1985 yz250 chain tension problems

I bought a 1985 yz250 of a guy last weekend, i got it home fixed the spark issue and about 30 kicks later away i went. now it runs OK.The biggest problem is that the chain seems to get really tight when i ride it. last night i was ripping around and found my chain to have tightened its self during the ride. I brought it home adjusted it to my liking (about 2 inches of play) drove it for about 5 km until i stopped to wait for my dad to catch up on the ttr :lol: As he was coming up he stopped and picked up the chain roller that fell of my bike. I wasn't to surprised as it was pretty rotten but when i checked my chain it was tighter than ever. im not sure where to go from here this would be the third time its tightened its self. what should i do?

heres some pictures

And il get some better ones tonight


I notice this side has that square bracket thing on the swingarm


And this side does not



Edited by Hutch1

That square bracket thing is the adjustment scale (axle block) thats missing.How are your swingarm pivot bearrings? Those adjustment blocks look way too far out and cobbled up with crap hardware. Get some pics looking down on your adjuster setup and that might help. I suspect that washer (if riding lopsided or on the ridge of the swingarm) is not allowing proper adjustment to be maintained. Use a sharpie to draw lines on the bolts and their corresponding surfaces to determine whats moving. And after each attempt at fixing, assume its still moving and check it after a kilometer. A tight chain is going to either smoke a tranny bearring (at a minimum)or snap and probably damage your engine case. Assume its gonna move til you get the stock hardware and get it fixed before its a pile of junk in the corner of the garage not worth fixing.

Edited by ickfinger

I have had this exact issue. Chain would get scary tight. Because there was no other culprits, I swapped the chain out with a new one, problem was solved. *Shrug* I dunno man. Try a new chain. Get an O-ring chain if you don't run one already. You'll thank me later.

i have not yet checked the swing arm bearings only the wheels and brakes. I'l have to pull it apart this weekend. Or start tonight if I get bored.

Here is some better quality pictures.




Changing the oil, its not leaking


Also what is this spring on the cable taped to the frame in the third picture? It is attached to the shock adjuster and I'm not sure where it is supposed to be.

I would start with the chain being @#$%. Looks like your driven sprocket is trashed too. I bet the counter shaft or the drive gear is nasty, doesn't look good in the pictures. Better jump on this before it takes out your case. You have a nice bike, don't bust it.

the only thing I could think of that may cause your chain to tighten, maybe it is getting hot, maybe dry? Those chains are just nasty, and you are due for the whole set. As for the axle blocks for adjusting, don't think your bike had them. I would sure put a very heavy washer on the right side of the axle under the nut. Make sure the edges of the washer don't get hung up on the ribs of the swing arm. Looks like you are about out of adjustment anyway. Rule of thumb is 3 fingers under the chain just behind the slider on the top of the swing arm.

Ask these guys any question you have. Lots of info here. Tap into it!!

Nice bike, have fun!

That chain looks too big for the sprocket. The spring is for a 1 year only BASS, (brakes actuated suspension system) which lowers shock compression during braking.

Ok thanks for the replys. I have new front and rear wheel bearing on order. should be in tomorrow. Going to examine the swing arm bearings this weekend, change fork oil replace tranny oil.

and now i'll have to order some sprokets. i sure hope this fixes it :) cant wait to ride it again. Also i checked the compression and it was at 130 psi cold is this normal? I was thinking it was a little low but im not sure

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