Chevy 348 Big Block Engine Restoration - 348 Revival

Several shallow notches are all it takes to restore free movement. It's imperative to mock up any stroker assembly prior to final cleaning so hassles can be nipped in the bud.

Edelbrock warns that its Performer RPM 409 heads must be limited to 0.550 maximum valve lift when installed on 348 blocks to prevent valve-to-block contact. Here a light checking spring and dial indicator are used to verify Edelbrock's warning with the head mounted to our 348 block. Sure enough, when pushed farther than 0.550, the exhaust valves come into solid block contact. We're running an Isky 0.639 solid-roller cam, so action is needed.

Here's a view of the trouble spots from inside the crankcase. While 409 blocks feature larger 4.312 bores and are not lift-restricted with Edelbrock heads, the big 1.720 exhaust valves (1.65 is stock) don't clear the 348's smaller cylinders despite our 0.030-inch overbore.

While the 2.190 intake valves are good to go on the 348, the W's staggered valves rely on machined pockets in the block for safe exhaust valve clearance. We need to make the pockets deeper with an Isky valve-notching tool (right). Its 1.750-diameter cutting head is slightly larger than the exhaust valve.

With plenty of moly grease to protect the valve guides, the heads are mounted to the block and a drill motor spins the cutter against the valve pockets. It only takes a 0.125 plunge to provide safe clearance for up to 0.700 valve lift.

The pen points to the reworked valve pocket. All 348 blocks feature these machined pockets, as do '62-66 409 blocks used in truck applications. Their impact on the final compression ratio must be taken into account when ordering pistons since they contribute to total chamber volume.

High-pressure valve springs (over 350 pounds) tend to smear rebuilder-grade cam bearings. Use hardened '55-63 small-block cam bearings from Durabond to solve the problem (PN CHP-4). The first four are a direct fit, but the No. 5 bearing needs to have a trio of oil feed holes drilled as indicated by the pointers.

The oil feed holes in the No. 5 cam bearing work in conjunction with an oil channel on the rear cam journal. Failure to use the correct bearing or the mistaken use of a non-grooved cam will lead to oil starvation to the lifters and valvetrain.

The Eagle stroker crank rides on semigrooved Federal-Mogul main bearings (PN 4036M). The main cap nuts torque to 100 ft-lb, the outboard bolts to 65 ft-lb.

Compared to the stock forged rods (right) the 6.135-inch Eagle H-beams (PN CRS61353D) look like tree trunks. At 780.7 grams, the new rods are 82.9 grams heavier than the old rods.

The forged 11.7:1 Ross pistons (PN JC120905) weigh 782.2 grams, 173.2 grams less than the stock 955.4-gram cast 9:1 slugs (right). They more than make up for the extra heft of the upgraded rods. Low-drag Total Seal gapless rings (PN M0690-35) are worth 10 hp and use a Napier-style second ring for oil contro

The unique angle of the 348 deck requires a band-type ring compressor. It's thin enough to slip into the wedge-shaped combustion chamber before coming to rest atop the 0.030-wide shelf surrounding each cylinder. Without the counterbore, you'll never get the rings into the block.

With the piston at TDC, the sloped dome creates a 59.76cc wedge-shaped combustion chamber. Since the head surface is flat, you cannot build a positive deck W-motor, as the pistons would smack the heads.

The Eagle rod caps torque to 63 ft-lb and use Clevite 77 rod bearings (PN CB-743HN). Oil clearance is set at 0.0025 inch.

The W-motor accepts small-block oil pumps, so a Melling 302 Z/28 high-volume unit gets the nod (PN M-99HV-S). The pen in the photo points to slight interference between the pump body and the No. 5 main cap stud. Grinding a small notch in the pump body restores clearance.

Stock 348/409 crank snouts accept small-block dampers, but differences in keyway placement invalidate the TDC mark. The Eagle stroker crank corrects this W-specific quirk with a conventional keyway position so a PRW 6.75-inch damper slips right on (PN 30501). The rotating assembly is internally balanced.