this page: http://www.bacomatic.org/~dw/sixto/sixto-0.htm Sixto Bernal, one of the members of the Fordnatics mailing list, is building a 3.6" stroke 289 for 366 cubic inches. He ran into trouble getting it balanced - essentially, no shop he found in his area could do it. I figured I could. I did, but it was one of those "never again" things. Basically, Sixto's problem was by the time he trimmed the counterweights down so the pistons didn't slam into them at BDC, there wasn't enough counterweight to do the job. Sixto's crank has something like eight *pounds* of heavy metal and lead in it; the counterweights are essentially cast iron lattices filled with tungsten alloy and weld. I wouldn't want to do another like this, but I managed not only to balance it, but I balanced it to the stock 28oz damper and flexplate, which I thought was a major accomplishment.


As it arrived; several pounds of clay were required to keep the crank from hopping off the rollers. The crank had been stroked by Rigo Saltero in California; you can't tell in this photo, but he did an excellent job.



The other end; still more clay.



Marked places for the first batch of heavy metal, pilot drilling holes. The crank is so far out of balance I'm installing the maximum amount of heavy metal in each counterweight, which means inserting slugs of heavy metal radially.

Note wooden box that holds crank so it can't bend under the drill pressure.



Drilling holes for the first batch of heavy metal. All the counterweights will wind up being filled in the end, so I'm doing them all at once. Normally you'd fill the front and rear counterweights first, but since I'm pretty sure I'll need everything, I'm starting with the middle. If I wound up not needing much in the ends, having the weights inboard would reduce the load on the crankshaft. Alas, the crank needed all except the rearmost counterweight completely filled.



Getting ready to hammer in the heavy metal. Note "terraced" notches so drill could start square to crank. This all gets welded up later.



Testing, still a long way to go. The crank was probably on and off the machine fifteen times; each time the weights have to be removed and reinstalled in precisely the same places. It's a time-consuming job.



In progress; some heavy metal is welded over.



Cutting blocks of 5/8" cold rolled steel to add to middle counterweights, to get every last bit of mass possible.



Sawing blocks off at an angle for less grinding.



Profiled counterweight blocks, hot off the bench grinder.



Blocks have been welded on, welds ground down, blocks ground to clear the block and contoured to meet the rod throw, clearance hole drilled through to the crankshaft material, the crank has been drilled and tapped, the block has been counterbored for the bolt, and I'm running a grade 8 3/8" fine thread bolt in to help retain the block. I don't entirely trust welding steel to cast iron with the MIG welder; if one of the blocks were to come loose it would be catastrophic. The bolts got tightened to 45 ft-lb. Not much chance of anything coming loose; they're larger and stronger than the engine's 5/16" rod bolts.

Note the front counterweight has been entirely welded over all the heavy metal and steel plugs and the edges are squared, to get every last bit of mass possible on the OD. There has been some grinding on the front rod throw to take some weight off the pin side. You can see the #4 throw in the background; notice it has some weight that could have been removed if needed. Fortunately the back wasn't as far out of balance as the front. The SBF's imbalance is different on each end.



Laying some tape in an extra block - I didn't have any of the right size main bearings handy - to see if the extra metal welded to the crank would hit anything.



Unfortunately those are all the photos I have available. It took a set of lightweight wristpins to make it, but it finally balanced out!

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