I bought a used 421 cub (whole motor) that was running with no issues. I pulled it apart, just for my own knowledge. Found a junk chinese crank, and only about 3 threads of the head studs were sticking out of the top of the head. Bought a new crank, seals, gaskets, and some extended head studs and put it all back together. The extended studs are for a pro design head so they are actually a little long for mine (chariot head). So i put the copper washers on the bottom plus two lock washers on top so i could get the nuts to tighten down. I had to use regular flange nuts cause the studs are too long for the acorn nuts. When i filled it up with coolant it started oozing out of all the head studs. My question is do the studs go down into a cub cylinder farther? I have a friend that runs a chariot head on a stock cylinder motor and his stock head studs work fine. I tried going back to the stock studs but i cant get enough threads to stick up out the top of the head. Are the chariot heads designed to work with the stock studs? Any help or info is appreciated.