Piston and rings

Questions and Answers about the best carb and Head mods available for the KDX.
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ArkAngel
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Piston and rings

Post by ArkAngel »

Hi guys,

i need some help again.. I got a KDX 250 that im trying to fix up and thought i would do the top end..
So i pulled it all apart and wanted to get replacement piston and rings, i googled the number under the piston that was 4sr00 and found that it was a yz 250 piston and rings.
I want to know if you think i should put the KDX 250 piston and rings in or just got the same replacement part?
As far as can tell the dimensions of the pistons seem to be the same as the KDX.. i checked the bor and found it was about 67.50. so i don't think they done anything big to make the yz 250 fit..
I just want to know what you guys think and maybe tell me the difference in the pistons of a 2 stroke bike?
When i asked the guy that i bought the bike from he said he never done the top end on the bike... so i thought it was about time to do the top end..

Please let me know anything that you guys think or if you need any more info from my side.. all the help will be greatly appreciated

Thanks
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kwakers
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Re: Piston and rings

Post by kwakers »

you will need to identify the year of the bike and check what was stock, then measure and confirm, 67.4 mm is stock `91-`94 this link may help some

http://www.procycle.us/wiseco/wisecokaw175-500.htm
http://www.lukesracing.com/luksr/WPKD.htm


cheers

ian
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KDXohio
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Re: Piston and rings

Post by KDXohio »

I'd stick with what's in there as its been honed to match that
1990 KDX200 FMF Fatty, Answer VFC silencer, VForce 3 Cage, Wiseco Piston, KX125-J series KYB USD fork conversion, Race tech goldvalves, J series front brake assembly, air-box snorkel removed, Acerbis Headlight, KX450F Front fender, Pro Taper RM bend bars, ASV front Brake lever, MSR Clutch perch and lever, RB Head mod, 36mm PWK carb, Trail Tech Kickstand.
ArkAngel
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Re: Piston and rings

Post by ArkAngel »

Hi Guys,

i want to post some pics of the piston and barrel. the barrel and piston are smooth and i don't feel any notches or scratches in them.
I also want to find out if the dark marks on the piston could be the rings from blow-by or warn rings?

Image

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So what you guys think?
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diymirage
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Re: Piston and rings

Post by diymirage »

im not very impressed by the whole setup
there looks to be some heavy wear on the piston, aswell as the bore

a new piston will definitely seal up better and make more power then what is in there now
I would not order one from a different bike because even though the bore and stroke may be the same there are different things to consider, like the location of the wrist pin for instance
if you move the wrist pin down by about a mm you might raise the piston enough to send the spark plug through it the first time you kick it over
(on a side note, it looks like the piston from a 1990 KX 250 is identical to the 90-94 KDX250 unit)

another thing to consider is porting, who is to say the skirts of the YZ piston would properly time the ports on the KDX barrel ?
come to think of it, that might explain the hackjob done to the ports on your barrel, it looks like it was chamfered by jack the ripper


I wonder if the bike ever had any cooling issues with all that goop on the head ?
definitely something i'd want to address if I were you, and see where else this stuff is (over)used
newbbewb wrote:DIYmirage has it right.


-1996 KDX 200 woods weapon (converted to 99 green body)
-1996 KDX 200 plated street toy (barney edition)
-2003 Yamaha TTR125-L (wifeys bike)
-1997 KDX 220 project bike
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Re: Piston and rings

Post by KDXGarage »

I say cylinder needs a replate, as well as a new piston and rings, etc.
Thank you for participating on kdxrider.net. :bravo:
To post pictures from a device: viewtopic.php?f=88&t=24128
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KDXohio
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Re: Piston and rings

Post by KDXohio »

+1 on replate and piston kit then you can buy the kdx kit instead of the yz kit this time too.
1990 KDX200 FMF Fatty, Answer VFC silencer, VForce 3 Cage, Wiseco Piston, KX125-J series KYB USD fork conversion, Race tech goldvalves, J series front brake assembly, air-box snorkel removed, Acerbis Headlight, KX450F Front fender, Pro Taper RM bend bars, ASV front Brake lever, MSR Clutch perch and lever, RB Head mod, 36mm PWK carb, Trail Tech Kickstand.
ArkAngel
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Re: Piston and rings

Post by ArkAngel »

Hi guys,

thanks for all the replys.. What i have done is found a wiseco distributor in south Africa that should be able to get me a better price on the KDX 250 piston kit for me.
Kawasaki here can be a bit expensive sometimes.. But now just looking for somewhere to replate it now..
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diymirage
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Re: Piston and rings

Post by diymirage »

seriously, am I the only one who is worried by that port job ?

and it almost looks like there are some cracks in it aswell, no ?

Image
newbbewb wrote:DIYmirage has it right.


-1996 KDX 200 woods weapon (converted to 99 green body)
-1996 KDX 200 plated street toy (barney edition)
-2003 Yamaha TTR125-L (wifeys bike)
-1997 KDX 220 project bike
ArkAngel
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Re: Piston and rings

Post by ArkAngel »

I think i will take a closer look at that tonight. and let you know what i find.
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