402 Big-Block Rebuild, Part 3 - 1967 Chevrolet Chevelle SS

Tech - Real World Street Big-Block, Part 3

Patrick Hill Jan 23, 2014 0 Comment(s)
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402 Short Block Crank 2/37

13 With the caps secured, Jason tapped the crank flange to get it aligned properly for checking the crank thrust.

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14 After you've torqued the main caps down, you should be able to spin the crank freely with your hand. If the crank doesn't turn easily, then something's not right, and you need to take everything back apart and check all your clearances again.

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15 Using a dial indicator, Jason moves the crank back and forth to see how much thrust there is. The acceptable range for crankshaft thrust is .003-.008-inches.

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16 Next we get to install our new Lunati mechanical flat tappet cam, part no. 30110512. It specs out at .550 int./.570-inch exh. lift (with a 1.7 ratio rocker), 238/248 duration at .050-inch, and a lobe separation of 112-degrees. Its optimal rpm range is 2,400-6,800 rpm, with a fair idle, and will work well with our 3.73 gears and projected compression near 10:1. It needs a minimum of a 2,500 stall converter, which we'll have once we do the 4L80E conversion to the car.

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17 Before installing the cam, the journals were coated with AMSOIL engine assembly lube, and the lobes with the included moly paste. You don't want to slather the lobes with paste like you were laying bricks, but want enough coverage to protect them during initial start up until the oil pressure comes up before break-in.

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18 For the timing set, we went with Lunati's billet double-roller timing chain, part no. 95510, featuring a nine-way adjustable crank sprocket for a wide range of tuning options. We also got Lunati's cam bolt lock plate kit, so we wouldn't have to worry about our cam bolts coming loose.

402 Short Block Lunati 8/37

19 With the cam installed, it was time to get our rods ready for mating with their pistons. Our Lunati rods (part no. 70461352) are a 4340 forged steel, H-beam design featuring bushed ends, and cap screw retained caps. Tey are also shot peened and Magnafluxed. Length is stock 402 6.135-inches. These rods will handle just about anything we can throw at our big-block.

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20 Our Lunati rod/Wiseco piston combo utilizes a free floating in design, with the pins retained by spiral locks on each end. To properly install them once the pins are in place, spread the lock apart, then feed it into the piston's lock groove in a wrap-around method. Not hard to do, but it does require a bit of patience. We lubed the pins up before installing them in the pistons and rods.

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21 Time to fit our rings. Wiseco sent us a set of file-fit moly rings for our forged slugs, giving us the ability to get the ring gaps perfectly dialed in, a must for a performance application. To do this, you'll need a ring filer, feeler gauge, and a square. The first step is to get the ring squarely in the cylinder.

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22 Then, using the feeler gauge, measure the gap between the ring ends. Jason likes to leave four thousandths of an inch per inch of bore when setting ring gap. So, in our case, the goal is a .018-inch gap.

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23 Using the ring filer, Jason gently files away a slight amount of ring material, then sets it back in the bore, measures the gap again, and repeats the filing process until he has the desired result. This process is a lot like carpentry, measure twice, cut once. If you file away too much ring material, the gaps will be too big, causing a compression leak in the cylinder and killing performance.

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24 With the ring gaps set, they could be installed on the pistons. Jason advises against using a ring spreader, as they typically overstress and break the rings when used. He installs rings by winding them around the piston into their grooves. First is the oil control ring, followed by the two compression rings. Once installed, clock the individual compression ring gaps 180-degrees apart, with the gap for the oil control ring between the two.


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