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piston seized??99 cr250r

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so,ive just spent the last few weeks putting my bike back together whenever i could sneak an hour or so in.new sprockets,chain and top end.i was trying to start it this morning for the first time.i tryed several different ways,fuel on,choke on.fuel off,choke off.throttle open,throttle closed etc.anyway i eventualy got it to turn over but it cut out and the kickstater seized.:moon::foul:so i take it i seized the piston.if so, is it fuct and why did this happen??what can i do to insure this doesnt happen again.what is the reccommened procdeure for start up after a rebuild?

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only way to find out is to tear it down. Seems you may have dropped something in the motor or installed something improperly.

How did the bike run before the rebuild?

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sounds like something wasnt put together right. No way the piston seized up. gonna have to pop the jog off and look at it.

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so,ive just spent the last few weeks putting my bike back together whenever i could sneak an hour or so in.new sprockets,chain and top end.i was trying to start it this morning for the first time.i tryed several different ways,fuel on,choke on.fuel off,choke off.throttle open,throttle closed etc.anyway i eventualy got it to turn over but it cut out and the kickstater seized.:moon::foul:so i take it i seized the piston.if so, is it fuct and why did this happen??what can i do to insure this doesnt happen again.what is the reccommened procdeure for start up after a rebuild?

You sure you did not put the piston in backwards? Sounds like the rings hung up?

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my buddy did the topend on his 02 cr250 and put the rings on upside down.both of them!and he didn't even check them before installing them on the piston so putting them both on that way....anyway the bike ran for about 2 minute before it died.lost all compression.we took it apart found the problem.the rings were stuck in the ring lands but we were able to get them out and off the piston.i would have replaced the piston and rings but he's a tightwad and we lightly touched up the parts with 300 grit emory cloth,put it back together correctly and it runs fine. we even used the same head and base gasket.will it last? i don't know.so check your rings at the gap for the "IT" marks.if they are up you have a different issue.your year bike wont run with the piston in backwards i'm pretty sure.it has the same piston as my 01 cr250 and the intake side is cutout at the bottom of the skirt.if you did put the piston on backwards i imagine the ring might pop out and hang in the exhaust port.since it barely ran you might not have too much damage.be thankful it not a 4stroke and seized$$$$$$$$hope this helps.:moon:

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I got a wiseco piston and the rings have no indication on what way is up ?

Only way to find out is take it apart... Keep us updated.

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ok,im feeling like a right gobshite now.i didnt know the ring could be put in upside down.this is my first bike n im not exactly mechanicaly minded.kinda winging it n using a haynes manual.its a wossner piston with only one ring.whats the difference with one,two rings.ill strip it down within the next few days and update.btw i put the jug back on about two evenings ago so im thinking the oil that i put on the piston drained away:bonk:hope its not as bad as i think its gonna be...

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only some rings have an "this side goes up" mark. If it has no mark , it can go in either way

piston definitely has to go in the right way, there should be a mark or arrow indicating front, check instructions for the piston.

one ring piston has more top end power, slightly less low end power, suited for mx racing. One ring wears faster than 2. No big difference between one and two ring. I believe the wossner piston is forged, which is good since it's more durable than cast pistons.

Haynes manual should be good enough, follow each step carefully and ask questions on this board if unsure on any step

If this is your 1st top end, you could ask somebody who has worked on engines to help. If nobody around, the folks on this board will help, if you take it one step at a time and post photos. Read the old top end how-to posts.

oil draining away would not be the problem

how many minutes or seconds did it run before it quit?

did it make any unsual noise while it did run?

some other possible problems to check / measure:

- measure piston to cylinder clearance withn feeler gauge at the bottom of the piston, front of back side. Clearance spec given per Wossner instructions, should be something like 0.0015" or 0.002" minimum. If not enough clearance, piston will multi-point sieze as it warms up a minute or so after engine started

- install rings in cylinder without the piston and measure end gap. Gap should be at least 0.012". If not enough gap, ring will expand into ports and snag as engine is warmed up

- was engine running normally or was it reving high? An air leak will lean mixture and cause engine to rev even with throttle closed.

...alex

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the piston was put in with the arrow facing backwards,towards the carb not the exhaust port.as for clearence ill have to check that when im stripping down.all should be fine.i had the previous owner rebuilb the bike with me there before buying it.hes a friend and a top rider here in ireland on gp bikes so im sure he can spare a few days over crimbo to give me hand.we replaced the crank[hotrods]and piston that time and the jug is fairly new.think its recoated.but i could be wrong about that.i put the same size piston in as before which is 66.34mm A.ill stiip it down and post some photos,cheers lads,thanks for getting back to me.the only reply i got on an irish forum was to try jumpstarting the bike in gear.not the brightist idea i think:bonk::moon:

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mken, any update?

with piston backwards, the ends of the rings probably snagged on a port and maybe gouged the cylinder. no worries, can be fixed and replated for ~$200 by shops that do cylinder replating. here in the states, folks recommend a company called Millenium Technologies

if it looks like metal debris was created, you should flush out bottom end by removing engine filling bottom end with kerosene/diesel fuel and pour out quickly. Or to be 100% safe, split cases to clean debris. With a "dry" crankcase, you should to pour 20-30cc 2 stroke oil into bottom end before putting cylinder back on.

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i havent had a chance but ill be starting either tonight or tomo morning so ill update with some pics then.i picked up a new piston n gasket kit and im hoping theres no serious damage but we ill see.the new piston, Namuru has an IN mark.wouldnt life be a whole lot eassier for us beginners if manufacturers used the same symbols and marks.ah well,live n learn!!!!

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MKEN, welcome to TT!:moon: You mentioned that the oil you put on your piston has drained away? I assemble mine dry, only oiling the wrist pin/bearing assembley. Good luck and keep us updated on your findings. Larry

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MKEN, welcome to TT!:moon: You mentioned that the oil you put on your piston has drained away? I assemble mine dry, only oiling the wrist pin/bearing assembley. Good luck and keep us updated on your findings. Larry

cheers ive been lurking around a while just trying to soak up the info.great site from what i have seen.anyway down to buisness

well i stripped it down n its not as bad as ithought.will it require re coating or could i use it as is.there wasnt any bits of metal on the crank or around it but i think if its not to hard ill try flush out the case.how do i go about this.btw whats the big bolt and the case on the side of the jug for?

IMG_6634Small.jpgIMG_6642.jpgIMG_6635Small.jpg

Edited by mken

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To wash out the bottom end you have to take it out of the bike. Then tilt it over a trash can or you can hold it upside down over the can. Then you could use a can of 2+2 carb cleaner or something and spary it in the crank case and let it drain out and repeat this about 3 times and tilt it back over. Take a flashlight and look between the crank and see if anything. By the way it looks there should really be much down there so you should be fine.

How much of an edge is there on the scratch? You will have to try to get that off the cylinder some how. either a hone or you can use acid to eat that off the walls. But you gotta do something with it.

Also the big bolt you are taking about is the cover for the powervalve assembly

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cool,so you think if i just take the edge off it will be fine and doesnt need to be recoated???

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If it got into the bore of the cylinder you will have to get the cylinder redone. From the pics I cant really see how bad it is thats why you need to see if you can get the stuff off to see the acual cylinder wall

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