GM balanced engine Part II

[John A. Marker]

Okay.....got the new flexplate this morning and took it over to Ed's to have the crank balanced. Carlos had everything setup and we bolted on the new flexplate and started up the machine. This is quite a setup. It is computerized and has a screen that shows two circles divided up in about 10 degree segments. (The segments are a guess on my part). We spun the crank at 530 RPM and the weight difference is displayed on the right and left of the upper screen and the circles now have a red dot to indicate the place of improper weight. The circle to the left is the front of the crank and the right circle is the rear of the crank. This is an internally balanced 350 and you remove weight from the crank. You do need the flexplate and the harmonic dampener attached to the crank since they are part of the rotating mass. The flex plate that I brought in had weights welded to the plate. The first spin indicated that the front of the crank was at 28.4 grams and the rear was at 10.8. Some of this difference could be the flexplate and dampener. Carlos told me that NASCAR standards are 3.0grams front and rear. There is a red dot in both circles in different locations. He turned the crank by hand until the solid line on the screen lined up with the red dot. This positions the drill vertically over the crank. The drill is on a rail that slides over the crank and he positions the drill at the front of the crank and drills out some material. Spins the crank again, lines up red dot and drills again. Spins again and drills again. This went back and forth from the front of the crank to the rear of the crank. Until the front of the crank was at .01 grams and the rear was at .38 grams. This is were the experience comes in, knowing how much to take off when drilling to get things as close as you can. Carlos said that he balances a crank to within .5 grams front to rear because that is how he learned to do it. That exceedes the NASCAR specifications and I am happy with the results. By the way, the flexplate and the dampener are GM! It was very interesting to be able to watch a craftsman at work and be able to ask questions as the balance progressed. I learned a lot today. At the initial spin at 530 RPM you could tell there was a slight vibration. You are only riding on two journals, front and read. After the balance, spun the crank up to 750 RPM and it was as smooth as could be. A expernally balanced engine (like a 400 block) would have the same set up, dampener, crank and flexplate or flywheel. But in case they would remove weight from the dampener and flexplate. For those in the greater San Francisco Bay area, Ed's is the place to go. Signature soooooon to be UPDATED....