KX Riders

Maintenance & Technical => KX250 / KX125 => Topic started by: tracks on June 05, 2014, 12:59:17 AM

Title: Kx250 1986 correct piston size for my engine, what to order??
Post by: tracks on June 05, 2014, 12:59:17 AM

Hi all,

I believe I need to get a new piston kit or maybe just rings??

I have some pictures below to try and show the condition of my cylinder and piston - how do you know when you just need to replace the rings or the piston as well? I did a compression test and it was low at something around 25/30PSI (I'm not sure how accurate my tester is but thats what I got..)

The measurements I have managed to get are as follows:

CYLINDER: 69.72 - 70.02 mm
PISTON: 69.85 - 69.88 mm

(I did clean the piston)

(https://lh3.googleusercontent.com/-JLTNbyBf4uw/U49ehegZ-fI/AAAAAAAAB1g/G_9wna-lHDk/w487-h649-no/20140604_185612.jpg)(https://lh5.googleusercontent.com/-revxcS_VQ3Y/U49fQvi0LUI/AAAAAAAAB1s/LO3-Y1cFzIc/w487-h649-no/20140604_185619.jpg)
(https://lh6.googleusercontent.com/-u-dGRbZZ1ZQ/U49eZB4vz5I/AAAAAAAAB1U/8dVqPptkyus/w487-h649-no/20140604_185608.jpg)(https://lh3.googleusercontent.com/-uZVxJatyKsQ/U49eQdUZ32I/AAAAAAAAB1I/59RGfXsBKmk/w487-h649-no/20140604_185600.jpg)
(https://lh3.googleusercontent.com/-k5_Rua6MsRc/U49eFpbOAGI/AAAAAAAAB08/7hDZIKTKS0s/w487-h649-no/20140604_185545.jpg)(https://lh5.googleusercontent.com/--OX73aoPW_U/U49d9cmxHvI/AAAAAAAAB0w/zR1dQuYRGeo/w487-h649-no/20140604_185532.jpg)
(https://lh3.googleusercontent.com/-8ELjvTfou4s/U49dzG7oXZI/AAAAAAAAB0k/ddV4d-tR0e0/w487-h649-no/20140604_185525.jpg)


Thanks for your help!!

Title: Re: Kx250 1986 correct piston size for my engine, what to order??
Post by: Foxx4Beaver on June 05, 2014, 01:45:40 AM

I'm sure others will give their thoughts and opinions...but if it were me, I would re-plate the cylinder, new piston/rings/wrist pin/wrist pin bearing/circlips....throw those crusty old cylinder studs out and put in some crispy new ones...(but after you have lapped the cylinder and head to be sure they're both flat!), and a complete Cometic top end gasket kit.
Then you know everything is new and should last you a while providing you're good at keeping on top of your general maintenance.

Title: Re: Kx250 1986 correct piston size for my engine, what to order??
Post by: tracks on June 05, 2014, 07:54:22 AM

Thanks for your response, yes I agree thats what it does really need but I just want to get the bike running (understand it won't be as good as it could be) - it's just not really worth spending the money on. I'm prepared to put another £100ish into getting a new piston kit but after that I might as well sell it and buy something in a better state..

Title: Re: Kx250 1986 correct piston size for my engine, what to order??
Post by: bens87braap on June 05, 2014, 10:35:55 PM

I bet if u spent  300ish u wouldnt want to sell it ;)  just my 20 cents worth Id rather fix it then u no what u got and u will respect it more