Gnome Rotary Engine Re-manufacture

HISTORY REMADE

On Friday the 31st January 2014 at 3.35pm history was remade at the Omaka Airfield, Marlborough, New Zealand. A moment of great excitement and relief after some initial issues around timing were resolved – then the distinctive firing of one cylinder – a puff of smoke – a moment’s hesitation and then the dream of re-manufacturing classic aircraft engines became a very loud reality for Tony Wytenburg and his team at CAMS Aero Engines as the Gnome burst into life for the first time. “There was no keeping it secret as the newly manufactured 100 hp Gnome CAMS 001 filled the air with the unmistakable smell of burned castor oil and the unique sound of a rotary engine on full song.” says Tony.

The first Gnome engine is nearing completion. Each passing day gets us closer to “getting smoke out of it” for the first time. Then there’s 20 hours of testing, complete strip down and reassembly before Gnome CAMS001 is delivered to its proud owner. To paraphrase Winston Churchill’s famous words, “that’s the end of the beginning”. Straightaway we are into production of CAMS002 and the other orders that we are assured by a number of prospects we can expect to receive as soon as 001 is shipped.

The engine is now mounted up on its test rig and we are working on building and assembling the test equipment.

We had the engine and prop on display at the recent Omaka Aviation Heritage Centre Flying Day and drew considerable attention. “The engine really is a piece of art.” was one of the comments we received on the day says CAMS owner Tony Wytenburg. “One recent visitor to our workshop commented ‘so this is where you put the magic in the metal’. We thought that was really expressive as a lot of the work that we do is more than just engineering – it has an element of art the way we ensure that corners are carefully radiused, surfaces properly finished, parts fit together perfectly.”

You can see from the photo that we have test fitted the prop onto the engine and at 9 feet (3m) diameter dwarfs the Gnome. The prop has recently had its test flight mounted on a Le Rhone engine aboard a Sopwith Pup. The prop greatly improved the Pup’s performance over its own prop so we are confident that it is close to right for the more powerful Gnome engine.

Early in December 2013 we received the valves from a manufacturer in the UK. They have been manufactured from 21-4n stainless, induction hardened and have a stellite tip. Compared to the original valves these are manufactured in a vastly superior material and will last a very long time.

The tapered prop shaft that bolts onto the front of the engine was manufactured in HT steel.   We also manufactured a broach to finish machining the keyways/splines in the washer on the prop hub (See the “How we do it section).  We then machined the prop hub to suit

We have also taken delivery of the custom made prop for testing the engine. It is based on a Sopwith Pup prop and it represents a beautiful amalgam of craftsmanship and engineering. The engine’s speed is limited by the resistance provided by the prop so it is a critical part of the setup. The overall diameter and pitch has been increased compared to the Pup prop so that we can clip it if needed to adjust the maximum engine revs.

The assembly of the engine is in its latter stages where we are progressively adding components and checking the clearances on each. The front cam cover was test fitted, the position of the cam lobe to the cam housing is critical. Once we were happy that this was correct we next looked at machining the holes for the cam timing gears. We decided to make a cutaway front plate which would allow people to see how the cam timing worked. This is quite remarkable, especially when compared to modern day cam set ups. The cut away front plate also allowed us to check the position of the timing gear holes before we finished machining the front plate.

Late in December 2013 we have taken delivery of the forged aluminium pistons from the USA. There has been a lot of technology advances in the manufacture of pistons over the years and we thought it wise to use the services of a specialist piston manufacturer to make a suitable piston to replace the original cast iron piston.

A visit from Gavin Conroy and the semi assembled engine with its cutaway cam cover prompted an impromptu photo-shoot (above) and a short video clip of how the cam timing works.