IT 250J 4th gear probs

[gamma500]

i have an IT250J motor in an imported yamoto quad(im in aust) i have had the IT since about 1986,it keeps stufffing up 4th gear selector,keeps wearing side with small lugs,split cases and replaced once with second hand 1(couldnt locate a new 1),new spacers and circlips lasted about 20min and started doing it again,split cases again and welded up old 1 got it looking as good as i could,same thing happened,i was using and followed clymer manual,when i first split case there was a splined washer over left end of front shaft against bearing in case but in manual it shows a normal washer not splined(local yam deal could find out what was supp to be there)also when i put the motor in the quad i had to change from 520 to 426 chain to suit back sprocket,only sprocket i could get for fron was 13th 426 with a larger centre,it not that very large in diameter so had to slightly space sprocket to stop chain from rubbing,wondering if this might of took to much play out of rear shaft for selectors to work prob,thanks

[D tom]

Those shift dogs need to be nearly perfect if they are even slightly worn or rounded it will kick out. Check the shift forks for wear or bent.All the spacers and washers need to be perfect .I dont think the sprocket will effect it.