[danthefamilyman]

I have been asked several times how the flywheel was balanced. I wanted to post pictures of the process but did not take any pictures when I did it (I was having too much fun) so I guess I will just have to describe it.

It is based on the fact that two rods at 90 degree angles to each other (one on top of the other) have very, very little contact area and thus very low rolling resistance, allowing for very fine static balancing.

How it was done:
During the machining of the flywheel, while it was still in the lathe, the center hole of the flywheel was set up to within .0001 of the crankshaft bore. This allowed the center hole of the flywheel to be used as true dead center.
I then machined a shaft 8" long with a .0015 taper from one end to the other and sized it so that it would be a slight press fit when inserted into the flywheel center hole. So, I now have a fly wheel with a shaft sticking through the center of it (shaft is sticking out of both sides)

Next: I placed two pcs of 3/4" Thompson Rod (62 Rockwell C scale -case hardened,) on steel risers about 6" apart from each other that alllowed the flywheel and shaft to be set on them and rotate until the heavy side was on the bottom. Using a machinist level I adjusted the two pcs of Thompson rod until they were level with each other.

Then:
I placed the flywheel and shaft on the Thompson Rods and allowed the flywheel to rotate until the heavy point was down. I then made a hanging wire pointer out of brass wire that hung from the tapered flywheel shaft. The wires point, pointed to the place on the flywheel that I was to drill a 1/2" diameter hole in the flywheel to remove material.

This process was repeated 8 or 10 times until the flywheel no longer rotated when placed on the two pcs of Thompson rod. In fact at the end of the process I could get the flywheel to rotate either direction just by blowing on it. I say it was within a quarter of an ounce, but in fact it was probably much closer than that.

This is the simple explaination of how it worked, there is much more to it.
The surface finish of the rods are important, the taper of the flywheel shaft is important, accurate machining and good dial / digital indicators can affect the results. I used Thompson Rods because they are very hard and have a good surface finish, I used Steel as the flywheel shaft and polished it before I used it.

How did I know how deep to drill the holes in the flywheel?
I machined a 1/2" diameter shaft of cast iron and made various lenghts of them. I would attach them to the top of the flywheel at the pitch diameter that the hole would be drilled. The length of these shafts would then be the depth of the hole that would be drilled into the flywheel.
I did one hole at a time, because as I would drill each hole location of the next 'heavy spot' would change.

It ended up with five 1/2" holes drilled into the flywheel. hole number five was only about 3/4 of an inch deep. It took 3 or 4 shots at the final hole (each one just a fraction deeper) before the flywheel no longer moved when supported between the Thompson Rods.

This was a modification of what an old journeyman machinist taught me when I was serving my apprenticeship. We used to have to balance our grinding wheels on our surface grinder before using them so that the wheel balance would not leave marks on the tools and dies we were building.

I hope this helps explain what I did. I wish now that I had taken pictures. It sure worked out well...there is no flywheel vibration at all engine speeds.

Thanks,
-Dan-