Hello everyone,

I'm using this 34cc engine from a power sprayer (only one available here; never seen a Ryobi/Homelite etc. in the flesh) to power a 10' wingspan plane that a friend is building. The real-life purpose of the engine is to turn a 12" blower from which fertilizer is sprayed.


http://img125.imageshack.us/img125/9772/greaves2oy.jpg



Its a 34cc putting out about 1 hp @ 5500 rpm in stock form.

I have ported the engine and made a tuned pipe for it. Right now I'm using a 16 mm Zama carb from a Stihl Chainsaw. The stock one is a float type and is also too small at just 10mm.



http://img447.imageshack.us/img447/277/dsc000618by.jpg

http://img347.imageshack.us/img347/2964/dsc000661ap.jpg



The engine used to do about 4500 rpm with the blower as a load. After mods its doing about 7000-7500 rpm so I reckon it must be putting out more than twice the original power.

The problem we are facing is one of weight. The stock engine weighs about 3.5 kg with pipe, manifold and carb.

http://img179.imageshack.us/img179/3...c00004a5xv.jpg

I need help on how to reduce the weight.

My ideas on what could be done: -

1) Reduce 1/3 to 1/2 the web thickness on each side of crankshaft. This will bring weight to ~430g. (what effect will this have? other than a possible failure)

2) Remove unwanted material on cr. case L & R. Good for 100g decrease.

3) Make new intake and pipe from aluminum. Good for 350g decrease.

3) Do away with magneto completely somehow. (Need help on how to do this).

If I get the engine down to about 1.5 kg I think it should be enough.

Guys please give me suggestions on how to put this engine on a diet.

Unfortunately that engine has a cast iron cylinder,...I doubt you will get it down to 1.5kg

edit sorry was looking at first picture, the other pictures appear to be a different engine, i have no idea

The engine in the first pic has a different cyl block and head. The one I have has an integral block and head cast from aluminum. There is a 2 mm CI liner pressed into the block.

Welcome to the club! The engine you have looks like an excellent one for it's purpose. The mods you have made prove it has good potential. Unfortunately, it appears to be too well built to have good flying potential. It would be better to start with a chain saw engine. If you are determined to use this engine, cut off everything that doesn't look like an airplane engine. Do NOT lighten the crankshaft as this would make the engine out of balance and cause severe vibration. The magneto can be eliminated by using battery CDI, (check CH Ignitions website). Lots of luck and keep us posted on your results.

I too have an engine off of a blower with cast material on sides of fins for air direction. Plan on cutting it off to improve airflow and reduce weight.

On some engines I have cut the fins off a little making the top of head have round shape.

Could not tell for sure just how you mount this engine? Looks like 4 bolts on bottom in one picture.

The existing carb adapter is heavy and a heat conductor which is not good. Consider making one from insulator like material (G10 or aluminum, even just laminate some good plywood to get the thickness you need (seal wood again after drilling holes, use to pieces of glass to press faces tight.

Post some additional pictures of back side and current mount system may help with ideas.

Hi,

Mike the engine is mounted to the airframe using three bolts (red arrows) which are parallel to the crankshaft axis. It also has four tapped mounting holes (blue arrows) on the bottom which we are using for a speedboat.



The pipe is what gives the engine so much punch....without it I cannot get away with using low compression and somewhat high timing. Planning to use aluminum for the final pipe on the airplane.

Cutting off half the crank and some of the cyl. blk. is a good idea as you said.

After reading some posts here I am thinking if it would be worthwhile to try out a glow (gas+methanol) conversion for this engine. What do you guys think?

Cut off the rear shaft from the crankshaft about 1/4" outside the seal or cut it off inside the seal and install a plug in place of the seal. Every gram you can remove from the engine is valuable because it has to be balanced by weight in the tail. A phenolic intake manifold will insulate the carburetor from the hot cylinder and save a lot of weight. Because of the heat loss, aluminum pipes are not as effective as steel pipes. You might want to get in touch with Dick Hanson because he is by far the most knowledgable about tuned pipes and the effect of materials. Possibly the most effective pipe would be a steel header and carbon fibre chamber.

Thanks for the inputs bryan.

I dont think carbon fiber is an option. Maybe an aluminum pipe with ceramic coating could be possible