Welcome back to our real world street big-block build. If you're just reading about this for the first time, we're rebuilding the 402 Rat that was between the fenders of our rerstored '67 Chevelle when completed by the pros at Auto Metal Direct (AMD) and Craig Hopkins in the AMD Installation Center. The engine had been given a quick teardown and refresh to make sure it was reliable and would move the classic SS396 at idle for shows and events. Now that the car's trailer queen life is over, we needed to tear the 402 apart and get it ready for street/strip duty.
All of our parts are back from the machine shop, and it's time to assemble them. In this installment, we're just going to cover the assembly of the short-block, so we can go a little more in-depth on stuff to better help the novice engine builder out there. In the next installment, we'll cover the assembly of the top end, with special attention being paid to the break-in of our flat tappet camshaft.
For now, let's get our foundation put together.
Before we arrived, Jason had already cleaned the block and given it a fresh coat of high-temp Plasti-Kote Chevy Orange engine paint. This will ensure the engine still looks the part of a stock resto at a glance. The first order of business was installing our cam bearings. This requires a special tool so the bearings are installed squarely in the cam journals, and installed in each journal all the way.
2 On '67-up big-blocks, all of the cam bearings have holes in them that must be aligned exactly with these holes in the main journals. Oil feeds first through the mains, then to the cam in a big-block. If these holes aren't aligned, the cam bearings, and (after that) top of the engine will be starved for oil.
3 Before installing freeze plugs, Jason likes to use a thin layer of gasket shellac compound to help seal around the plugs.
4 Next up is installing the plugs in the oil galley for the cam bearings. Jason likes to drill a small bleeder hole in the front plugs (there's a pair at the back of the block too) to help keep any air in the oil passage bled out so the oil flows freely. Another benefit to this is squirting an extra amount of oil onto the timing chain to help keep it lubed properly.
5 Moving downward, the main galley plugs were installed. These were holes left from when the block was machined after casting. Jason uses shellac on the threads for sealing on these too.
6 To add strength to our two-bolt main bottom end, we went with ARP main studs to keep the caps secure. The studs are just hand tightened in at this stage, they'll be fully tightened once the caps are installed and everything is torqued down the first time. Over tightening them now can add stress to the block, and lead to over-torquing/failure of the studs. For those wondering why we didn't seek out a four-bolt main block, the answer is two-fold. First, this is the block we had and there are lots of enthusiasts out there who own them. So, we decided to stick with what we (and they) have. Second, our two-bolt block will be plenty strong enough for our envisioned horsepower levels and use of the car.
7 To properly find out what our main bearing clearances are, the first step is to use an outside micrometer (mic) to measure the diameter of the main journals on the crank.
8 The second step is setting an inside mic to the measurement we got from the crank journal.
9 Before installing our caps, the upper threads on the main studs were coated with ARP's lubricant, included with the main stud kit.
10 After installing the bearings and caps, all bolts were torque down to factory spec, 110 ft-lbs, in a three step increment of 40-80-110.
11 Using the inside mic based off the measurement of the main journal on the crank, Jason measured our bearing clearances starting from the back to the front of the block. There will be a natural amount of taper in the mains of a block, so our measurements of .004- , .004- , .00375- , .0035-, and .0035-inch were normal, but a tad on the loose side. The acceptable range of bearing clearance is from .003-.006-inch. You want the clearances as tight as possible without restricting oil flow, but when in doubt (for a street engine) it's always better to err on the looser side for safety and longevity. If your clearances come up out of spec either way, fear not. Bearing companies make different size bearings so you can adjust the clearance within tolerance.
12 With our bearing clearances checking out OK, we took the caps back off, dropped the crank in place, and torqued the caps back down again. The advantage of using premium fasteners for main and head bolts is you can use them multiple times before distortion from torquing will make them unuseable. In the case of cheap fasteners or “torque- to-yield” bolts, you can only use them once.