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Iron's Days Are Numbered as Auto Makers Cast Their Lot With Aluminum


Sheng Ingram is a believer in aluminum-block engines, thanks to his 1987 Acura Integra, which has clocked more than 200,000 miles without a major repair.

"Believe me, motorists can put their trust in an aluminum engine--at least Honda's," Ingram says, referring to the Japanese maker of the Acura luxury line. "Mine is running great and needs less than a half-quart of oil between oil changes every 4,000 miles."

But not everybody with aluminum engines is so enamored. The history of aluminum-block engines is full of disappointment and premature failure owing to warped cylinder heads, leaking seals, blown gaskets and worn cylinders.

As the auto industry abandons traditional cast iron in engine blocks and cylinder heads, consumers are clearly mixed in their acceptance of aluminum. Cast iron has a history and a reputation that are hard to dispute. When prehistoric humans needed tools, they learned to make use of iron, and the metal has symbolized durability and strength ever since.

Engine blocks, of course, are the heart of a quality engine, allowing efficient cooling and tight tolerances for crankshaft bearings, piston rings and camshafts. Auto makers have been casting with iron for a century and have significantly refined their processes in recent decades.

But there is a major shift to aluminum, and so many new aluminum engine designs are coming on the market that the capacity for casting aluminum blocks is one of the limitations holding back the phaseout of iron.

What's driving the trend is the continuing effort to cut vehicle weight and improve fuel economy. General Motors Corp.'s newest four-cylinder engine, for example, has an aluminum block that weighs 49 pounds, compared with 77 pounds for an equivalent four-cylinder with a cast-iron block. But aluminum is more expensive, costing about $2.50 per pound to cast, versus 40.5 cents per pound for iron, GM says.

The weight savings from the block typically can be doubled by reducing structural weight elsewhere in a vehicle, says Otto Willenbockel, GM's executive director of engine engineering.

GM, the world's largest auto maker, still builds most of its engine blocks out of cast iron, but it has introduced about half a dozen aluminum engines in the last few years and the majority of its new engine designs are aluminum.

Willenbockel, a German-trained engineer, says contemporary aluminum engines have reached parity with iron in their ability to provide long service and withstand consumer abuse.

"From a durability standpoint, there is no difference when you design it to the same targets," Willenbockel says. "You can design the strength you need."

Yet he acknowledges that many consumers remain unpersuaded, particularly truck buyers. All GM trucks are powered by cast-iron engines, though the company is preparing for its first aluminum truck engine. GM will introduce its Vortec 4200, a 4.2-liter inline-6 aluminum engine with 270 horsepower, for its 2002 Chevrolet TrailBlazer and Oldsmobile Bravada sport-utility vehicles.

All GM engines use cast-iron cylinder liners, either pressed or cast into the block. That ensures that even with aluminum blocks, the pistons and rings get the benefit of iron's hardness.

James Conley, a Northwestern University professor and an expert in engine casting, concurs that auto industry advances--first in Japan and Europe, and more recently in the U.S.--have made aluminum the equal of iron in terms of durability.


Despite advances in aluminum engines, they still cannot withstand overheating, contaminated oil or dirty coolant the way cast-iron blocks can, says Bill Whitney, president of Prestige Engine Co., a Dallas specialist in remanufacturing aluminum-block engines.

"They are definitely subject to premature failure," he says. "Aluminum-block engines are subject to blown intake and exhaust gaskets. They are the weak links in the chain."

The most serious problems with engines that use aluminum have come from two sources: designs that match aluminum heads and cast-iron blocks, and those that do not use cast-iron cylinder liners.

Aluminum heads mated to cast-iron blocks require carefully designed head gaskets. Ford Motor Co.'s 3.8-liter V-6 engines, for example, have a history of blown head gaskets and have been the subject of a contentious recall.

Owners of some BMW 530i, 540i, 740i and 840i cars built in the mid-1990s say they have experienced serious problems with M60 engines that use nickel coating on the aluminum cylinder walls. BMW has extended the warranty on vehicles equipped with M60 engines to six years or 100,000 miles.

Problems like those, however, are not going to reverse the industry trend toward aluminum. Aircraft, spacecraft and military vehicles have proved the validity of high-strength aluminum, according to the aluminum industry.

"You are going to see nothing but aluminum engines in the future," said Richard Klimisch, an Aluminum Assn. executive. "Safety, handling, acceleration, braking all gets better. That's what we're trying to sell."

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