First, is it a steel crank or cast crank 340? The steel crank motor is supposed to have a neutral balancer (no notch or extra weight) and a neutral converter (no welded on weights). The cast crank 340 is just the opposite. It is supposed to have a balancer with either a wide grove cut out, or an extra weight just behind the crank pulley. A blind man could see it, so there'll be no question. Also, the cast crank converter will have weights welded on the side where the flexplate bolts on. Again, blind man stuff. If one type balancer converter or both is used on another type crank, it will vibrate like a sumbitch. You can tell whether you have a cast or steel crank easily. Look at the flexplate flange stickin out the back of the engine. Rotate the crank until you can see the "parting line". This is the line that runs the entire length of the crank where it was either cast or forged. For a cast crank, it will be almost pencil tip thin. For a forged crank it will be much wider.....more on the order of 1/2" wide or possibly wider. Insert the blind man comment here once more. Not bein a smartass about that....but it is just that obvious when you know what to look for. Lastly.....and this is the beeotch. Sometimes you cannot tell which type crank you have from the crank flange. In that case, you will have to drop the oil pan to find out. If you have to do that, simply look at the parting line on the side of a rod throw for the parting line. If you have trouble, post up some pice and we can help.
