Preventing Gipsy Major engine failures
The CAA says that it has ‘identified information’ that suggests the use of Avgas 100LL fuel in de Havilland Gipsy major engines could cause reliability problems, particularly with cylinder heads, valves and valve seats, especially where bronze cylinder heads have not been modified to incorporate stainless steel valve seats, and these could result in a reduction of component life.
‘UL91 is the most appropriate fuel to be used by your Gipsy Major engine. Avgas 100LL can be used, but this may affect the longevity of the components. Unleaded mogas should not be used due to it containing octane enhancers, notably ethanol, which can cause damage to your engine, particularly nonmetallic components including the carburettor floats, rubber pipework, seals etc.’
It adds that ‘whilst the CAA recognises that a rough running engine or engine failure can be caused by a multitude of factors, one remedial action is to ensure the most appropriate fuel is used where available and that the engine is regularly checked by a qualified engineer’ and recommends that all operators of aircraft powered by Gipsy Major engines (whether on National Certificate of Airworthiness or Permit to Fly) ensure that routine checks on the engines are carried out by a company/person experienced on this engine type.
‘To ensure the engines are in a good and serviceable condition you should also have your engine properly checked if the engine is found to be running rough, or low compression is noticed when turning the propeller by hand,’ it advises.
UL91 is the most appropriate fuel for Gipsy Majors says the CAA