Engines for Sale

Thursday, December 1, 2011

Elfin 1.5 cc BB MkII

Elfin 1.5 cc BB Mk II
Circa 1956
 Reed Valve Details

 The Elfin 1.5 and 1.8 Share the Same Crankcase

 The larger 2.5 cc Engine with New Larger Crankcase

 The Reed Valve Design was its Secret to Performance and was Widely Copied

 This Elfin 1.5 MK2 has Poor Compression
Soon to be Fitted with a New Piston

Design History:-
Designed and manufactured in England in the mid 1950's

Design Features:-
Over square combustion chamber;
twin ball bearing supported crankshaft;
rear induction with reed valve; and
heavy robust design;  

Engine Type: Diesel
Fuel: Ether/Petroleum/Oil
Cycle: 2T
Cylinders: 1
Displacement: 1,498 cm³
Bore: 12,78 mm
Stroke: 11,68 mm
Other Information

Model Year 1956
Aerol Engineering Ltd., Liverpool, England
Aerol Engineering Ltd., Liverpool, England

The Elfin had a very good name in the past because of the very well running plain bearing engines. They had a high power to weight ratio and super fittings and finish. 
In 1957 they introduced the 1.5 cc BB engine, with its unusual shape and rear induction reed valve, like the earlier plain bearing engines it was also well built. 
The only limiting factor was the reed, or clack valve like the British call it. An engine running at 13000 rpm means the membrane must move 26000 times 1 (open and close cycle per revolution of the engine). The reed valve was possibly a copy of the cox reed valve, but It was also a source of trouble.
If the membrane becomes dirty of develops a small crack, the engine will not run correctly.
Later the Jena, Taifun, Frog and E.D. solve the reed valve problems by adding a fine mesh to prevent dirt ingestion.
Making the reeds from better materials also meant that they would last longer.
With those improvements embodied the reed valve design adds up to an outstanding engine.

Watch my short clip on the Elfin 1.5 MK II BB engine running with low compression.


This posting is prepared in collaboration with YouTube Channel valic000 Visual material and observations are by valic000

1 comment:

  1. Compression certainly looks low and for a used engine the exhaust residue should be clear not black. Black can be carbon from incompletely burnt fuel but most likely is something wearing badly. Suggest strip engine and check for cause of black exhaust residue. Could be bent and/or twisted conrod, bent crankshaft or machining error in manufacture of these components as well as errors in the piston, cylinder and gudgeon pin. Engine should hold compression forever, hot yet be free enough when turned slowly over TDC with a finger the following blade whips around to rap the back of the finger. This is the standard I achieve with rebores of diesel model aero engines.