Im new here so sorry if this is to long. my 250x chain keeps jumping off. I cracked my stock swing arm around the carrier and thought that was the problem. I replaced swing arm with new 2inch exted burgards but after about 10 mins hard riden on track the chain loosens and jumps of rear chainwheel ANY HELP GREATLY APPRECIATED

 

make sure the axle carrier is tight also adjust the chain to allow 1-1/2 inches of free play with the rider sitting on the bike. Also your chain could also be bad. Check to see if it moves alot side to side. if so replace it.

 

Sounds like a worn out(stretched) chain. I would go out and buy a chain and sprockets.

 

I had the same problem with my 250x and the problem was that the chain kept getting loose after 5 minutes after I tightened it.Look on the left side of the X and the bold that holds the swingarm on and it is atached to the frame,well see if that bolt is loose or if the frame around it is cracked,if so tighten the bolt or take it to a welder and they will fix the frame right up.If that is not the problem mark the carrier and the swingarm on the same spot with a pencil and go ride for 5 minutes and see if the carrier slid any.And if none of this is the problem then get a new chain.

88 250X,AC nerfbars,grab bar,Renthal bars and grips,Kehien carb,holshots,K&N filter and 300EX plastic

 

I have a new chain new front and rear sprokets and there are no cracks in frame also the bolt is tight! Im at a loss here. Unless it has something to do with the little thing that holds the front sproket on it looks a little worn and my front sproket moves side to side quit a bit, is this normal thanks alot!!!

 

what about the chain rollers on the frame. are they still there? if so in good shape? those rollers believe it or not make a big difference

 

My X had a similar problem, and being a meathead I ignored it. Bad idea, after DNFing in two races and finally throwing the chain and unknowingly cracking the case (and wasting the motor) while trail riding, I finally realized the culprit was an oblonged swingarm pivot bolt hole in the frame. I machined a special washer and welded it to the frame to properly support the bolt. And make sure its tight.

 

The sprocket is supposed to be a little wobly.The problem may be that the rear sprocket is loose.The only way to tell is if the chain is not on it.Also see if you have good teeth on the sprockets.Behind that bolt I told you about there is a rubber chain guide the chain goes over.Make sure it is full size and not worn down.Get back to me if none of this is the problem.

 

did you use the stock bearing carrier....
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you may have a worn cam for the chain adjustment.....(the off centre bit round the bearings).....

if you tighten the chain adjusters and it keeps moving forward slackening the chain....this maybe the prob

you can build it up

or more often its better to replace the whole bearing carrier (either way, make sure you go easy on the alloy bearing carrier, they don't like being hit hard!)

check for wear on the engine casing round the front sprcoket.....if it has been doing it for a while check the condition of the chain.....constant beating of the chain can cause it it crack and shatter

if you are taking the back end appart

i would recommend fresh bearings,seals,chain,sprocket, once you are confident you have solved the prob.....

i have got my bearing carrier built up and, just got my rear axle built up.....the bearings were spining on the axle.....for me its cheaper than importing stuff from the US......

 

You have gotten many ideas on how a chain can come off. Don't just check one, but check them all.
1. woren out chain
2. woren out sprokets
3. woren out rear bearing
3. chain not adjusted corretly
4. swingarm pivot bolt lose
5. swingarm pivot bolt hole oval shaped
6. woren out swingarm bearing
7. sprokets not lined up
8. output shaft bearing in case bad
9. skid plate pushing chain off
This is not a comeplete list, but it is a listing of what has been talked about. I don't think that I forgot any. But, if I did add it to the list.