Kdx 200 Piston dome cracked.

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fuzzy
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Kdx 200 Piston dome cracked.

Post by fuzzy »

Yes, it also appears you have a piston for a piston port (not reed) engine.
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Re: Kdx 200 Piston dome cracked.

Post by nab »

The outside of the box I ordered said kdx 200 piston, I placed the order through Rocky Mountain atv.
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Julien D
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Kdx 200 Piston dome cracked.

Post by Julien D »

The height could matter. The older pistons had a small hole like that, the larger ones a window like you see on your new one. Can you get a pic from the side showing the wrist pin hole? The height from the wrist pin up would matter much more than from the wrist pin down...
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Kdx 200 Piston dome cracked.

Post by Mr. Wibbens »

nab wrote:
Could the new piston being taller have anything to do with it?

ya think? :kick:
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Kdx 200 Piston dome cracked.

Post by gregp »

One of those pistons is incorrect for your bike! I suspect the broken one is the *wrong* one! :shock:
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Kdx 200 Piston dome cracked.

Post by nab »

I emailed the company I purchased the piston from to see what can be done......

I will get some more pics tomorrow, It looks like the wrist pin hole is in the same spot despite the skirt height being different, however the gap between the rings appears to be greater on the new piston I purchased.
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rbates9
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Kdx 200 Piston dome cracked.

Post by rbates9 »

I just did a top end on my 200 and the Pro X box the piston came in was for a 86-06 KDX 200. The skirt dimension is some what irrelevant. The wrist pin to the top is what matters.
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Kdx 200 Piston dome cracked.

Post by canyncarvr »

Any marks on the head? That isn't likely to say much about what happened 'cuz it's going to be a chicken-or-the-egg kind of thing. Contact to the head squeezed the land, pooched the ring, it snagged, then broke stuff? Or..after the piston was damaged, THEN it hit the head?

Somewhat of an aside at this point, but did you find that one ring fit better in one piston land over the other? ....and then installed them where they best fit?

The rings are supposed to be the same thickness as far as I know, but I've always found one ring to be too tight in the top land.

Yeah...what's the pin-to-top distance..the height of the new piston compared to the old?

Make some similar measurement on the cylinders. What if the 'new' cylinder had been cut due to someone's bright idea of raising the engine compression (raising the piston in the bore).

There is no radial movement in the rod (big end bearing)?

Another btw...but the damage in on the intake side, NOT the exhaust side. There was no 'snag' on the exhaust port.

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Re: Kdx 200 Piston dome cracked.

Post by nab »

yeah, I noticed the skirt was taller than stock before I installed it and was not concerned. Looking at the wrist pin to the top of the of OEM vs. the Pro X I received looks slightly taller. I figure that the distance is probably negligible, but maybe not. I am not afraid to admit I could have F'd something up, but I just can't figure out where or what I could have done to cause a failure like this. I am more afraid to through more dough at another top end and find out that my cylinder was messed from the get go or I got another bum piston. The gap between the two rings is also slightly larger than OEM, again probably nothing to sweat and just an improved design. I'm just concerned because the only time I have blown a top end so quickly was building a 50cc motor and there ended up being metal in the crankcase. Found that one out really quick. :cool: Hopefully I can get down to the bottom of it and be ripping again.

On a side note anyone on here into mopeds, just finished this build.... 70cc single speed tops out at 48mph. stupidly fun :rolleyes:
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Kdx 200 Piston dome cracked.

Post by nab »

canyncarvr wrote:Any marks on the head? That isn't likely to say much about what happened 'cuz it's going to be a chicken-or-the-egg kind of thing. Contact to the head squeezed the land, pooched the ring, it snagged, then broke stuff? Or..after the piston was damaged, THEN it hit the head?

Somewhat of an aside at this point, but did you find that one ring fit better in one piston land over the other? ....and then installed them where they best fit?

The rings are supposed to be the same thickness as far as I know, but I've always found one ring to be too tight in the top land.

Yeah...what's the pin-to-top distance..the height of the new piston compared to the old?

Make some similar measurement on the cylinders. What if the 'new' cylinder had been cut due to someone's bright idea of raising the engine compression (raising the piston in the bore).

There is no radial movement in the rod (big end bearing)?

Another btw...but the damage in on the intake side, NOT the exhaust side. There was no 'snag' on the exhaust port.
I did find that one ring fit better than the other, The bottom ring definitely would not fit in the top rings place.
The cylinder I bought was supposedly NOS, but that could be a lie...
The top ring of the PRO X piston starts at the bottom of the OEM piston so the ring definitely sits slightly lower, I don't have a decent camera with me so crappy phone pics to follow. :blink:
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Re: Kdx 200 Piston dome cracked.

Post by nab »

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Re: Kdx 200 Piston dome cracked.

Post by canyncarvr »

Re: The last pic..

Height looks to be the same? Would you agree?

Not a lot to worry about regarding piston land placement. Gott'a figure Pro-X has some idea what they're doing.

How's the head look?

If you're thinking of a fix/bore/replate, PowerSeal does an excellent job. Mr. Black recommended them.

IF you go that route, maybe ask them if they could do a post mortem on the setup?

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Kdx 200 Piston dome cracked.

Post by scheckaet »

+1 on powerseal, they did my last replate 2 years ago, still satisfied. I'd use them again.
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Kdx 200 Piston dome cracked.

Post by fuzzy »

Dude, the only thing the same about those pistons is that they are both 66mm (based on your comments). I'd be on the phone with RMMC/Pro-X ASAP. Well, I would not have have run the piston, but hopefully they will make it right.
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Re: Kdx 200 Piston dome cracked.

Post by CoronasAndChips »

nab wrote:

On a side note anyone on here into mopeds, just finished this build.... 70cc single speed tops out at 48mph. stupidly fun :rolleyes:
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