Engines: Going back to the bark of the ‘two six bits’

by Tom Berg

RENO, Nev. – “You can’t go back,” the saying goes, because things just aren’t the same anymore … Maybe … But the 1,900 people who went to the American Truck Historical Society’s (ATHS) convention here last June, found that old things are better.

“Nostalgia isn’t what it used to be,” goes another saying. Most of the gloriously restored 525-plus trucks on display outside the hotel never looked so good. Shiny paint and polished, bright metal trim that masked the tough lives they led at the hands of now aged or deceased drivers, after workers now deceased, put them together on assembly lines long since closed. We can grow sad thinking about times past and people no longer with us. But for some reason, the sight of restored old cars and trucks bring smiles to our faces. So it was in Reno at the ATHS meeting.

Sound is also a powerful thing, and what’s more musical to our ears than the throaty note of a powerful diesel? Many old-time truckers will tell you that the most musical of all was the bark of a Cummins NHS-275, the legendary “Two Six Bits” of the 1950s.

Never heard it? Neither had I until I went to Reno. Several trucks at the show had NHS diesels, and their owners occasionally cranked them up for audio fun, and people quickly gathered to listen.

One owner was Dan Thomas of Medford, Ore., who displayed his ’55 Mack W-71 cabover and ’53 Mack LTL conventional. Both were meticulously restored in glossy dark green paint. And both NHS-powered. The long-nose LTL was a Mack Western machine, built in Hayward, Calif. LTLs usually had big Cummins diesels for West Coast-size grades.

The NHS-275 was near the summit of the 743-cubic-inch NH series, successor to the early H’s. The NH later evolved into the 855-ci NTC and is now the N14 (which is reaching the end of the emissions-legal road and due to be phased out soon). “S” means supercharged, and the NH’s ‘charger is grafted to the right side of the engine block. It’s gear-driven, and you can hear the gears whine as power builds.

The barking exhaust, though, is what really grabs your ears. It’s so compelling that Ken Talley of Madeira, Calif., has a trailer-mounted NHS tied to a pair of hefty disc brakes – a simple dyno that sets the big ol’ Cummins to work so folks can hear how it sounded while climbing an old mountain grade.

Talley fired up his Two Six Bits a couple of times each day of the convention. The after-sunset demos were light shows: After warming it, he revved it and loaded it with the brakes ’til they glowed red and a faint foot-high flame appeared at the tip of the chromed stack. It wasn’t really loud, just sharp – a bap-bap-bapping unlike anything I’d heard.

“That’s the way it was – nothin’ sounded like the NHS, and you could see the flame out the stack as one climbed a hill,” smiled one retired trucker. He was among scores of people who stood entranced at this show. That rapping comes from valves operated by the NHS’s unique camshaft, explains Dan Thomas’ friend, Jim Smith of Central Point, Ore. He went to a chromed display cam and pointed out that its lobes have an almost flat profile, causing the valves to pop open, stay wide open, then pop shut. As you know, cam lobes on most other engines are triangular, so valves open and close more gradually. Today’s turbochargers, not to mention quiet mufflers, further mute the exhaust note on modern diesels. Oh, they rumble and roar through the straight stacks that some guys run, but it’s not the same. Too bad.

Cummins diesels are still available in today’s Macks, but almost 99 out of 100 customers buy Mack’s own stout engines. And Mack lost most of the western business it had when it closed the Hayward plant more than 20 years ago. So for better or worse, things have changed. Aside from both Eastern and Western Macks, the Reno display included nameplates past and current: Diamond T, Autocar, Fageol, Sterling, Freightliner, Ford, GMC, Chevrolet and Dodge. Most numerous by far were trucks from the oldest American West Coast builders, Kenworth and Peterbilt.

Of course, there were also Western Stars and one or two Hayes Clippers. In fact, the American Truck Historical Society maybe ought to be renamed “North American” or “Can-Am,” because it includes five chapters and hundreds of Canadian members. Lots of them will be down for the organization’s next convention, in Kansas City, Mo. (home of ATHS’s new headquarters), from May 30 through June 1. For info, call ATHS at 816-891-9900, or go to its Web site, www.aths.org and use the current password, Kenworth.

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  • All other Cummins 743 cu.in. Diesels exited the exhaust out the center exhaust manifold the NHS exited out the rear and no. 6 cyl fired right into the pipe which is big part of its unusual exhaust sound my Dad owned a ‘48 Peterbilt with an NHS that he had set valve and injector timing way up and guessed it had 450 hp and he hauled logs with it in Northern California