Cammer: The Pontiac OHC Six

LEGACY

The next GM car to offer a belt-driven overhead camshaft was the Chevrolet Vega, which debuted in 1971. It spawned a Pontiac version, the Astre, in 1975, although Pontiac didn’t use the Vega’s 140 cu. in. (2,286 cc) OHC engine for long. In 1978, the Vega four was replaced by the 151 cu. in. (2,471 cc) pushrod “Iron Duke” engine, which Pontiac used well into the eighties.

By the late seventies, belt-driven overhead cams were becoming very popular, particularly on inexpensive four-cylinder engines. Sadly, many later timing belts were far less robust than Pontiac’s was and some OHC engines had an alarming tendency to eat valves if the belt snapped. By the beginning of the 21st century, concerns over belt longevity — and the high cost of changing a timing belt on a modern transverse engine — prompted a move back to timing chains. Timing belts are now becoming rare; even Honda has adopted chain drive for its more recent engines.

Hydraulic valve adjusters were slower to spread to other mass-market cars, although they began appearing on some luxury cars in the early seventies. They are now extremely common on OHC engines, in part because maintaining a constant valve lash helps to control exhaust emissions. (Having owned several cars that required valve adjustments every 15,000 miles (24,000 km), however, the author considers hydraulic lash adjusters a tremendous convenience.)

It’s unfortunate that the Pontiac OHC six became something of a dead end. The Sprint, in particular, offered a combination of decent power, modest weight, and respectable fuel economy that was not seen again on an American car for years afterward. Along with the turbocharged Oldsmobile Jetfire V8 of a few years earlier, it was one of the most sophisticated American engines of its era. It had its faults, but none of them was crippling and most can be rectified today with a competent rebuild and regular oil changes.

The stillborn OHC V8s are even more tantalizing. Even if they had made to production, it would probably have been on a very limited basis, like the earlier Super Duty engines, but if DeLorean and McKellar had had their way, they might well have spawned mass-production derivatives, if only for homologation purposes. It’s easy to understand why the prospect of bolt-on OHC heads for the GTO had Hot Rod‘s Eric Dahlquist salivating.

Alas, it was not to be. Only one of the engines made it to the street, a SOHC 421 that Mac McKellar received as a parting gift on his retirement in 1982. Installed in McKellar’s 1963 Grand Prix, it was a fearsome sleeper, a sad — and potent — reminder of what might have been.

# # #


AUTHOR’S NOTE

A little over a year after this article was written, we learned of the death of Malcolm McKellar, who passed away on April 8, 2011. He was 90 years old. McKellar outlived his former boss, John DeLorean, by six years: DeLorean died in 2005 at the age of 80.


NOTES ON SOURCES

Our sources on the development of the “Cammer” included Jim Black, “Buyer’s Guide: 1966-’67 Pontiac Le Mans Sprint,” Hemmings Muscle Machines June 2009, and “Pontiac’s Fantastic Six,” (n.d., The Pontiac-Oakland Club Overhead Cammers Chapter website, www.overheadcammerschapter. 150m. com/ history.html, accessed 10 April 2010); Marc Cranswick, Pontiac Firebird – The Auto-Biography (Car & Motorcycle Marque/Model) (Poundbury, Dorchester: Veloce Publishing, 2003); John DeLorean and J. Patrick Wright, On a Clear Day You Can See General Motors: John Z. DeLorean’s Look Inside the Automotive Giant (Chicago, IL: Avon Books, 1979); John Ethridge, “Tempest’s New Cammer!” Motor Trend Vol. 17, No. 9 (September 1965), pp. 40-44; Kit Foster, “1967 Pontiac Firebird Sprint: OHC from John Z’s PMD,” Special Interest Autos #150 (November-December 1995), reprinted in The Hemmings Motor News Book of Pontiacs: driveReports from Hemmings Special Interest Autos, ed. Terry Ehrich (Bennington, VT: Hemmings Motor News, 2001), pp. 118-127; Wick Humble, “1961 Pontiac Tempest: But cars aren’t supposed to have curved driveshafts,” Special Interest Autos #48 (November-December 1978), reprinted in The Hemmings Motor News Book of Pontiacs , pp. 78-86; Jeff Koch, “John Z. DeLorean: Thoughts and memories from the immortal creator of the GTO, 30 years later,” High Performance Pontiac February 1994, pp. 22-23; George Mattar, “1966 Progressive Pontiac: PMD’s advanced overhead-cam-six Tempest for 1966,” Hemmings Classic Car April 2005; Mike Mueller, “When Less Was More: Pontiac Overhead-Cam Six-Cylinder,” American Horsepower: 100 Years of Great Car Engines (St. Paul, MN: MBI Publishing Company, 2006), pp. 117-121; Eric Nielssen, “Pontiac’s New SOHC Six,” Car and Driver September 1965, reprinted in Car and Driver on Pontiac 1961-75 (Brooklands Road Tests), ed. R.M. Clarke (Cobham, Surrey: Brooklands Books Ltd., 1986), pp. 36-38, 59; Jan P. Norbye, “Sensational New OHC Six from Pontiac,” Popular Science Vol. 187, No. 2 (August 1965), pp. 37-41; and Jan P. Norbye and Jim Dunne, Pontiac 1946-1978: The Classic Postwar Years (Osceola, WI: Motorbooks International Publishers & Wholesalers, 1979).

Additional technical details came from Doc Frohmader, “Pontiac OHC” (2006, Webrodder.com, www.webrodder. com/ index.php? search=OHC& page=showStories&CID=, accessed 14 April 2010) and Donald J. Hoffman, 1966, “Hydraulic Lash Adjuster,” U.S. Patent No. 3,273,548, filed 29 September 1965 and issued 20 September 1966.

Information on Pontiac’s other OHC engines came from Eric Dahlquist, “Big Medicine from Pontiac,” Hot Rod March 1968, pp. 30-35; Don Keefe, “Dept. X: Malcolm ‘Mac’ McKellar’s 1963 Grand Prix is powered by the world’s only surviving OHC 421 Pontiac V8!” High Performance Pontiac October 1990, pp. 30-31; Rocky Rotella, “Pontiac V8 Engines – Photographing Legends,” High Performance Pontiac March 2010, www.highperformancepontiac. com/ tech/ hppp_1003_pontiac_v8_engines/ photo_08.html, accessed 10 April 2010; and Bob Wicker, “An Interview with Herb Adams” (January 2010, Pontiacs Online, www.pontiacsonline. com/ Herb%20Adams.htm, accessed 10 April 2010).

Additional background information on other American OHC engines came from “Evolution of the Wills St. Claire” (2008, Wills Ste. Claire Museum, www.willsautomuseum. org/ , accessed 11 April 2010); Roger Huntington, “Will Camshafts be Kicked Upstairs? Progress Report on Overhead Cam Development, Yesterday, Today or Tomorrow?” Motor Trend Vol. 16, No. 7 (July 1964), pp. 56-57, 90-92; and Pat Foster, “The Other Overhead-Cam Six,” Special Interest Autos #150 (November-December 1995), reprinted in The Hemmings Motor News Book of Pontiacs, p. 123.

Some information on the Red Baron came from Moldy Marvin, “The Tom Daniel Story” (2004, Ratfink.org, www.ratfink. org/ tomdaniel/, accessed 11 April 2010).

We also consulted the following period road tests: Jim Dunne, “’66 Tempest: A tiger in performance, a dog on gas,” Popular Mechanics Vol. 125, No. 5 (May 1966), pp. 82-84, 230; John Ethridge, “OHC in a Tempest,” Motor Trend Vol. 18, No. 1 (January 1966), pp. 46-49; John Ethridge, “Sporty Specialties: Cougar & Firebird,” Motor Trend Vol. 19, No. 5 (May 1967), pp. 34-37, 41-42; Jan P. Norbye, “How Hot Can a Six Get?” Popular Science Vol. 188, No. 6 (June 1966), pp. 70-73; “Pontiac Tempest Sprint,” Car and Driver December 1965, and “Pontiac Le Mans Sprint,” Car and Driver February 1967, reprinted in Car and Driver on Pontiac 1961-75 (Brooklands Road Tests); “Pontiac Tempest Sprint & GTO: It’s Still….Six for the Money and Eight to Go!” Car Life May 1966, reprinted in GTO Muscle Portfolio 1964-74 (Muscle Portfolio Series), ed. R.M. Clarke (Cobham, Surrey: Brooklands Books Ltd., 1998); “A Brace of Birds: The Sprint and the 400 from among Pontiac’s Five Firebirds,” Car Life August 1967, John Ethridge, “Fire Breathing Bird…first of the spring from Pontiac,” Motor Trend Vol 19, No. 3 (March 1967); “Firebird Sprint: The Sensible Supercar,” Cars December 1967; Steve Kelly, “How Do You Say ‘PFST’?” Motor Trend Vol. 19, No. 7 (July 1967); “Look What They’re Doing to the Firebird Now,” Car Life April 1968; Jon McKibben, “Fitch Firebirds: With the Corvair market diminishing, John Fitch finds another car to improve,” Road & Track April 1968; and “Pontiac Firebird Sprint,” Road & Track June 1967, all of which are reprinted in Firebird and Trans-Am Muscle Portfolio, 1967-1972, ed. R.M. Clarke(Cobham, Surrey: Brooklands Books, Ltd., 1998).

We later updated the article to note the passing of Malcolm McKellar, based on information from Paul Stenquist, “Malcolm McKellar, Pioneer of the Pontiac Overhead-Cam Engine,” New York Times 3 May 2011, wheels.blogs.nytimes. com/ 2011/ 05/03/ malcolm-mckellar-pioneer-of-the-pontiac-overhead-cam-engine/, accessed 15 June 2011). We confirmed McKellar and DeLorean’s dates of birth and death via the Social Security Death Index.


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14 Comments

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  1. Great article Aaron! Milt Schornack of Royal Bobcat fame had some good words concerning the OHC six in his book. It appears they did some testing with headers and a tri-power setup on the sprint six engine. It would be quite the sleeper if it weren’t so loud.

    1. Pontiac did some similar experiments — the PFST project, developed by Herb Adams, used three Webers and headers. It was a pretty good setup, but it was too noisy to pass muster, and GM had banned multiple-carburetor setups.

      (Once interesting side note is that McKellar’s engine guys tried to create a common baseplate for the Tri-Power set-up so they could tell the corporation it was a single six-barrel carb. It didn’t work, though.)

  2. Grandpa was a Pontiac man for years – I was carsick numerous times as a young boy in the back seat of his 1966 Tempest OHC-6/Powerglide four-door.

    Years later, the car ended up in my hands, but the top end of the six had already died – I pulled the engine and replaced it with a Chevy 350 and THM350. Always loved that car – the dash was jewel-like with its deep-set gauges, and I always marveled at the “Wondertouch” power steering and brakes.

    The car is long gone, but I still have the OHC valve cover up in the attic somewhere – always thought it was a true piece of automotive art.

    1. Top-end oiling was a persistent problem with these engines when they were new — inadequate flow to the cam covers, particularly when the oil was dirty. I’m told that with modern oil and regular changes, it’s not a big deal, but it killed a lot of cammers when they were new(ish).

  3. How does an engine designed by (presumably) capable, experienced engineers make it into production with a design flaw like this?

    1. Mac McKellar actually took pains at the design stage to reduce camshaft wear; the lobes were twice the normal width, for example, in an effort to reduce surface pressure. However, hand-assembled test engines may not reveal issues that crop up with assembly-line engines owned by people who only change their oil once a year.

      As I understand it, the camshaft damage to the ’66 and ’67 engines was usually caused by one of three things:

      1) Incorrect machining of the metering hole in the restrictor that that controls the flow of oil to the camshaft journals. A lot of ’66 and ’67 engines came through with too large a metering hole, effectively reducing oil pressure to the cam and lash adjusters. This problem could be exacerbated by an incorrectly machined or clogged primary oil passage (the line through which oil flows to the cam cover), which could happen with infrequent oil changes or poor-quality oil.

      2) Too rough a finish on the contact area of the cam follower, where the follower actually touches the cam lobe, scuffing the cam.

      3) Broken retaining clips. The ’66 and ’67 engines used little metal spring clips to hold the lash adjuster to the cam follower during assembly. This was just an assembly-line convenience; once the cam cover is assembled, it’s not necessary. However, they just left the clip in place on the assembled engines, which would occasionally break when the engine was running, damaging the cam and/or valves with the pieces. The later engines omitted the clips, and simply removing them from the 230 will avoid the problem.

      For the most part, these were manufacturing/assembly issues, rather than design problems. Without talking to old Pontiac engineers, I don’t know why they weren’t fully resolved until the ’68 model year; if they’d been taken care of in the first few months of production, I’d file them under “teething problems.” I assume it comes down to the fact that design engineers don’t control production, and vice versa, as happened with the con rod breakage on the Fiero engines years later. (In that case, Saginaw foundry division was aware of the metallurgical problems, but they had no incentive to fix them.)

  4. This engine should have been an option in the 73-74 Ventura GTO. With an appropriate suspension and steering it would have been an excellent road car for the time and sales would have exploded during the first oil embargo.

  5. Can anyone help with a diagram of the timing marks for a 68 Pont Firebird 6 ohc engine. It would be greatly apprecceiated. Thanks.

  6. I have a OHC 6 without a Z (code) build date I think is L076 (DEC. 7th 1966) But can not find any code starting with a Z? I was told this engine was never loaded into a car or frame and was sent to a school for testing? Do you thoink there would be any truth to this? Thank you Rick

  7. I thought the cammer poncho was awesome,–especially the Sprint, and I wonder–do blue prints/photos exist for the never-produced DOHC 389? Or even the SOHC 421 & SOHC 428? The tri-power OHC-sprint? Taking a page out of Govt., I wonder what “vices” those jerk-Globalist(imo) Board Members of GM had–evidently none that Delorean was able to exploit. I mention this because Pontiac is no more but for idiots that didn’t want to “ruffle” Govt. feathers, like the moribund Roach and the drooling Donnor-Dumber–two killers of Pontiac-Power, and Legend.

    1. I assume the blueprints for those engines still exist in the files somewhere (certainly for the SOHC — as the conclusion mentions, Mac McKellar ended up with one of the prototype engines). It’s possible some of the prototypes are in the Heritage Center, along with other abortive GM engines like the SOHC Cadillac V-12, but I haven’t checked.

      It’s easy to understand why the SOHC and DOHC V-8 projects ended up not going anywhere, regrettable as it may be. Pontiac already had engines more powerful than senior corporate management thought was prudent; the division didn’t have a NASCAR program where a hot SOHC 421/428 would be really useful; and price escalation and insurance rates were already making the really hot cars unaffordable to most of the kids who wanted them. And that’s without even getting into the emissions certification issues. If the SOHC/DOHC engines had made it out of experimental, they probably would have been roughly as attainable as the Ford SOHC 427 or Chevy’s early Z-11 427 “Mystery Engine.” For the street, a Ram Air 428 or 455 would have been a lot cheaper and probably more practical.

      Still, I would be lying if I said I didn’t find the idea of a Trans Am 303 with overhead cams intriguing…

  8. I need a starter for a 1967 firebird,4.1 liter overhead cam sprint with a two speed power glide trans. or a gm part number, picture anything thanks in advance Tony

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