As we have been discussing deck clearance and stroke lately, there seems to be some need to explain offset grinding. This method can be used to get lots more stroke from an engine, or just a little to get a zero deck. It takes extra time to setup a crank lathe to do this, so make sure your machinist understands what you want and knows how to get you there. If you remove almost all the metal from the inside of the throw when crank grinding, the stroke can be increased by the amont removed from the rod journal. As an example, most 390s have the piston 010 down the bore when assembled (L2291Fs, TRW). If you are going to turn the crank 010 on the rods, the lathe would be set @ 1.892 throw. If instead you set it for 1.879, the lathe will grind you a crank with 3.794 stroke. The new center point on the rod journal also has the piston 005 closer to the top of the bore. Fortunately for us, the FE/FT series has large journals (2.438) and gives lots of room to work. I'll write more later. DF

 

Thanks, df. How much throw/stroke can you safely add through offset grinding?

karlsd a/k/a "ksd"
69 F100 Explorer 360/C6

 

How far can you go ? How much stroke can be obtained is dependant on how much metal you grind off. There are several rod options, 300 Ford 6, 225 slant 6 chrysler, 351M/400 ford, and afetrmarket rods intended for a big chevy. If one starts with a 390 crank with std 2.438 rod journals, a four inch crank is easy. Here is a build that I rather like- set the lathe for 2 inches of throw (4 inch stroke). cut the rod journals to a finished diameter of 2.200, normal big chevy size. Use Lunati 'pro-mod' connecting rods in a 6.536 length. The small end of the rod will need to be bushed down from the .990 chevy size to .975 FE pin size. The big end of the rod will need to be narrowed to FE size (width), use normal clevite 77 chevy bearings, with a heavy chamfer on the outsides. For pistons, use a 410 style piston. These will protrude above the decks and need a light cut. A 390 with this crank and 060 over is an easy 421 inches. Sometimes the oil holes are too close to the edge of the journal when finished, try to start with a crank that is not drilled sloppy. The closer together your oil holes are at the start the better. If yours are too far out, grind the passage over toward the center of where the bearing sits and then weld over the outside of the hole and re-dress the rod journals- your machinist will know. If you are really brave you can go 080 over and use L2303F or L2245F 428 pistons. Have fun ! DF

 

When y'all are going crazy on the crank lathe, lets be careful we don't make any very exspensive junk. I wouldn't try to go any more than 4.030 on a 390 crank. If you have a 410/428 crank I have seen them ground to 4.125 using 2.311 journals and 351M/400 rods. I have also seen an attempt to get a 428 crank to 4.210 stroke with a 2.200 rod journal. In theory this works great, in practice the inside of the cut breaks through the oil passage from the main to the rods- if there is a way to fix that I don't know what it is. So if it were my stuff 4.030 would be the max for a 390 crank and 4.125 for a 410/428 crank. Keep in mind Scat sells billet FE 4.125 cranks ( if you are made of money) and says they will be releasing 4.125 castings soon. I have seen their chevy cranks for the 383 strokers and would consider getting one when the castings come out to the market. DF