You do not have to thread the shaft. Millions of 235s were produced and many are still running with the balancer just pressed on as far as it will go. Hint: if the balancer is from another engine, make certain the crank groove lines up with the water pump and generator (or alternator). You can move the generator/alternator bracket slightly for alignment, but you can not move the water pump. Second hint: get the repair sleeve for the balancer and install it. Rock Auto sells them. The groove worn in the balancer's shaft (even if polished smooth) will mess up your new seal...sometimes pretty quickly. The repair sleeve makes the shaft work like new. As for installing the new seal, I just use a wooden block and a small hammer and go slowly so as to get the seal in straight when I do it this way. Good luck!
