of carbon or scaper materials between the piston and cylinder or forced into the ring landings - NO GOOD. Those vertical marks in that area may just be carbon that flaked off due to your head cylinder leak and not scratchs in the coating but finding out any problems and addressing them will result in a motor that should be good for 5-6 more seasons for most riders) Rings that have lost their tension or are worn and allowing blow-by will just mean you'll be going back into that engine before long anyway. Fix it while you got the time and inclination.

P.S. If it needs a new piston now is the time

I like oven cleaner to remove pretty much anything overly stubborn, and when I bought the cyclepedia manual guess what it recommended?! oven cleaner! It even took a wart off my wait no my girlfriend told me not to talk about that.

Carbon is tough stuff. Like IC said..you don't want to go scraping, carving, flicking that chit around. If you're intent on cleaning it up, put the piston at TDC, block off the piston/cylinder gap (like..yanno..tape?) and the cylinder ports. Maybe douse a rag with YCCC, let it sit on the piston crown for awhile before you attack it with an angle grinder and a #20 pad.

There isn't enough there to worry about.

That is an odd carbon pattern. It's not a little included..it's a LOT that way...with edges, even!

The gasket looks odd. Maybe it's just the flash on the camera.

What's the funny outlined hole on the head at 2 o'clock?

It does all look wet. ..which is the answer to #4...moisture.

Re: 'Those vertical marks in that area...'

I thought those were just goo from the wet kind'a smeared down. The carbon on the wall is above the top ring, ain't it? It doesn't wipe off? The gasket makes it look deeper than it really is 'cuz of the shadow?

What's the other side of the gasket look like?

An OEM build with a leaking head gasket. I wouldn't bet on it....but then...who am I to argue with a bunch of unmolested bolt heads!!??

Take that pin out of the head before you send it off. NOt a big deal...but then you'll know where it is and Ron won't have to care. I guess it's there anyway. Can't see it on the head..but there is a hole in the cylinder where it fits...USED to fit...........

OH NO!!!! You dropped it into the crankcase!!!
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jk


RE: '...told me not to talk about that.'

Her what? That's OK. I'm sure she's still beautiful. Just keep telling her she is and she'll be fine. Beauty is in the eye of the beholder and all that stuff........

Scraping the carbon off the top of the piston is no problem.
It's not that hard, so if some falls down, it's not big deal.
If have a vac, you can hold it right beside where you're scraping, and nothing will escape.

Mr. Wibbens wrote: But why not throw a fresh piston in there, while you have her apart?

Because I'm chicken. How's that for an answer?

re: "What's the funny outlined hole on the head at 2 o'clock?"
I think it was just gasket crap. It's all cleaned up ready for Ron with the aligment pins removed and safely stored away.

re: "I thought those were just goo from the wet kind'a smeared down. The carbon on the wall is above the top ring, ain't it? It doesn't wipe off? The gasket makes it look deeper than it really is 'cuz of the shadow? "
The black carbon is above the top ring, but the brown cylinder smears didn't come off with a wipe of the finger but they weren't scatches either. I didnt apply too much pressure (dabbed only) when cleaning this up a bit. Like IC mentioned, I didn't want any bits falling in there. I made sure the piston was at least at TDC during the dabbing process.

What's the other side of the gasket look like?
It's still dirty and the pics weren't that great. Maybe I post a daytime pic. It was wet, had some brown spots on it, some sticky gasket material, and grime; like sand/dirt/cap bits.

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Looks a little rough to me. I'd go ahead and pull the jug and check the piston skirts real well along with the cylinder walls. What you can see ABOVE the piston is no indication of the condition BELOW the piston. It's no real trouble to pull the jug off and check everything real well. Installing a piston is likewise a piece of cake. At the very least this way you can deglaze the cylinder walls and put some new rings in.

Some pretty good deals on "nos" kdx200 pistons around fleabay these days....

wtf is nos?

NOS = New Old Stock

juliend wrote:Looks a little rough to me. I'd go ahead and pull the jug and check the piston skirts real well along with the cylinder walls. What you can see ABOVE the piston is no indication of the condition BELOW the piston. It's no real trouble to pull the jug off and check everything real well. Installing a piston is likewise a piece of cake. At the very least this way you can deglaze the cylinder walls and put some new rings in.

Some pretty good deals on "nos" kdx200 pistons around fleabay these days....

What does deglazing entail? I've never done a top end and I'm scared "@#itless". I know I'm being a yssup but I love this bike and I'd hate to blow it up.

I have the service manual and have been studying it but nothing beats experience. I guess I'll be getting some.

Another question, the LH thread on the advancer shaft lever... is that the shaft everyone says needs to be supported? Does a wrench fit over the shaft or do you just use pliers?

It's no big deal

What could go wrong??

Mr. Wibbens wrote:It's no big deal

What could go wrong??

Great. The "pot stirrer" gives me a boost of confidence.

How important is changing the wrist pin bearing?
Is it easy to tell if it needs replacing?
Also, it looks like some Wiseco kits include one gasket. Aren't there two; one below the head and one below the cylinder? Which one are they providing?

Thanks for all the advice guys.

Some wiseco kits contain everything

Everyone says change the bearing, no one seems to have any info to back it up as I've ever heard. But you are there already and it aint much more money, so why tf not??

I found the Wiseco piston Kit (piston, rings, clips, and pin) on RM for 129 and the bearing for $13 more. Plus you can easily find (I did) a coupon for $20 off $150. So get I can get the gasket locally (almost) free. Do I need the bottom gasket as well?

I would think that if the wrist pin bearing were an issue they would include it with the piston kit. Everytime I do a top end I tell myself I don't need to change it but I still do (everytime) cause I Just can't make myself re use the old bearing. Especially since I've taken it that far apart.

I suppose for people who change their piston and rings every 3-5 races like the manual tells you then you probably don't need to replace the bearing every time. For those of us who make the top end last for years at a time it is just good sense to replace it.

No, don't hold the KIPS shaft with pliers. you'll need an open end wrench. I think it's like 6 or 7 mm. If you slide the boot down an inch or so you'll see a flat spot on the shaft. That's where you put the wrench.

You can deglaze the cylinder by using a scotch brite pad and WD 40. Just wet it with the WD 40 and run it around (not up and down) the cylinder. You'll be suprized how much better your cylinder will look.

Just hope you have little carvr sized hands instead of yeti sized hands