DMU Engines

Leyland 680 150hp Engine

Introduction

BUT supplied two types of 150hp engines, the 'A' type (AEC 220) and the 'L' type, which was a Leyland 680.

This was a horizontal six-cylinder 11.1 litre diesel engine with direct-injection, overhead-valve, four-stroke unit with a pump-driven water circulation system. Valves, rocker gear and injectors are carried in the two detachable cylinder heads, each head covering three cylinders. The valves are push-rod operated from the tappets and camshaft through rocker levers.

The crankcase and cylinder block form a monobloc casting, the cylinder bores being fitted with renewable liners. The gear-driven crankshaft is also housed within the crankcase.

The crankshaft is carried in seven thin-shell indium coated copper-lead bearings and carries a vibration damper at the front end.

The pistons are fitted with three compression rings, the top ring being chronium plated, and two scraper rings. The combustion chamber in the piston crown is of torodial form. The fully-floating gudgeon pins are retained by circlips.

The timing gears consist of a train of helical gears which drive the camshaft, fuel injection pump, water pump, compressor and engine tachometer generator through two idler gears driven by the camshaft gear.

Lubricating oil is pressure fed by a gear-type pump to the bearings etc., through drilled oilways. A by-pass centrifugal oil filter is incorporated in the system.

The fuel injection pump is mounted on the inner sump face and incorporates an idling and maximum speed governor and a diaphragm type lift pump. Multi-hole fuel injectors are fitted.

On later engines all electrical leads are carried in conduit and connected to a Niphan plug-and-socket, enabling the engine to be removed and replaced without disconnecting the terminal connections from the various components.

An oil-bath type air cleaner is mounted on the car underframe and is connected by hose to the inlet manifold.

A water-cooled oil cooler is mounted on the engine.

Variants

The 680 was a popular Leyland engine also used extensively in road vehicles in both horizontal and vertical forms. As the engine developed over the years, some variants found their way onto DMUs. The differences are listed below. Later the turbocharged variation, the TL11, was also used. The table is from a BR document dated 9/89.