Author Topic: Radial 3 outboard engine  (Read 2933 times)

Offline Brian.Garvey

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Radial 3 outboard engine
« on: August 06, 2014, 03:57:05 PM »
So....Ive been wanting to make one of these for about ten years.

I know this is a model engine forum, but given that the thing is going to be pretty tiny I think this is the place for it.

Before I start with the design, I want to run it by you guys of what you think of my 'plan'...

Everyone knows the problems with radials and the oil getting everywhere - Im cool with that so let me tell you how Im thinking of making it.

I would like to make it 4 stroke - I think this is fixed in my head so lets put the idea of two stroke out of our minds :Lol:

The block is basic enough - and will be a cast item.

I am pretty used of outboards, and all mine are watercooled - meaning you dont run them in the 'hinged up' position, so this may make oiling easier.
Ill probably use an old shaft/gearbox I have here - not fully decided on that yet but its likely. These also contain the waterpump so that would be another thing already made.

I dont like the idea of exposed pushrods or rockers, so Im swaying towards OHC like the honda lawnmower engines. These have the timing belt in the oil and driving out to the cam in the head.

Doing it this way would just mean making 3 heads the same and fitting three timing pulleys to the crank - all three stacked offset. I would think just offsetting the cam pulleys in the heads would keep the bores on all the same plane.

For cooling a jacket around bores would be enough I think? A copper ring could do as a gasket to aid in head conduction from the heads.

The jackets could be all linked with a hose/banjo fittings and exit back down into the shaft/leg through a stat - a small 3mm? hole ahead of stat would let air escape and keep the jackets primed and also keep hot water circulating out near stat. It also lets you know pump is still working :Director:

The crankcase would have a sump well around the crank bearing with the timing belts running in that well - the belts would transfer the oil out to the heads and back again, a paddle(or some form of splasher) would oil the rods/bores.

When the engine is hinged up, the oil would flow into a cast in tank between the lower two cylinders(I think/should)

The crank would have to extend out of the case on the top also for a pull start.

Around/under the pull start would be the intake chamber, isolated from crank case with tubes extending up to each head.
The exhausts would exit into a common ring.

A down draft carb would feed into this chamber, or a sidedraft mounted on a bend. Efi would be nice, but its too expensive, although I think perhaps a very simple efi system could be made since the load vs rpm is always in direct relation(fixed prop)
I think Ill just use a carb though, as you are into alternators, batteries, and fuel pumps then and thats a lot of messing.

For the heads Id probably use the complete honda camshaft and rockers and perhaps valves too just to save time. The heads on the honda ohc engines are part of the blocks so I would still have to cast heads. For the liners I would probably buy press in liners(dry) and MAYBE buy pistons from something else to fit said liners. Im not fully sure yet on the liners/pistons but I will definitely have to sleeve the bores dry to get around the dis-similiar metals in contact with the water(fresh water only but still....)

Conrod and master should be pretty easy.

Crankshaft, 3 piece I guess,

Bearings, maybe needles with hardened sleeves on the big ends, slip fit on the pin ends in pistons.

Crank case, ball race one side, cylindrical roller on the top for expansion issues.

Insert loads of other stuff I have overlooked or have not thought of here.......

What do you guys think?

Aiming for about 15hp at prop, which results in a bore stroke of about 60mm x 60mm....with a 2:1 speed reduction in leg gearbox.

Hmmmm.......

Brian,
« Last Edit: August 06, 2014, 04:49:46 PM by Brian.Garvey »
''Timing, perseverance and 10 years of trying will eventually make you look like an overnight success''

Offline gbritnell

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Re: Radial 3 outboard engine
« Reply #1 on: August 06, 2014, 05:18:55 PM »
What you're proposing sound very feasible but as with any 'new' design it really can't be proven on paper. That means building the prototype and then making any modifications once it's running and the gremlins pop out.
Sound 4 cycle practices, bore roundness, ring fit, valve sealing etc. are naturally required. Beyond that who knows.
Good luck with your project and keep us informed.
gbritnell
Talent unshared is talent wasted.

Offline Brian.Garvey

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Re: Radial 3 outboard engine
« Reply #2 on: August 07, 2014, 03:43:30 PM »
What you're proposing sound very feasible but as with any 'new' design it really can't be proven on paper. That means building the prototype and then making any modifications once it's running and the gremlins pop out.
Sound 4 cycle practices, bore roundness, ring fit, valve sealing etc. are naturally required. Beyond that who knows.
Good luck with your project and keep us informed.
gbritnell
How very true. I think Ill just layout the basics and proceed to jump in the deep end.

Brian,
''Timing, perseverance and 10 years of trying will eventually make you look like an overnight success''

 

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