The Benefits of Simple Technology
"Far too complicated," said the critics of Buick's OHV inline eight-cylinder engine. The entire valve train—the pushrods and rocker arms mounted on top of the engine—was, they argued, an unnecessary complication. Some experts may even have been right about that, because the disadvantages of an inline-eight were real: the long, heavy engine block, which had to be quite thick-walled to be reasonably rigid, and the risk of a whipping crankshaft—even to the point of breaking. Moreover, it was of little use that while the valves in the combustion chamber facilitated gas flow, the single carburetor sometimes struggled to supply the farthest cylinders with a proper mixture. Siamese intake ports—that is, a bore with a “Y”-shaped branch for two cylinders—did little to help either; they often immediately negated the advantages of the improved OHV combustion chamber.
So there was a certain truth to it when Buick's competitors pointed out in movie commercials that the OHV configuration mainly meant more work and trouble. With an SV engine, the cylinder head could simply be unscrewed for the most important maintenance work.
It even says so right there: Valve in Head! In the 1930s, the OHV Buick engine—shown here is a 1946 unit—was also criticized for its “unnecessary” complexity. An SV engine was easier to work on.
Neither the inline-eight nor the SV engine survived beyond the 1950s. With the V8, Ford had already proven in the early 1930s that the V-configuration of the eight cylinders allowed for a more compact design and a lighter block. At the latest with the emergence of more modern OHV valve train systems after World War II, gas flow could also be sustainably optimized. The best example is Chrysler's Hemi engine with its hemispherical combustion chambers.
In Europe, many of these factors played a different role. The variety of design principles was significantly greater, and the choice of materials was also more diverse. And overhead valves were standard. In the 1960s, the overhead camshaft became standard even for everyday cars.
A compact, relatively rigid block in the Ford Kent “Crossflow” engine. Shown here in the Caterham Super Seven with the cylinder head removed—a task that is extremely easy to accomplish.
Why the Kent Was Different
When the Ford “Kent” engine made its debut in 1959 as the 105E in the new Anglia, it was traditional in some respects but highly modern in its details. Its design was traditional, featuring tappets and rocker arms, with a cast-iron engine block and cylinder head. However, it was the successor to an older side-valve engine. What was modern, on the other hand, was the thin-walled, material-saving casting and the comparatively short, rigid engine block.
Equally modern was its design as a short-stroke engine—and this in Great Britain, where vehicle tax had previously been calculated primarily based on cylinder bore. This led to engines with long strokes and small bores, which hinders gas flow: with a small bore, the valve diameter is soon limited by an insurmountable constraint. Even with valves arranged in a roof-shaped configuration—that is, at angles of up to 90 degrees to one another—there comes a point where further increases are no longer possible.
The Kent, however, was different, and it was powerful—even as a simply constructed OHV engine that was therefore very low-maintenance and easy to repair. As a short-stroke engine, it offered the ideal conditions for tuning: a comparatively large bore, providing ample space for decent valves, and no small valves—even when they're arranged parallel to one another. In addition, the cylinder head is rigid and thermally quite reliable, thanks to good water flow around the valve guides. Keith Duckworth and Mike Costin capitalized on this potential and struck out on their own by tuning the Kent engine: in 1958, they founded Cosworth and built their first engine based on the 105E/107E the following year.
My 1989 Caterham Super Seven “1700 Super Sprint”—it's supposed to produce 135 PS.
An Engine Built on a Kitchen Table
By the 1980s, the “Kent” was already a discontinued model at Ford—it had been replaced by the SOHC engine known as the CVH, short for “Compound Valve-Angle Hemispherical,” as found, for example, in the front-wheel-drive Escort Mk III. It was precisely during this time that Jez Coates, Technical Director at the small kit car manufacturer Caterham, to tune up the time-honored Ford Kent “Crossflow”—as a replacement for the discontinued Lotus Twin-Cam engines, which had essentially come as part of the deal when the rights to the Lotus Seven were acquired.
The cross-flow Kent had debuted in 1967 in the Ford Cortina Mk II and was available in the Seven from then on as 1300 and 1600 models. Coates, however, built a 1700 “Kent” at home on his kitchen table: He boosted the power from 86 PS with a 32 Weber downdraft carburetor to 135 PS using two Weber 40 DCOE carburetors, larger valves, and a sharper camshaft. As the Caterham Super Sprint, this engine finally went “into production” in the mid-1980s—if one could say that at Caterham.
One clear finding: the fourth cylinder blew its head gasket.
Boom—and that was it
The cylinder head gasket on exactly this kind of engine blew out on me during a track day in May. The failure came with warning signs: While warming up the engine, I hadn't noticed that the fan's thermostat switch wasn't working, and at some point I found myself dealing with boiling coolant. My hope that the engine—which is otherwise very robust thermally—would have survived this unscathed evaporated into steam after a few fast laps. Poof—and that was that.
Now, during the vacation season, I was finally able to take care of the car, remove the cylinder head, and take a look. As described above, thanks to the simple design, it was a matter of about 45 minutes. The only issue found was the aforementioned gasket; the block and head are flat, and thanks to my immediate intervention on the track, no further damage was sustained. The new gasket is back in place, and the head has been tightened according to specifications—with a warm-up, overnight cooling, and a controlled retightening afterward.
Now I need to replace the wire jumper that's currently keeping the fan running continuously—certainly not a major drawback in this weather—and install a new thermostat. Then I hope to be able to take the Seven out for a few more nice drives this fall. But as early as Saturday, I plan to drive it to the Safenwil Classic Car GP as a spectator. I hope it holds up! How do the British say it? “Fingers crossed!”
It's running again. After a short drive to bring it up to operating temperature and letting it cool down overnight, I retightened the cylinder head bolts.
