Evolution of Pent Roof Combustion Chambers

That become inside the past due fifties and I graduated to an old BSA 250cc motor cycle, a aspect valve gadget, and once again rode around the vintage farmer’s subject; for that reason started out my age-lengthy love of motorcycles.

Around then my Dad bought a Morris Minor; a 998 CC aspect valve engine with the L-shape combustion chamber, and I became capable of perform the preservation on it.

Soon OHV engines had been the fashion, then the OHC, all with various combustion chambers and finally the pent roof combustion chamber developed.

This is an article on Mechanical Engineering/Machine Design and specifically the blessings of pent roof combustion chambers. We start then with an overview of the IC engine, and then pass onto the exceptional designs of combustion chambers with the benefits of pent roof combustion chambers.

Overview of the Internal Combustion Engine
The version T Ford changed into one of the first mass produced vehicles to be powered via an internal combustion side valve engine constructed through the Ford Motor Company beginning in1908.( A widely known slogan – any colour so long as it is black?)

From 1932 they used a modernized model of this engine of their model Y vehicles. As an aside, the electrics had been powered by a dynamo and the windscreen wipers operated by a vacuum from the carburetor manifold. I do not forget these properly on Dad’s 1950 Morris Minor; the wipers used to slow down because the engine labored up hills!

On the motorcycle the front Harley Davidson used a aspect valve engine as early as 1919. The Davidson partner originally got here from pretty near my village, and every yr we’ve a Harley Davidson Rally with Bikers from all over the international attending – a awesome day out within the Highlands of Scotland!

Anyway, to continue, overhead valves and overhead cams (OHV and OHC) have been round for some time as well, however not exploited commercially until 1927 when Standard Motor Company introduced their V6 OHV engines, accompanied in 1949 by way of Oldsmobile. They produced an OHV engine operated via pushrods and suited to their Rocket V8, however earlier than that Norton Motor Cycle Company had produced a single OHC engine among 1925/26, that won the 500cc Isle of Man TT race in 1926.

OHV from wikipedia Commons by way of IJB TA

Oldsmobile Rocket V8 OHV engine from Wikimedia Commons via Zandome

The pent roof combustion chamber become apparently used first in the engine of the 1904 Welch Model 4.0 constructed by means of The Welch Motor Co., Pontiac, Mi.

1904 Welch Touring Car with Pent-roof combustion Chamber from earlyamericanautomobiles

Pent roof combustion chambers were additionally utilized by Chrysler among 1951 and 1958 whilst it turned into discontinued because of high fees. Honda Motorcycles were the usage of the pent roof combustion chambers around 1962, and I well take into account Mike Hailwood, their star rider and international champ pushing a 500cc Honda out onto the begin grid on the Ulster Grand Prix. We had been all searching out for a “Honda Six” on the time and this system had six exhaust megaphones poking out from the engine. Mike form of smiled at the cluster of photographers and dolly-birds round him, reached down, and removed two dummy exhausts – yep it was nonetheless the 4 cylinder version!

A 1966 model of the Honda 500cc ridden by means of Mike is shown under;

Mike Hailwood’s 500cc Honda of 1966 from Wikimedia Commons via Michael

Anyway, this became probably the first of the pent roof multi-valve engines produced by Honda and it blew all the competition away in TT racing: the emerging Yamaha and Suzuki two-strokes, even our antique Irish modern record holder, a 7R AJS rode via nearby hero Dick Crieth.

Technical Advances in Combustion Chamber Design
There were numerous combustion chamber designs of numerous shapes produced to attain the most reliable combustion efficiency of the gasoline. The combustion chamber includes top and decrease components; the top being the recess into the cylinder head, the lower along with the piston crown and top cylinder.

Four of the greater famous combustion chambers are examined under with easy sketches, please click on at the pictures to amplify:

Hemispherical Combustion Chamber

Symmetrical layout, valves similarly spaced with flat piston crown. This turned into the closest to the current pent roof layout, incorporating a hemispherical form cast into the cylinder head and became considered a compromise between manufacturing cost and engine efficiency. These typically have a central spark plug between the similarly spaced valves.

Wedge Combustion Chamber

Asymmetrical layout with valves spaced off-centre. Piston crown flat. This is one of the oldest designs and became used at one time or any other by almost all of the most important manufacturers of IC engines. The spark plug is placed at the thick end of the wedge, with the valves every side on the equal perspective because the wedge top edge.

**Bowl in Piston or Cup/Bowl

Bowl in Piston Combustion Chamber


This is a symmetrical combustion chamber layout with the valves similarly spaced and vertical; the piston being recessed to offer the combustion chamber shape towards the flat cylinder head. Favored extra through diesel engine manufacturers it produced a very turbulent go with the flow of combustion blend and become noisy.

Pent Roof or Crescent
Pent Roof Combustion Chamber

This is a combustion chamber of symmetrical design; multi- valves equi-spaced over crescent shape and at an attitude, the piston crown having a matching raised shape.

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