Friend putting diff piston in Help Please

[720tobe]

hello, guys i have a buddy that is getting ready to rebuild the bike for the first time its a 05 yfz he was wanting to put a better piston in it,, he was wanting to make it a true 450 or better i read on the 06 crank to make it the 450 but he really doesnt want to swap out cranks so what about boaring it to a bigger piston,,didnt know how big you could go on the piston and not have to worry about heating issues or maching the cases... So pretty much the q's is what does he need to do to put a piston in his 05 and which piston to go with size and compression to go with.... I know he has the cam mod and filter plus slip on... thanks for you help guys i dont have a yfz or i could help him..

[720tobe]

Hello, can anyone help on this please.....

[Jim417mx]

yfz cylinder walls are thing enough as it is, boring would not be a safe option. If you look on ebay they sell new OEM piston/cylinder kits, and that is the reason, because they are rarely ever able to get bored. The best bet would be to go with a big bore kit.

[720tobe]

ok i read somewhere that you have to get your crank ballanced if you dont use the stock piston which doesnt make any sence to me but is this true... also would it be the same to re ring it and put the 06 crank in it probably save money that way unless the cylinders and piston isnt that much i fig he could pick up a crank somewhere for 150.00... thanks for your help..

[mxpimp2000]

chances are the nickle plate is worn and would need to be replated or just buy a new cylinder like i did. i went with a 13:1 wiseco std 95mm bore piston and it was a great mod. it might not gave me alotta power but it felt like it did,

now im going with the curtis sparks piston kit for this year. its a higher compression and more for race gas and racing applications.

my opinion id get a 12.5:1 95mm piston (still be able to run pump 93 gas) and replace or replate the cylinder. if u got the money get the 06 crank because odds are it will need a crank in the near future. JMO:)

[720tobe]

ok thanks guys ill let my buddy no what you all had to say i told hit he needs to do the 06 crank no the q's is what year crank will work in the 05 and which is the best stock crank or are they the same from 06 up

[mxpimp2000]

06+ are all same. keep in mind 06+ has a diff stroke and when ordering a piston the compression changes. for example:

04-05 13:1 piston=12.4:1 for a 06-08

sometimes people dont state what year there for they only say 04-08 because they dont know the compression differences. i learnt this after i bought mine and my piston was actually pushin less compression then i thought.

with the 06+newer crank and a new piston he will be one happy camper. that makes it a 449cc instead of the 439cc that it is now.

[720tobe]

ok so you have to run a 06 to 08 piston with the new crank if not the 04 05 has a higher compression would it be better to run the 04 05 piston with the 06 crank...

[mxpimp2000]

only thing diff is the compression by .5 as long as u dont go over 12.5:1 you can still run regular 93 gasoline

just get a 12:1 or 12.5:1 for a 06-08 unless he wants to run 93 mixed with 110 dont go over 12.5:1 compression

[720tobe]

ok cool guys thanks for the help....

[nicker71]

Leave the crank alone and a 96mm kit.gt thunder sells them. They are about the same compression as stock and very reliable. Makes it a true 450cc. Puts out good power. I race XC but I took it up to the dunes last year and when drag racing did very well with it. Ran the top end for 2 seasons and never had any problems with it. When I sold the bike it was still running strong.
Sure you can replace the crank and spend more money, but why??

[720tobe]

cool man is it a new jug and cylinder or just a press in to your old jug and how much does this setup cost....i got to get him up and running as i have no one to ride with...

[mxpimp2000]

Originally posted by 720tobe
cool man is it a new jug and cylinder or just a press in to your old jug and how much does this setup cost....i got to get him up and running as i have no one to ride with...

that complete kit is in the 400s comes with everything. because its a bigger bore 96mm u cant use stock cylinder. im sponsored by GTT for 2010 i thought about gettin that kit but its designed for xc racing and thats not my style lol :D