1962 Plymouth Valiant - Slant Six - Project Build

Gene Ohly at Evans Speed Equipment prepared the rare alloy block forassembly. The integrally-cast iron liners had some scratches, so theywere bored 0.020 oversize. The liners are a mere 0.10 thick, so the lessmetal removed, the better. Iron blocks can safely be bored in excess of0.060. Ohly also align-honed the mains, burnished the lifter bores, andsquared the deck surface. The fully machined block weighs 64 pounds, 70pounds less than iron.

Addressing the different rate of thermal expansion between aluminum andsteel, Chrysler employed unique upper and lower main-bearing caps. Theupper caps (installed in the block) are specific to aluminumapplications and feature roll sleeves to assure proper positioning. Thesleeves are used on the driver side of the block only and must never beinstalled on the passenger side. A critical oil passage intersects thepassengerside main cap bolt hole to feed oil to the main bearings. Afteralign-boring, iron-block lower caps can be used with aluminum blocks.

Although the aluminum block has no cam bearings, any Slant Six cam fits.Thanks to the continuous oil bath present in the area during operation,lubrication is assured, even when high-pressure valve springs are used.

The main-bearing oil-feed holes differ in iron and aluminum blocks.Here, a pen points to the lower hole used in iron applications.Fortunately, virtually all Slant Six main-bearing sets sold today arealso drilled with the higher hole required by the aluminum block. Thegrooved upper shells and nongrooved lower shells of our Enginetechbearings are adequate for our 5500-rpm ceiling. Main-bearing clearanceis 0.002.

To help prevent leaks, Doug offsets the rear main seal in such a waythat the gap is not aligned with the cap and block parting line. Theneoprene seal has a lip that acts as a one-way, valve-to-oil passage.The lip must face inboard, toward the crankshaft, for proper function.

The crank is from a '72 donor engine with minor polishing. Though allSlant Six cranks produced between 1960 and 1976 are beefy forgings,those from 1968 and later feature a 2.160 diameter flywheel/flexplateregister that accepts commonly available torque converters andflywheels. The pre-'68 register is smaller (1.960 diameter) and must usehard-to-find corresponding transmission components. All forged cranksare neutrally balanced, so mixing production parts rarely causesproblems. Cranks manufactured in 1977 and later are made of cast-nodulariron and have narrow main and rod bearings. Cylinder blocks, cranks,rods, and bearings from 1977 and later engines will not interchange withearlier Slant Sixes.

The main bearing bolts are tightened to 50 lb-ft (versus 85 lb-ft foriron blocks) to suit the physical properties of the die-cast aluminumblock. Antiseize compound is applied to prevent thread and shouldergalling. Chrysler testing revealed that if the thread engagement of thecap bolt into the aluminum is 21/2 times as long as the thread diameter,the bolt shank fails before the host aluminum. The special 1/2x13 capbolts are an inch longer than those used on iron blocks and featurereduced shanks to provide aluminum-compatible stretch characteristicsand to allow the passage of oil through the bulkheads to the mainbearings. Crankshaft endplay is 0.045, the same as an iron block.

Basic, rugged, and cheap, stock 6.7-inch forged rods with ARP 3/8-inchfasteners and cast-aluminum Enginetech 0.020 oversize pistons can handleplenty of abuse. The slugs weigh 16.4 ounces, and ours came sized within0.00025 diameter and 2 grams of each other. The Sealed Power chrome-molyrings ensure fast break-in and have 0.014 endgaps. The rods weigh 26.8ounces and should be installed with the oil squirt holes facing thepassenger side. The D-shape heads of the ARP rod bolts require a minorspot-facing operation on the rod shoulder for proper installation.Rebalancing of these stock-replacement parts is a luxury we skippedwithout consequence. Rod-bearing clearance is 0.001.

In a previous issue, we told the story of the aluminum block Slant Six and how its brief production run (1961-'62) was cut short by manufacturing difficulties and unexpected costs. This month we team up with Slant Six engine guru Doug Dutra to show you how to build a Slant Six that'll make 1hp/cubic inch, live with 91 octane unleaded, and run low 14s at over 90 mph in a 3,000-pound A-Body while remaining totally streetable and delivering 15 mpg.

Our buildup is based on a cherry aluminum block that somehow managed to escape the terminal, from-the-inside-out corrosion that renders most surviving blocks useless. Though our alloy wonder weighs 70 pounds less than much more common cast-iron blocks, if you follow our recipe with your iron block, you'll get identical results.

Note for the following: (a) Included in price of '72 donor motor; (b) Optional

Recipe List