1988 XC250 revival 2016

the 250 was a 240 all along. they were built to pass the fim laws and rebadged for the rest of the world

the 240 and 250 have same stroke all thru the years. if you bore the "240" you will arrive at the stock 250.
the skirt does more than stabilize piston, if you install the jug and piston and turn engine over looking thru the reed area...you will notice that you never see over the top of the piston. the fuel/air charge is drawn below the piston to the crank case, then thru the boost ports to the combustion chamber. if the skirt is any longer on the intake side, it will affect performance. the piston you bought is an unusual listing from wossner..

Can't argue with that. Didn't consider it really. Might that be what the "pockets" are for on the intake side of the piston? I could have the piston machined if its going to be an issue.

So if you don't see the whole top of the piston does that mean you see the bottom? For the fuel and air mix to get down there it must go up past the intake port correct?

I suspect this is a bit of aftermarket engineering. Those two large pockets (they look almost like ports but are milled out little wells) may be there to counter act the lengthening of the intake side piston skirt, which in my mind would make a stronger piston as well as one that could wick heat off into the cylinder better. Thoughts? I can't see why else they would exist.

my comment you quoted is pretty much true of all two strokes..there are other huskies and other two strokes that use these pockets. im not convinced these are a replacement piston for the 87-88 250.
you see, we arent aware of any option other than oem for this particular engine. all the big bores up to 88 are covered, and all the 250 bikes up to 86 are covered. the 87-88 has less bore and more stroke. same rod as other 250s, the 400, and 430..but pistons are hard to find. maybe wossner finally came up with one for this 250 but didnt get it quite right.
regardless, you will need the intake skirt matched to your old piston.

Oh I don't doubt you guys but now that the cylinder is at the machine shop I'm kinda in a panic situation, potentially making one big paper weight.

If the stroke between the 240 and 250 is the same what would make the pistons be so drastically different? I'm having a hard time finding a picture of a 240 let alone one of any engine components.

a 240 would be identical except for bore..same everything, well except the airbox decal.
i suppose you could always cut the skirt and chamfer the edge to match the old piston.
halls is a top notch place, hard to believe they would be wrong about the piston application.

Interesting. I'm still questioning why they engineered the different piston if everything else was basically the same. I'd say it was due to more fuel and air needed for the slightly larger 250 but if it ran the same carb that theory kinda goes out the window. Generally manufacturers love to use one part for everything.

As a "amateur" machinist (though I do run a portable align boring machine that cuts heavy equipment pin bores to .002 tolerance on diameter for money pretty regularly) I can only imagine how hard that would be but I have no doubt someone much smarter than I could likely make anything happen. I'd love to come up with a solution that ensures me years of smiles on the bike.

the 84 parts book only has 1 piston for cr wr and xc in 3 oversizes.

the 88 manual lists one piston for wr and xc as 250's with three oversizes and only one piston size for the 240. Its hard to tell what the difference is other than the bore size without having both side by side.

amazing.... why would they bother? the 240 was to ensure that even on full oversize, the engine met FIM size restrictions of 249 cc or such. I guess in competition a few cc is a psychological factor as much as the actual power difference. the American market loves its cc's

the 240 will likely be the "exact same motor" except smaller bore. one size smaller than the "250" std bore, at least thats how other years 240/250 bikes are. the only reason 240 bikes exist was to get around a rule concerning 250 class engines, so i was told here. not like its a different model or something.

what does that have to do with the 87-88 250 "stroker" bikes?

i can tell you kyle i have owned the same bike as yours since high school, where i had bought one as new..never started..great motor. last year i pulled the 250 out and have been running a 430 in it. but i miss that little 250. need to freshen it up...still has well over 200 psi and who knows how many hours on it..

hey, youre the one running a 400...

a 400 in a 87/88 WR 250 frame, who would do that lol
I am saving my mint 250 low hour stock bore for some day...

that mint 250 will run at least 200 hours on 40:1 klotz super techniplate

Holy longevity! Makes sense though, I have a 1997 Husqvarna 272XP chain saw that I'm sure has never been rebuilt and has likely more than 200 hours on it and it still runs flawlessly. My uncle rebuilds his saws a little more often but he makes his living with two Huskys on his sugar farm and works the hell outta his saws.

I'm really hoping I get this piston to work out, seems like if you have this bike you don't use it because of the piston dilemma and thats just not right. I'll mock up the top end before I machine the piston. I'd like to compare the original piston to the new one over the length of its travel as viewed though the ports.

I had a 240 from new...still trying to find where it went

thats not the case with me! im just afraid of piston fatigue with so many hours, i want to refresh the top end before something happens.. i have other huskies as well so i just pulled the motor till i get around to it. i love how the 87-88 250 bikes run.

So The Crank Shop called this morning with my bored and honed cylinder ready to be picked up.
I talked to a super helpful enginebuilder/machinist who said that the difference in the exhaust skirt wasn't really a concern unless I was looking for absolute top power. He verified the wrist pin height and placement were identical.
After looking over both new and old piston he said they could easily cut the pistons to be identical but he really didn't think its worth the added time or effort.

So I went home and put the top end together and rather sloppily threw what I needed to run the bike with on for a break in. The shop said to break it in under load at varying rpm ranges for about 20 minutes so thats what I did.

Started first kick and has since. (Provided I can get a solid kick on it, I'm a short guy)

Power seems great, engine seems smooth and doesn't take long to get into the snappy power band. I'm quite fresh to two stroke riding and I feel I have a bit to learn in terms of shift points etc etc not quite used to the sudden rush to redline it has.

Having never ridden the bike with any other piston so not sure how it would compare side by side and I was trying to play nicely so I didn't really get into it like I would usually. Someone with a stock XC come over, we can drag race up and down the mountain!

I still need to get the proper plug for it. It had a BR9ES in it when I got it which I know is standard gear for two strokes so should I be running something else?

I was also monitoring temps of the cylinder head and radiators periodically throughout the break in and the external temp of the cylinder head never exceeded 200 and radiator around 170 so I'd say I'm in the safe zone temp wise. Didn't think to measure pipe temp to give me a clue to combustion temps but it never felt unreasonably hot.

So there you have it. That Wossner piston WILL work if you need to oversize your stock 250 bore. I'll try to keep everyone posted on how it behaves and longevity.

run it in plenty before really working it and it will last longer. quality equipment. I give 3 full tanks of light running and lots of hot cold cycling working up to the power and shifting up gradually holding it on longer and longer letting it work in. u can usually feel its happy spot in the rev range slowly increase as it gets worn in. enjoy two fitties are nice

Thats what I figured, it will come with time. So far so good, I'll make sure to cycle it good this weekend, need to get more fuel and oil as well as some engine oil thats not 10w-40. (It was on hand for the time being and full synth motorcycle oil I might add)

I noticed my right hand fork seal that I just installed is leaking already. Good stuff. Probably ham fisted install error on my behalf.

Looking forward to this weekend to say the least, heres to hoping I get more than a weekend out of this top end!