yz 250 piston in a 250r engine

[holeshot19]

once heard of people useing a yz piston in a 250r engine just wondering if anyone has used this:mad:

[Juggalo]

i heard of people doin that for the LT250 motor btu not the honda R. maybe some people do it tho.

[Chanman420q]

maybe a CR250R piston in a 250R...

[fourtrax400ex]

one of my friend said that he use a yz250 piston in his 88 250r, i dont remember the size of piston, but i know that it can be done but there other mod to do to make it works

[Chanman420q]

whats the advantage of using a yz piston over a normal trx piston

[ridered86]

Originally posted by Chanman420q
whats the advantage of using a yz piston over a normal trx piston

thatys what i wanna know:huh

[holeshot19]

susposably the yz pistom is a shade bigger than the .080 trx piston in 87 up cly so u have one more bore insteve of resleaving . i know that loron duncan sell diferent thickness spacer plates for different pistons

[Honda52]

Dont put a yz piston in your R. my cuz did it and it ran like garbage. it was sooo bad. he got a new cylinder and a night and day difference. it had a lot more power with the stock piston in it

[MOUSE]

my friend has this done and it kinda according to him makes it act like a stroked motor yes you have to have a different sized plate in it but i cant remember what the size is right now, and there was a lot of difference in his after this was done. :eek2: it runs like a scalded dog

[fourtrax400ex]

the yz piston is bigger than the R, you need a spacer at the bottom of the sleeve i think, if you dont have the right spacer, it will not run good. so maybe that's what honda52 talk about, probably not the good spacer height. i can tell you that the 250r of my friend run like a bullet, this thing pull very hard, tons of low mid power(i can said more than a stock 400ex or other similar four stroke). if you like to do it i can ask him what piston use and what spacer.

[holeshot19]

thanks i would like to know. i ordered a 2mm spacer from duncan once and tryed to use it in a 86 cly with a long rod and it had way to much compression like 250 psi and leney at duncan said thats way 2 much so i used a 4.5 mm plate but i have several 87 up cly that are on the last bore .080 and need new sleves and allways wondered about the yz thing:eek2:

[MOUSE]

i want to say that it needs to be a yz250 piston with a 8 mm plate but dont take my word for it. call someone to be sure but i think thats what he has in his. also there might be something else to go along with the piston and plate to make all of it come together in harmony but there again im not sure hope it helps

[OutlawEX]

I woudlnt risk it:confused2

[mxracer111]

i am a 4 stroke guy myself.... but if i am correct.... Curtis Sparks uses a YZ250 piston in all of his 265 national R motors with that really thin spacer plate....its about an eighth inch thick or so....those motors really scream.... but there is also porting, headwork, carb. etc. they all must work together

[darrell43031]

i agree i wouldn't do it. i once had a mechanic tell me that there is no stronger piston than a honda piston. all aftermarket piston's are weaker than a stock one. which makes since cause i personaly have never heard of any body i know of have there stock honda piston burn out on em. but i have a friend with a 300ex that rebuilt his bike 3 times in one year cause his weisco piston kept burning a hole in the top of the piston. he was running straight cam2 in it. i run straight cam2 in my 300 from time to time and have never had a problem

[airheadedduner]

Originally posted by darrell43031
i agree i wouldn't do it. i once had a mechanic tell me that there is no stronger piston than a honda piston. all aftermarket piston's are weaker than a stock one.
ART makes stock pistons and the PRO-X pistons. So they are the same. Wiseco's are forged, much stronger then the stock cast.


I think he ment better not stronger.

[fourtrax400ex]

holeshot19, i talk to my friend about his yz piston, he said that you need a yz250 piston (year 83 to 87, its suppose to be the same, he use a 87 i think) the maximum oversize of 250r are 68mm i think, the yz piston is 69 or 70mm, you dont take the standard bore, i think its the last oversize. you need a spacer at the bottom of the cyl. of 1/4 inch, (approx 7-8mm like Mouse said) because the 250r piston is shorter than the YZ, but he dont use gasket on the bottom, he use silicone gasket on the two side of the spacer, if you put gasket, you need a tinner spacer, 7/32 inch he said. you have to check if you can bore as high, i think that the R dont have all the same sleeve thickness. with this setup he has about 180lbs of compression. more than that you will lose performance. he also have worked is head to put an o-ring, the top gasket has tendance to fail. it run with this since 1year with no problem and it pull very hard. perhaps, if you ride a lot i dont think this setup is for you, the motor run hotter(thin sleeve) but if you just doing drag racing, or something like that, it can be done. hope it helps!!!

[holeshot19]

i looked up 83-87 yz pistons and they start at 68mm and thats the last bore size of 87 up r clys but they had 68.25 68.5,68.75, and such i have hear people tyrying to use a 86 trx piston on 68.5 and the cly cracking wondering if the 68.25 yz work i looked threw my duncan catalog and they list 2mm-3mm-4.5 mm spacerer plates for trx and yz pistons but dosest say what year.