Engine

Please donate to the cause if you can, all funds will go towards the ongoing GX200 Eggmotor project. Thank you.

Power Plant

The first thing I wanted was the engine. I was going to purchase what I thought was the biggest in the range, a 13hp GX390 engine. By chance, I found out that a few ‘clones’ were made with larger displacements and more horse power without any additional cost in weight. The engine I purchased is known as the GX420 and thanks to a slightly bigger bore and stroke develops 15hp at 3600rpm.  There is another variant larger still, 439cc with around 17hp.

 

GX420 Engine

GX420 Engine

I am working to a similar specification in terms of power and propeller size to the tried and tested 2 stroke Konig/CRE SC-430 engine. With a 107cm prop and 20hp at 4200rpm it can develop <65kg thrust. The GX420 has a considerable weight disadvantage but should be much more fuel efficient and potentially just as reliable.

Konig/CRE SC-430 powered paramotor

Konig/CRE SC-430 powered paramotor

Tuning

In order to squeeze the necessary extra 5hp out of the GX420 I contacted my friend Shane at AGK .

As the engine won’t be spinning much above it’s designed range then a modified camshaft will be of little use. Shane suggested increasing compression by milling 0.1″ (2.54mm) off the cylinder head, improve the breathing and swap the heavy flywheel for a lightweight billet aluminium one.

Billet Aluminium flywheel has been purchased and fitted.

 

GX390 Billet aluminium flywheel

GX390 Billet aluminium flywheel

The cylinder head has been milled and a karting brake carrier hub modified to fit the Konig specification propeller.

 

25mm bore kart brake carrier hub

25mm bore kart brake carrier hub

For the improved breathing I’ve purchased an air filter and adapter kit from AGK. For the exhaust I brought a KTM type silencer off ebay and I also have some flexible 25mm exhaust pipe which fits snuggly into the silencer and I’ve bent the pipe to form a decent exhaust system. Additional items include a new head gasket, genuine Honda pulse fuel pump (not shown) and an 8.5litre fuel tank.

 

GX390 air filter and adaptor

GX390 air filter and adaptor

 

Exhaust can and bits

Exhaust can and bits

I’ve removed the engine’s governor to allow higher rpm and also the balance shaft too. There are mixed comments on the removal of the balance shaft in the karting forums but it saves a little weight and won’t sap power. So far the vibration is acceptable.

I estimate that the increased compression will give approximately an extra 2hp, improved breathing (+ carburettor re-jetted) an extra 1hp and the loss of  the heavy flywheel and balance shaft yield a further 1-2hp @ 4000-4200rpm.

My calculations estimate 57-59kg thrust, although I’d be happy with anything over 55kg.  On the down side though, with a full tank of fuel the complete EggMonster weight will be above 40kg.

The throttle arrangement will be the same as the original GX200 powered Eggmotor.

There’s a modified carb insulator with a pipe fitting so that I have a ‘feed’ for the pulse fuel pump. I could have taken a ‘feed’ from somewhere on the crankcase but there would be a risk of oil being sucked into the pipe.

 

Pulse feed modification

Pulse feed modification

Engine almost complete

Engine almost complete

Engine almost complete

Engine almost complete

As for the propeller, Born Propellors do a 108cm Konig prop for 149.50 euros. I have given into temptation and purchased one as they had an offer running through their ebay shop at 127 euros.

Engine almost complete, prop test fit

Engine almost complete, prop test fit

The following picture is now the completed paramotor (minus harness fitment and powder-coating). It will be trial tested with the 3 blade fan assembly although we are having issues with starting it due to the mass of the hub and 3 blades.

Complete with netting and 3 blade fan.

Complete with netting and 3 blade fan.

Completed Eggmonster

Completed Eggmonster

Completed Eggmonster

Completed Eggmonster

Completed Eggmonster

Completed Eggmonster

Completed Eggmonster

Completed Eggmonster

 

 

Advertisements
%d bloggers like this: