The Chopped Buick V8 So Rough Jeep Bolted A 50-Pound Flywheel To It
Buick didn’t set out to build one of America’s most unusual V6 engines. It wanted a cheaper way to give the compact Buick Special six-cylinder power without developing an entirely new engine, so engineers adapted the architecture of its existing 90-degree V8. The shortcut worked on the manufacturing line, but it left the V6 with a V8-derived crankshaft and an uneven firing pattern that made for more vibration than a conventional six should have. When Kaiser-Jeep adopted the engine as the Dauntless 225, it tamed that vibration in wonderfully old-school fashion, with a flywheel weighing roughly 50 pounds.
Buick Built a V6 by Reworking Its Existing V8 Architecture
The early 1960s were not exactly a quiet period for American engines. V8s were getting smaller, compact cars were becoming more important, and manufacturers were looking for ways to give smaller vehicles enough power without filling the engine bay with an enormous lump of iron.
Buick already had a useful starting point in its compact 215-cubic-inch V8, introduced with an aluminum block and heads. The trouble was that a conventional inline six-cylinder was too long to fit the Special’s stubby Y-body engine bay. Buick engineer Joe Turlay, who’d already designed that V8 and the legendary Nailhead before it, figured the division could get a six-cylinder engine into showrooms fast by slicing the two front cylinders off it, rather than spending months designing something new from scratch.
The first version, introduced for the 1962 Buick Special as the Fireball V6, displaced 198 cubic inches and produced 135 horsepower and 205 lb-ft of torque. That decision made the Special the first American passenger car to use a V6 in volume production. Sharing so much tooling with the V8 kept costs down and got the engine into production fast, but keeping the 90-degree bank angle meant the V6 inherited crankshaft geometry that was never designed for six evenly spaced cylinders.
The problem was hiding inside the crankshaft. A conventional V6 has six cylinders arranged so that, with the right crankshaft design, each cylinder can fire every 120 degrees of crankshaft rotation. Buick’s 90-degree V6 didn’t have that luxury. It retained a V8-style crankshaft arrangement with three crankpins, with two connecting rods sharing each crankpin. That arrangement made sense for the V8 architecture Buick was starting from. It was much less natural for a six-cylinder engine. The result was an engine that looked like a straightforward V6 from the outside but had a distinctly unusual rhythm inside.
The Crankshaft Created a 90-150-Degree Firing Pattern
This is where the Buick V6 gets properly weird. A six-cylinder four-stroke engine completes one firing cycle every 720 degrees of crankshaft rotation. If the firing events are evenly spaced, dividing those 720 degrees between six cylinders gives an interval of 120 degrees between each combustion event. An eight-cylinder engine solves that math by design, with enough evenly spaced crank throws to keep the pulses smooth. Buick’s V6 couldn’t lean on the same trick.
It kept the 90-degree cylinder banks of its V8 origins and a crankshaft with three crankpins positioned 120 degrees apart, each one shared by a pair of cylinders. Because of that geometry, the cylinders could not fire at equal intervals. Instead, the engine alternated between 90 and 150 degrees of crankshaft rotation between firing events. Ninety degrees, then 150, then 90 again, continuing around the crankshaft. That’s what earned the engine its odd-fire designation. The firing order was completely deliberate, just not evenly spaced.
The original firing order was 1-6-5-4-3-2, and the uneven crankshaft timing gave the engine its characteristic roughness. At low engine speeds, those irregular power pulses were particularly noticeable. Instead of receiving six evenly spaced pushes during every two revolutions, the crankshaft was being accelerated and decelerated in an uneven rhythm.
Buick could manage some of the resulting vibration with conventional engine-balancing techniques, including counterweights and mounting. The engine wasn’t some mechanical disaster waiting to destroy itself. It was simply a compromised layout that needed more engineering work to make its behavior acceptable. That distinction matters. The odd-fire V6 could still make useful power in a compact package; what it lacked was the smoothness people expected from a conventional six-cylinder engine. When Jeep got hold of it, smoothness was hardly the first thing on the priority list.
Jeep’s Dauntless 225 Was the Rough-Running V6 With a 50-Pound Flywheel
Kaiser-Jeep saw something Buick no longer wanted. It was a compact engine with considerably more power than the four-cylinder engines available for its small Jeeps, and it fit as easily in the CJ-6 and Jeepster Commando as it did the CJ-5. The heavier Jeepster Commando needed the power most, up against V8 options in rivals like the Ford Bronco and International Scout.
The Buick V6 had grown from 198 cubic inches to 225 cubic inches by 1964, and Kaiser-Jeep began offering it in the CJ-5 for the 1966 model year, badged as the Dauntless 225. Buick dropped the V6 after the 1967 model year and sold the manufacturing line to Kaiser-Jeep, which later passed into AMC’s hands. For a CJ, the V6 made a lot of sense, compact enough for the Jeep’s tight engine bay while rated at 160 hp and 235 lb-ft of torque. That gave the little Jeep considerably more muscle than its modest dimensions suggested.
But Jeep inherited the odd-fire crankshaft along with all the useful parts of the Buick engine. This is where the famous flywheel comes in. The Jeep version used an exceptionally heavy flywheel, commonly cited at roughly 50 pounds. The extra mass gave the rotating assembly more inertia, smoothing the uneven pulses from the odd-fire crank without changing the firing pattern itself.
There is something wonderfully blunt about that fix. Rather than redesign the crankshaft, Jeep just let a huge spinning mass smooth things out, and that mattered more in a CJ than it would have in a sedan. Low-speed crawling over rocks and ruts is exactly where uneven power pulses show up most, and the heavy flywheel became part of the Dauntless’s character as a result. The flywheel wasn’t fixing the crankshaft problem. It was managing the consequences. And the consequences didn’t stop at the back of the engine.
The Odd-Fire Crankshaft Even Made the Distributor Weird
The uneven firing pattern affected the ignition system as well. Because the cylinders fired at 90- and 150-degree intervals, the distributor had to match that rhythm. It spins at half crankshaft speed, so those 90- and 150-degree crankshaft intervals become 45- and 75-degree intervals inside the distributor cap. The ignition system therefore had to account for that uneven rhythm, with the distributor working around 45- and 75-degree intervals rather than the evenly spaced 60 degrees of an even-fire V6.
Get the distributor even slightly wrong on this engine, and it won’t just idle rough. It’ll fire out of sequence entirely, a detail that turned more than a few home mechanics into reluctant experts on odd-fire ignition systems. It’s a small detail, but it shows how deeply that original crankshaft decision reached. The flywheel had to smooth the uneven power pulses, the engine mounts had to isolate the vibration, and the ignition system had to deliver sparks on an uneven beat. All three of those fixes trace back to the same three crankpins Buick borrowed from its V8.
That’s why calling this simply a V8 with two cylinders removed misses the interesting part. Buick found a clever, inexpensive way to build a V6, but the resulting architecture meant engineers had to work around its own firing pattern for years. For Jeep, that compromise was fine. The Dauntless was compact, torquey, and useful, and CJ buyers were hardly expecting their off-road workhorse to idle like a luxury sedan. GM eventually wanted something different.
GM Finally Fixed the V6 With a Split-Pin Crankshaft
By the early 1970s, the very engine Buick had once decided it no longer needed suddenly looked attractive again. The 1973 oil crisis had changed the economics of the American car industry. Large V8s were becoming harder to justify, and a compact V6 offered a way to give midsize cars useful power without the fuel consumption of a big eight-cylinder engine.
GM reacquired the Buick V6 tooling from AMC in 1974 and brought the engine back into production, now bored out to 231 cubic inches. So much of the existing design and manufacturing infrastructure could be reused that Buick reportedly had it back in production just 137 days after getting the go-ahead. But the same basic odd-fire problem was still there, and the real fix didn’t arrive until 1977.
Rather than abandon the 90-degree architecture, Buick redesigned the crankshaft with split, offset crankpins so the cylinders could finally fire at evenly spaced 120-degree intervals. That turned the original uneven 90-150-degree pattern into the smooth firing sequence a conventional V6 should have had from the start.
That fix mattered for more than a smoother idle. The even-fire crankshaft became the foundation for turbocharged versions of the V6, including the engines that powered Buick’s Grand National and GNX muscle cars through the 1980s. The fix didn’t erase the engine’s odd-fire history. That original 90-degree V6 had already lived a full life as the Dauntless 225, and its compromises had become part of its identity. But the same basic architecture, eventually badged the 3800 Series, would stay in GM production for 47 years, into 2008. For an engine born from a cost-saving decision, it certainly created an impressive amount of engineering drama.
Sources: Bring A Trailer, Mecum, Classic.com, Jeep, Buick
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