EarlyCJ5.com Technical Library

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Hubbard's V6 History

By John Hubbard

The Buick Two Hundred and Twenty Five Cubic Inch, odd-fire (1-6-5-4-3-2), V6 engine was purchased from GM by Kaiser Jeep Corporation in 1965 and used in CJ's (CJ5's and CJ6's) until 1971. Buick purchased the engine back from AMC in 1974. The Buick V6 after 1974 came in both an odd-fire 231 cubic inch engine (until mid 1977) and an even-fire 231 (after mid 1977). The Buick engine after 1979 is referred to as having "late model" heads and intake manifolds and other items manufactured for the earlier odd-fire models do not fit the later models after 1979.

An f-head, 4-cylinder jeep engine weighs about 404 pounds and puts out about 75 horsepower. The Buick 225 weight 414 pounds and puts out 160 horsepower (unmodified). One drawback of the odd-fire design is a rough idling engine that is hard on timing gears and tough to keep timed. The odd-fire engines have a stronger crankshaft than even-fire Buick engines due to the fact that the even-fire engines redesigned the crankshaft journals (split them) in order to run in an even-fire mode--this weakened the crank considerably.

The 225's advantage over the f-head 4-cylinder is clearly horsepower and torque and its compact size. Its advantage over early even-fire 231's is a stronger crank. Its advantage over later model 231 engines lies in the engine's simplicity and the reliability of the stock Rochester 2 barrel used to deliver fuel. At slow speeds--a Buick 225 V6 engines mated to a manual transmission (big flywheel) will idle vehicle over the trail with just 2 cylinders firing--the momentum of that large flywheel keeping the engine running. At highway speeds the Buick 225 will purr along and still get 15-20 mpg (depending on gearing).

The following is a story told to me (and scripted here to the best of my memory) by Marv Fox who used to work in the parts area of Hayes Brothers Buick/Jeep in Salt Lake City, Utah during the 1960's:

In the early 1960's the Hayes Brothers Buick/Jeep dealership was doing V6 engine conversions on Kaiser CJ5's. Hayes Brothers, being a Buick dealership, would purchase a new Buick V6 from Buick and receive it (crated) and install it into the Jeep for the customer using new Buick motor mounts. Towards the mid-60's Jeep became aware of the large number of V6 conversion that were being done by Hayes Brothers and they made arrangements to send a team of engineers to Salt Lake.

The Jeep engineers arrived in Utah and basically witnessed a CJ5/V6 conversion from start to finish. They saw the F-head motor being taken out, the new motor mounts being fitted and the new engine being mated to the Borg Warner T90 transmission. They thanked Hayes Brothers. Loaded the Jeep onto a railroad car and took it back with them to Ohio.

The engineers took the vehicle back to a test track in Ohio and ran it through grueling tests designed to test the durability of the engine conversion. They were very impressed by the Jeep's durability and obvious power/torque gains. Within a short time after the engineers left Salt Lake City it was announced the Kaiser Jeep Corp. had purchased the rights to manufacture the Buick 225 V6 engine and shortly after that CJ5's and Jeepsters were being offered to the public with a V6 option (1965 for the 1966 model year). This option included a fully-synchronized 3 speed or optional 4-speed. The Jeepsters also had the choice of a GM TurboHydromatic Automatic transmission mated to the Buick V6.

Editorial Note: I believe that this story happened exactly as described above. However, I also believe that Kaiser Jeep Corp. was aware of a pressing need for more power in the late 50's and early 60's CJ5 model and needed a new power plant for the CJ5 and future vehicles that were on the drawing board. It is not known by myself or Marv Fox if other engineering teams were sent to other parts of the USA to witness other conversions and bring back other specimens. It is also not known how long Kaiser Jeep Corp. was in negotiations to gain rights to the Buick V6 before they made their announcement regarding its acquisition.

The following is a list of modifications being performed on the 225 currently being rebuilt to go into my 1953 CJ3B project. The original engine was from a 1968 Jeepster with a 3-speed.

Replace stock intake manifold with Holley 4 bbl manifold model 300-22
Install Holley Pro-Jection 2-Barrel TBI Fuel Injection
Replace stock exhaust manifolds with rear-exiting manifolds from a Buick 231
Replace stock ignition with GM HEI
Replace timing chain set with Cloyes True Roller set

Link to Ken Mosher's Buick V6 History--Includes Even and Odd-Fire.