402 Big-Block Rebuild, Part 4 - 1967 Chevrolet Chevelle SS

We put the top end together on our 402, and discuss how to break-in a flat tappet camshaft.

Patrick Hill Jan 24, 2014 0 Comment(s)
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1967 Chevrolet Chevelle 2/23

12. When installing head bolts, make sure the washers are oriented in the correct position. The chamfered edge should be towards the bolt head. They go this way so a stress point isn't created under the bolt head when it's torqued down. The head bolts are tightened down in three steps to 70 ft-lbs, 23-46-70. The order to torque the bolts in is available online, or in any service manual for a car that had a big-block. All Mark IV big-blocks use the same sequence.

1967 Chevrolet Chevelle Torque 3/23

13. With the heads torqued down, the Lunati one-piece pushrods (part no. 8200-16) are dropped in place. These will give us excellent valvetrain stability, thanks to their stiffness. If a pushrod has flex, not only can it create a power-robbing harmonic in the valvetrain that can lead to a failure, it also won't open the valve all the way. On a big-block, the intake pushrods are shorter than the exhaust pushrods. If you get them mixed up, you won't be able to set the valve lash properly.

1967 Chevrolet Chevelle Lunati 4/23

14. After putting a dab of AMSOIL assembly lube on the tip of the pushrod and the valve stem, the Lunati aluminum roller rockers (part no. 85350) are set on their studs. The rockers feature an extruded body made from aircraft quality aluminum, with a full roller trunnion, and the bodies are machined for valvespring clearance. We stuck with the stock big-block ratio of 1.7, but they are available in a 1.8 ratio.

1967 Chevrolet Chevelle Polylock 5/23

15. The polylock adjusters are hand tightened to the point where the pushrod can still be rotated with just two fingers with a little resistance. Since this is a solid lifter cam, we don't need to worry about lifter pump up to accurately set lash. Our cam calls for a cold lash setting of .020 thousandths on the intake valve, and .022 thousandths on the exhaust. On startup it will be a little noisy, but once the valvetrain heats up and metal expands, the lash will tighten up significantly, and the valvetrain will quiet down. This is normal with a mechanical cam, and the lash settings are set according to the cam profile, taking into account metal expansion.

1967 Chevrolet Chevelle Feeler 6/23

16. To set lash, Jason uses a feeler gauge. For the intake valves, the engine is turned over by hand until the exhaust valve has just closed. To set the exhaust valves, the engine is turned over until the intake valve just starts to open. This ensures (on both valves) that the lifter is on the base circle of the cam lobe, so the lash setting is accurate. Once lash is set, the polylocks are tightened on the rocker arm adjusters.

1967 Chevrolet Chevelle Harmonic 7/23

17. With cold lash set, we moved on to other parts of the engine. First, the timing cover was bolted in place, followed by installation of the harmonic balancer.

1967 Chevrolet Chevelle Vavle 8/23

18. After rotating the engine by hand one more time to make sure there was no interference in the valvetrain, the valve covers were bolted down, then our freshly cleaned and painted intake. We're going to start out with the factory cast iron intake for our first tests, but later on will upgrade to an aluminum one.

1967 Chevrolet Chevelle Number One 9/23

19. With the intake secured, the number one cylinder was rotated to top dead center (TDC) and the distributor installed, with the rotor pointing towards the number one cylinder. This will get the timing as close as possible until we get it fired up and set it exactly with a timing light.

Holley 750 Cfm Double 10/23

20. Our factory intake is flanged for a Holley carb, and for break-in we're using this Holley 750 cfm double pumper. We'll dial in our carb selection on the dyno in our next installment. For now, we know this carb works well, and will be just fine for the break-in procedure. A word from Jason, "You can turn the idle stop screw on the carb up a few turns just to make sure it will not just fire up, but get up to the right rpm quickly. You don't want to spend too much time cranking the engine before it fires, otherwise you'll wipe the break-in lube off the camshaft."

Comp Cams Break In Oil 11/23

21. For break-in we're using Comp Cams specially formulated break-in oil. Its proprietary additive package includes optimum amounts of ZDDP (Zinc and Phosphorous), Molybdenum and detergents, so the metal surfaces of the camshaft and lifters are fully protected while they burnish and mesh together during break-in. Once the engine is fully broken-in, we'll switch to AMSOIL's full synthetic Z-ROD high zinc oil to make sure we get long life out of our flat tappet cam.

402 Engine Start 12/23

22. At this stage, start up is very critical. You don’t want to have the engine cranking for a long amount of time, as it will greatly increase the odds of ruining the cam. Jason uses starting fluid, primes the carb, and gets his engines to fire up as quickly as possible. “Once it is running, you need to bring it right to 2,000 rpm, and run it for 20 minutes minimum. You don’t need ot keep it at exactly 2,000 rpm the whole 20 minutes. Varying the rpm keeps oil going to different areas of the engine, splashing it off the crankshaft at varying engine speeds.” says Jason. The first 10 minutes of run time are critical for cam break-in. With break-in complete, the oil is drained and inspected for any signs of metal in the oil. Then the oil filter is removed, cut apart, with the filter material inspected for metal shavings. Both were clean, meaning our big-block was good to go! Next up, we’ll hit the engine dyno to get the engine dialed in, and play around with some different things to see how they affect power.


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