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The Teagle engine

by Kenneth Crago

Although now retired for quite a while, I was Designer at Teagle at the time when we used to make petrol engines, approximately 1952 to 1964.  Previously I was on the design staff of D Napier and Son, Acton, London on aero engine design, a bit too large for your interest.

The firm of Teagle was started by Mr W T Teagle, originally a farmer, and still very energetically concerned with the firm as managing director and also very concerned with the design of new implements.  The firm progressed from very humble surroundings to now three factories embodying some of the most modern machine tools and equipment.

We produced two basic engines: a two-stroke 50cc and a four-stroke 126cc; both being produced due to necessity, which is the usual reason.  The 50cc was designed as part of a manually carried and operated hedge cutter.  The unusual feature of having the belt pulley central was for a variety of reasons.  It provided the correct balance of the engine in the machine, it enabled an on/off clutch by tightening the belt and it enabled the use of an overhung crankshaft.  It also widely spread the crankshaft bearings, a desirable factor.  The overhung crankshaft enabled a case-hardened crankpin, the use of a needle roller big end and a lower standard of lubrication, a very necessary feature where farmers were concerned!  The crankshaft was made in three parts: the main shaft, web (a stamping home-produced) and a high nickel case-hardened pin.  The shaft was welded with the pin under water, thus retaining its hardness.  The crankcase & cylinder, cylinder head and cover & cowling were pressure die-cast in high silicon aluminium alloy by an outside firm to our design.

The manufacture of this engine was tooled up in a responsible way.  For example: the cylinder & crankcase unit was mounted in a machine; all machining, boring, drilling, facing, etc being carried out completely automatically and simultaneously.  An unskilled operator loaded and unloaded the casting, going in as a casting and coming out ready for building into an engine in about 30 seconds.  This machine was designed and partially made by us.

Many thousands of these engines were made, in fact the normal daily output was just over 100 engines.  Although originally designed for a hedge cutter, it eventually got used in a motor scyth, lawn mower, motor cultivator and a power pack on a bicycle.  They were exported to most countries.  The engine, like the four-stroke, was built up to a standard rather than down to a price.

When treated properly, these engines have an excellent life, in fact I am constantly using a two-stroke made in 1955; the whole of the engine is original (not like the Irishman's shovel).  As production of the 2-stroke finished in about 1959, we no longer have any spares.

Teagle Minor Engine Data

Built under British Patents Nos 714619 and 730537 and Registered Design No 867520.

Single Cylinder 49cc Two Stroke.  Bore 40mm, Stroke 40mm

Normal Engine revolutions 3 to 4,000rpm.  Maximum revolutions 9,600.

Maximum Torque developed 22ozs at 1ft radius at 4,000rpm.


Cast from "41" Alloy for use at high temperatures.

Deflector type with two rings.

Ring Gap 0.55ins.

Connecting Rod

Drop Forged from RR56 Aluminium Alloy.

Small End Bronze Bush.

Big End Needle Roller Bearing.

Lubricated by oil mist conducted by scavenge through hole drilled in crankpin.


Internal parts by Petrol Oil Mist.  One gallon Petrol to ½ pint Oil = 16-1.

Outrigger Bearing.  Three shots light grease every two months.

Cylinder Liner

Centrifugally cast to Ait Ministry specification, 4K6.

Replaceable when excessive wear has taken place.


14mm.  3/8" reach.  Gap .022ins.

Lodge-CAN.  Plug Cover, Lodge R90.


Flywheel, clockwise rotation.

Ignition advance, 37° 28' = 7/32ins BTDC.

Approximate Petrol Consumption

¾ gallon per 8 hours.

First published - March 1984

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